Home energy system overview on the evening of December 31

Some noteworthy facts:

–We used 3,024 KBTUs of energy to heat domestic hot water (DHW); 2,402 of those, or about 80%, came from the solar heating system.

–We used 23,935 KBTUs of energy for home heating; of those, 1,554 (6.5%) came from the sun.

While those percentages are impressive, and in line with what had been predicted, it is also worth taking a momentary detour to examine the financial benefit of the $13,000 (retail) solar hot water system. The system produced 4,518 KBTUs of energy, which is about $45 worth of heat. Of that, the house used only about 3,950 KBTUs (~$39). Would I have saved more than $39 if I had taken the money and invested in more insulation? One thing worth noting is that we used almost 10x the energy to heat the home than we used for solar hot water. This is why perhaps I shouldn’t have oversized the system in an attempt to partially heat the home. Having a small system to heat the DHW makes sense, since hot water usage is fairly constant throughout the year. But oversizing the system in the hopes of providing partial space heating, as I did, might not make as much sense since you need another order of magnitude of energy, and the system produces the least just when you need the energy the most (ie on cold dark winter days).

On the plus side, the house only cost about $240 to heat so far this winter. Not bad!

–The underground air tube seems to be working great. At the moment I took the above snapshot, the outside temperature was -9F, and the tube pre-heated it to 27.7F. I should note that the next temperature meter, located just a foot or two further down the pipe, measured 36.2F, and I’m not sure I can completely justify why the temperature would have risen anther 8 degrees in such a short distance. Yes, that stretch of pipe is in the mechanical room, and therefore at room temperature, but 8 degrees in such a short distance seems odd. But the key is that the outside temperature is well below 0F but the fresh air is above freezing by the time it reaches the HRV. Despite the fact that we had a number of fairly extreme cold snaps, with extended periods of -20F, the HRV electric pre-heater has not had to turn on once.

–The HRV system is working great. The snapshot shows 100% efficiency, which can’t be completely right, but I’ve noticed it around 95% efficient at various times. My system is an Ultimate Air Energy Recovery Ventilator, and from this performance perspective I am very happy. However, the thing is noisy. There is quite a pronounced hum at low volumes, and when it runs at full tilt it sounds like there’s a truck idling outside. (It’s worse in my case because the laundry chute carries the noise from the basement right up to the master bedroom.) I had Mike McPherson come back and connect flexible hosing to the system, in the hopes that it would dampen the sound, but it didn’t help much. I also called the company but apparently they don’t really know what to do either. I could spend hundreds covering the box with sound-deadening material, but at some point I think I would just recommend a different system, even at the cost of a little efficiency. Since I am getting so much benefit from the underground air tube, perhaps we can sacrifice a little efficiency here in the name of quiet.

The system is now reset for the beginning of the year. Let’s see how the rest of the winter shapes up. In the meantime, a big shout-out to Jon Schafer of PowerHouse and Todd Hoitsma of Liquid Solar for installing and maintaining this great monitoring system!

To see the current status of the house, check it out here: http://www.welserver.com/WEL0250/

Our original plan had it on the staircase wall, like this:

original location of fireplace

and in elevation:

original fireplace location in elevation

It seemed so cool. We imagined a floating, wall-mounted sideboard that happened to have a fireplace in it, very modern and chic. We thought that we’d build a half wall over the staircase so that the stovepipe could run up it. In short, we spent so long planning it and discussing it that we were pretty blindered to reality by the time building happened.

As the wall was being built, we quickly realized that there simply wasn’t room for a big, horizontal, sideboard-type fireplace. I looked around and found a small stove that would fit. I took a photo of the wall and Photoshopped in the stove to scale:

The Rais stove photoshopped in to the staircase wall

We had lost our sideboard idea. We also realized that we liked the light coming down from the upstairs windows, and didn’t want to build the half-wall for the stovepipe. So the pipe would have to run in midair all the way to the upstairs ceiling. Less than ideal. But it still wasn’t enough to make us reconsider.

Our “the emperor has no clothes” moment happened when our friend Beth Cochran stopped by. “Why aren’t you putting the fireplace against that wall?” she asked, with all the guilelessness and innocence of someone who hadn’t spent months obsessing over the house in paper form.

We had our various rehearsed arguments we had thought of over the months when the entire project had been theoretical, but in the end we conceded she had a great point. We looked at it this way and that. I remember at one point thinking that both locations had their pros and cons, and that it probably didn’t make too big a difference in the end.

We played with little pieces of paper that represented the furniture on the living room blueprints to see how we might use the room differently. We realized that our main fear – that the room would become too narrow for the couches if the fireplace was against the wall – was essentially unfounded.

We moved the stove.

Here a few photos of what it looked like as it came to life:

The new fireplace framing

Once the stove was in:

The BIS Nova stove installed

fireplace with taped drywall

The move of the fireplace was interesting not for the facts of the case, but for the process of decision-making. I think it happens more often than you’d care to think: decisions that don’t get made as much as hardened as they accrete sufficient history, time, and effort. At some point there is just so much investment in the path taken that it is incredibly hard to look at the facts anew. Even when the facts are obviously in contradiction with the chosen course.

A few more notes regarding fireplaces that I learned while doing the research:

1. Traditional fireplaces are well-known to be a terrible idea from a heating perspective. When you light an open fireplace, you’re essentially creating a draft that pulls warm air up and out of the house. The fire radiates only a little heat into the room when it is lit, and at all other times the (typically metal, typically ill-fitting) damper allows heat to rise out of the chimney.

2. I was confused by the categories: wood stoves (applies to any wood-burning unit other than a traditional fireplace, but typically means a freestanding cast iron unit), fireplace inserts (designed to be inserted into an existing masonry fireplace), and zero-clearance fireplace insert (does not require an existing masonry fireplace, but still has fairly strict regulations regarding proximity to combustible materials.

3. Wood stove design has been completely overhauled since 1990 due to EPA regulations limiting the amount of smoke to 7.5 grams of smoke per hour. The best get down to about 1 gram/hour and can have efficiencies of 78%. They are typically free-standing pellet stoves. (See the whole EPA list as of Jan 10, 2010). Our zero-clearance insert is rated at at 4.8 gm/hr and 63% efficiency, ratings that are about standard for the style of stove.

4. Some of the higher-rated stoves have catalytic converters, which in theory are a great idea. Rising smoke travels through a honey-combed, catalyst-coated grid. The catalysts reignite the smoke, burning particulates and releasing heat. In practice, apparently, they tend to soot up quite quickly and require regular replacement. The other way of achieving reduced particulates and higher efficiency is to raise the temperature of the fire, which can be done through design and clever use of insulating materials.

5. We installed a hose for dedicated fresh air intake so our stove won’t backdraft.

6. Fans to blow air around the stove and into the room are a great idea. Make sure the model you choose has one.

7. There comes a point when you have to pull the plug on research. We were generally horrified by the curlicued, bad-bed-and-breakfast design of most wood stoves, and really liked the simple, clean lines of the BIS Nova. We also wanted a wood stove, not one built for pellets. And we’re not going to use this for primary heating; to a significant degree our stove will be for the ambiance.

The local brand of closed-cell polyurethane spray foam is Corbond. On their website they have a graph that looks like this:

More Insulation Is Clearly Useless. Or is it?

In an accompanying table of data, they state that the first inch of insulation reduces 72% of the heat loss. By the time you have four inches, adding a fifth inch reduces additional heat loss by only 1%. That inch of foam costs as much as the first inch (and insulates just as well), but is 72 times less effective. So was I an idiot for adding 12 inches of foam to my house? Maybe. Read on.

My initial thought was that everything about insulation is diminishing returns. Let’s say you built a house but didn’t put a roof on it. If you stretch a plastic sheet across the top, you’ll probably reduce heat loss by about 90%. If you replace the plastic sheet with a real wood roof, you’ll probably reduce heat loss by another 90% (for a total of 99% reduction). That means that ten dollars of plastic sheeting gives you 90% heat loss reduction. A ten thousand dollar roof gives you only a tenth of the additional heat loss reduction. So  why would anyone put on an actual roof–and then spend another several thousand dollars insulating it (to reduce heat loss to 99.9%, an additional reduction of only 0.9%)?

The problem with looking at insulation this way is what I call a frame of reference error. Did you ever see the Charles and Ray Eames movie “Powers of Ten” in science class in school? (If not, I highly recommend it: www.powersof10.com.) You zoom from intergalactic spaces down to the earth, spend only a few seconds in a ‘normal’ frame of reference – a park picnic in Chicago – and then dive into an atomic scale. The only reason the picnic appears to be the fulcrum between enormous and tiny is because that’s the frame of reference we understand. If we were atoms – or galaxies – then the tipping point between big and small would be shifted.

What does this have to do with insulation? Consider this: that Corbond graph showing insulation effectiveness would look exactly the same (aside from the numbers) if it went in 1/10 inch increments or in 10 inch increments. The first 1/10 of an inch is a lot more effective than subsequent fractions of an inch. The same holds when comparing increments of 10 inches.

So the only reason we think of those additional inches as being a waste of money is because we’re measuring on the scale of inches.

So how much insulation should we use?

The financially-minded title of this post, “diminishing insulation returns,” implies the answer. We need to look at the point where the incremental insulation costs more than the cost of the energy saved over the lifetime of the insulation. It really doesn’t matter whether the inch of insulation saves you 72% of your heat loss or 1% of your heat loss. It matters whether the absolute savings outweighs the absolute cost.

Here, of course, the calculation becomes fairly complex. Some largely unknowable considerations:

1. What’s the “lifetime” of the insulation? 30 years? 50 years? 100 years?

2. How will energy costs change over that time period?

3. What’s the net present value of those energy costs (ie what will the inflation rate be over the lifetime of the insulation)?

I would suggest that a conservative place to start would be to assume a 30-year lifetime, no change in inflation-adjusted energy prices, and ignoring the time value of money.

The guy who did the calculation of my house energy efficiency (Called a HERS rating – Google it), Matt Primki in Billings, provided me the following information: 1 square foot of R-1 insulation costs $1 to heat for a year in Bozeman (using $8/decatherm natural gas in a 8000 Heating Degree Day climate). Using that data and combining it with the cost and R-value of a specific insulation type, it’s easy to calculate the ideal amount of insulation. Using a 6.2 r-value/inch (typical closed-cell foam) at $0.65 per board foot (what my local guy charges; one board foot is a 12-inch square one inch thick), here is the calculation:

With these parameters, the 4th inch of insulation becomes partially uneconomic. Varying the parameters moves the “economically ideal” amount of insulation, although by less than I would have thought. Triple the price of energy, and you should use 6″ of insulation. Quintuple the price and you should use 7″. Triple the price of energy and assume a lifetime of 60 years, and the formula recommends 8″.

I was really surprised to see how little the recommended total insulation changed. I also learned that, from a strictly financial point of view, I potentially overinsulated my house in some places.

There is one important caveat if you’re using this approach to plan your insulation. As your house approaches Passive House standards (ie becomes so well insulated that a traditional heating system is no longer needed), the calculation changes dramatically. As you deduct the cost of the heating system, the cost of insulation effectively drops dramatically and the cost/benefit scale shifts.

Putting washing machines in the basement had a very practical reason: every once in a while, they leak. And when it’s on an upper floor, it can create an extraordinary mess. The environmental reason that we didn’t mind keeping the laundry away from the bedrooms is that we hang our laundry outside a good 90% of the time. So even if we’d put the laundry upstairs, we’d still be dragging the hamper full of wet clothes downstairs and outside. Or, given the convenience of everything on the upper floor, perhaps we’d use the dryer more.

Instead, Anne insisted we put in a laundry chute. It’s a fantastic solution to the dirty-clothes-in-the-bedroom problem and it eliminates half of the clothes lugging. Plus, it has the appeal of trap doors and hidden bedrooms: a laundry chute has such a wonderful retro feel that I approved of it on that basis alone.

Once we made sure to have the master bedroom straight above the basement laundry room, we discovered another bonus: the chute goes right by our first floor mudroom, so that when we come back from skiing and you want to unload your smelly socks, you can just dump them into the chute and off they go.

Another unexpected benefit was that the 2′ x 2′ opening that we left for the chute proved to be the perfect chase for our ERV ducts, our solar hot water piping, and the conduit for the wires we ran for our future photovoltaics – all the stuff that runs from the basement up to the attic. In the end, our laundry chute was about about 22′ wide by 18″ deep. Some photos:

the laundry chute opening in the upstairs master bathroom

the laundry chute in the mudroom

in the laundry room in the basement, the chute will empty into a hamper

I was researching Bozeman’s temperature data the other day to understand the weather conditions my house’s heat recovery ventilation system will face. On the Western Regional Climate Center’s website I found a table of data of daily highs and lows in Bozeman, averaged over the years 1971-2000. It was fascinating because the averages smoothed out into an almost perfect graph:

Daily Highs/Lows in Bozeman, MT 1971-2000

The graph almost doesn’t quite capture just how smoothly the average temperature rises and falls. For the first two weeks of January, for example, the average lows are 12.2, 12.4, 12.6, 12.8, 12.9, 12.9, 13.0, 13.1, 13.2, 13.3, 13.4, 13.6, 13.8, and 13.9. It continues that way, almost exactly 0.1 degree per day, until three days at the end of July, where the highs are 83.3 and the lows are 52.8, and then the temperature begins to slide back down.

I think of Bozeman weather as unpredictable. It can snow in July and it can be shirtsleeves weather in January. Yet when you average together just 30 years of data, weather has already given way to climate, and suddenly it becomes obvious: when it comes to a warming planet, even one degree has nowhere to hide.

See the complete data here: http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?mtboze

We have an in-floor radiant hydronic (ie water running through tubes) system divided into five zones. When I heard that the plumber was planning on five thermostats, one in each zone, that seemed like a lot of hardware on our walls. And then I got it into my mind that, c’mon, this is 2010, I should be able to control the temperature of my house from my cellphone, over the Internet, etc.

Aside from the gee-whiz nature of controlling the temperature from far away, I came up with two scenarios where it might be really useful: 1. You leave home on a trip and forgot to turn down the temperature (or just aren’t sure if you did). 2. The big downside of radiant systems is that they take a long time (several hours) to come to temperature. So I imagined us coming back from a long trip and pulling out our cellphones in the Minneapolis airport and turning on our heat so the house is toasty when we land in Bozeman.

Well. With the goal of having one central thermostat gathering input from five temperature sensors and then connecting the whole thing to the Internet, I quickly waded into a world of extraordinarily expensive systems. You can do absolutely anything, it turns out, but before you know it someone wants to charge you $5,000 for it.

The Internet-controlled BAYweb thermostat

So I started backpedaling. What if I still had five separate thermostats, but each was Internet-controlled? Here I had greater success. I found a great thermostat from BAYweb (check it out) that combines a really nice clean wall mounted unit with full Internet control.

But the Bayweb units are about $200 each. Your basic thermostat is in the $30-40 range. A 5-2 programmable one (ie you can have one programming setting for weekdays and one setting for weekends) are about $50-60. A 7-day programmable one (ie every day can have its own settings) are about $70-80. So the Internet control still adds quite a bit of cost, especially since we need five units.

In the end we decided to go with one of the BAYweb ones for the main floor, and then get 5-2 programmable thermostats for the other four zones.

Mechanical ventilation allows you to control the air flow in and out of the house. But the key to achieving the best of both worlds is a Heat Recovery Ventilator (HRV) or an Energy Recovery Ventilator (ERV).  They both extract the heat (or in the summer, the chill) from the stale air being exhausted and then pre-heat or pre-cool the incoming fresh air. With a transfer of heat efficiency in the 70-90% range, you can have consistently fresh air throughout the home without paying for it on your heating and cooling bills.

Read on to check out all factors involved in the decision:

The difference between an HRV and an ERV is that an HRV only extracts the heat from the air, while the ERV extracts moisture from the air flows as well. An ERV can be a good choice for two reasons: 1. If you live in a very humid climate, you want to keep moist air from entering the house. 2. There is latent heat in the airborne water. If you keep the humidity in the house from leaving, you can capture even more of the heat in your house.

our ERV: Pretty much the definition of "Black box techology"

We live in a very dry climate, so most websites will tell you that we should get an HRV. We ended up with the UltimateAir 200DX ERV because my research indicated that it was the most efficient unit out there. Even with limited moisture content, extracting the latent heat from the water is still important. I also decided that I wanted to protect the additional indoor humidity that we might have (eg from a humidifier, or cooking spaghetti – we live in such a dry climate that I didn’t want to lose all that).

Since we live in a cold climate, there was also one more important consideration. When the temperature outside drops below freezing, frost on the HRV/ERV unit becomes a big problem. You can easily imagine why – cold air is coming in, warm air is going out, and wham! Frost. There is no particularly graceful way of dealing with this. Most units simply run in a recirculation mode perhaps five minutes an hour when it gets below freezing. So the incoming air shuts off and the system just blows the warm indoor air around the heat exchanger. As it gets colder and colder, the unit spends more time in recirc mode. I think they get up a point where they spend 30 minutes an hour recirculating air.

That would seem to work fine, but at that point you’re spending valuable energy on simply running a fan. Even worse, I could imagine unfortunate bathroom smells being recirculated through the house.

Our Electric Preheater: Basically a glorified hair dryer

The other approach is to preheat the incoming air to a point where frost isn’t an issue. I liked that better, imagining that I could blow the incoming air over a heat exchanger coupled with my solar hot water. That proved to be easier said than done (it would require a separate water loop as well as a separate pump to move the water through it). The other option is to use an electric pre-heat. This sounds like a terrible idea–electrical heating!–but UltimateAir is fairly clever about it. The 200DX unit can handle air down to 10F without frosting up. So you only need preheating for several days a year, and avoid all of the wattage otherwise wasted on the recirculating cycles of other units.

Then there’s my in-ground air tube (read about it here). I don’t know how much it’s going to pre-heat my air, but if it manages to heat up the air by 5 degrees, then my electric preheat on my ERV only kicks on then it gets below 5F. I’m hopeful that will only be a few days, maybe one week, a year.

Designing the system

An important consideration is designing the duct placement. The broad idea is simple: You want to extract air from the “dirty” areas of the house (bathrooms, kitchen, laundry) and pump fresh air into the “clean” areas (bedrooms, living room). But one design goal I had was that I didn’t want to have separate bathroom fans in addition to my ERV. And to avoid that, you want to have the system powerful enough to clear out a bathroom after a big shower. The more air extract tubes you put in the house, the more that outgoing air flow is divided up between them. So we decided to put in only four extraction spots: the three bathrooms and the kitchen. I just put in a regular bath fan into the main-floor powder room, and I just skipped the laundry room.

ERV ducting through our attic

The 200DX can exchange 200 cubic feet per minute. If I have four extract points, that means 50 cubic feet per room. That’s not that wonderful jet-engine room-clearing power you can get out of a serious bathroom fan, but it seemed good enough to allow me to avoid extra bath fans. I wanted to avoid them for three reasons: 1. Bath fans cost money. 2. Installing the exhaust hose of the bath fan means yet another hole in the thermal envelope of my house. 3. All the air blown out through a bath fan contains valuable heat I want to capture.

I skipped the powder room because I figured that the room would get only occasional use. I put in the bath fan there so guests could “clean up” after themselves should the need arise.

HRV/ERV systems run most efficiently at low continuous flows. I expect to run our ventilation at about 70CFM. To clear out bathrooms, we’re also installing buttons in the bathrooms that you can push t0 boost the system into 200CFM mode for about 20 minutes.

Placing fresh air returns is much easier. Here the idea is simply to bring air to each bedroom and to each floor. The key is to avoid blowing air onto the inhabitants of the house. So hallways and behind doors is a much better place to bring in air than above the couch or a bed. It’s not very much air volume – at 70CFM that’s only just more than one cubic foot a second – so it’s more a dribble than the blowing we’ve become accustomed to with forced-air heating systems. Still, you don’t want that washing over you while you’re trying to sleep.

The ducts in the room are tiny because the system is very low-flow (compared to traditional forced-air heating systems)

Both fresh and stale air tubes run through our laundry chute to reach the upper floors

The stereo/data closet: smurf tubes in the back, blue data bundles on the right, green stereo wires

I have a confession: There’s a good chance I over-wired the house. But I succumbed to the now’s-the-time pressure of realizing that if I ever wanted to put in more wires for either sound, video, or data, then the easiest and cheapest moment is before the drywall goes up. It’s called “structured wiring” because all of the wiring runs back to a central location, as you can see in the photo on the left. (Each one of the wires that goes back to a central location is called a “home run.”)

Here’s what I wired in: data and tv wiring to ten locations and stereo wiring to six locations. Each data/tv wiring location has two RG6 (standard cable video wire) and two Cat5e (ie ethernet internet wire) wires. In addition, to each data/tv location I put in 3/4″ so-called Smurf tubes, which is flexible hose empty except for a pull string. The idea is that in ten years, when we’re all using fiber optics or whatever, you can then pull new wiring through the walls without opening anything up. Just tie the new wire to one end of the string and pull it through the hose.

Read on to see why I went this way.

Why 4 cables to every location? The short answer here is why not (the 4 cables come bundled and cost less than $1/foot). The slightly longer answer is that it provides flexibility for anything you’d like to do. For example, the only place I put in a traditional wired telephone is in the stereo closet. I plan on simply using cordless, Internet-based phones throughout the house. But if I do want to wire in a phone later, I can simply use one of the ethernet wires. Or let’s say I want to have one DVD player in the house feeding several television screens. I could then use the second RG6 to feed the signal back to the central closet and distribute it from there.

I spent a lot of time thinking about the stereo system. If you start looking online for “whole-house stereo systems” you can get quickly bogged down in the options. The big vision manufacturers try to sell you on is that your system should be able to simultaneously handle different music in every room and that everything is controlled by wireless controllers. (And also sell you silly visions of controlling all of your blinds etc via remote control.)

Probably the best value/money proposition in the whole-house music department is the Sonos (www.sonos.com) system. For people whose houses are already built, it’s also wireless.

There are also incredibly expensive whole-house systems that involve fancy in-wall touch-screen controls. They are both way too expensive and also not very future-proof: right now those touch screens seem really fancy, but I guarantee that in ten years they’ll seem horribly outdated.

I decided that building in so much flexibility and hardware was overkill. (And if I did go wireless then I would need to have a separate amplifier in each room, which is clutter I wanted to avoid.) So we chose to put in one central stereo with a six-speaker selector. In each speaker zone we’re installing an in-wall volume control. We hope that this will be a good combination of flexibility and cost efficiency.

I’m a little worried that our in-wall volume controls will seem outdated in ten years too. The other option would have been to go with a 6-speaker selector that is remote controllable. The Aton DLA-6, for example, would have allowed us to control the speaker selections and individual zone volumes from an RF remote. The reason we didn’t go with it is that I was afraid we’d always be losing the stupid remote. The in-wall volume controls might have certain limitations, but at least you always know where they are.

For music control you have to walk to the closet. But since most of our music will be coming off the laptop in the closet (MP3s, Pandora, Internet radio etc) we will be also able to control that from our mobile phones.

Of course, there are always those that say that the world will be wireless within 5 years, so why waste money on any of this stuff? It’s a good question. I ultimately decided to go wired for two reasons: 1) I think that wires will always offer higher speeds, greater security, and better reliability than wireless. 2) As long as you put in the wires as the house is being built, it just doesn’t cost that much. Of course, I’ll still put in a wireless router. Who knows? Maybe all of those data ports will primarily just collect dust.

Three last things I wired into the closet: 1. I put in a pair of wires from the master bedroom to the stereo closet so that we can watch movies in bed but run the sound through the in-ceiling speakers. 2. I also put in two ethernet cables from the mechanical room up to the closet, so that I can monitor electrical and energy consumption rates. 3. And I wired in USB cables so that we can connect two little webcams to keep an eye on the house (and our cats!) when we’re gone.

Here are the stereo closet design specs:

Stereo Closet Specs

Mike Mcpherson runs our blower door test

There are three ways that energy is transferred: radiation (that’s what makes your face feel warm when the sun is shining on it), thermal (that’s what burns your hand when you touch a hot stove), and convective (like when hot air rises). And here’s the thing about insulation: insulation is tested by how it slows down thermal transfer. When you’ve got a leaky house, then the stated insulation value written on the package when you bought it won’t mean a whole lot.

And all houses leak. Most of them leak a lot.

I don’t think there are any national standards when it comes to how airtight a house has to be built, but recently, a test called the Blower Door Test has become popular. We just did one on our house and learned some remarkable facts. Read on!

The idea behind a blower door test is to close all the windows and doors, putting a fan in the front door and depressurizing the house by blowing air out. Then an attached computer calculates the rate at which air seeps back in and presents it as the number of times all the air in the house would be replaced per hour. The Air Changes per Hour (ACH) is done at 50 Pascals of depressurization, so you’ll see the “ACH50″ number quoted when comparing houses.

Mike McPherson, the guy who did our house, compared the test to seeing how the house performs when a 20-mile-an-hour wind is blowing at the house from all sides. So the test does two things: one, you see how leaky your house is. And two, perhaps more importantly, you can walk around the house and feel where the air is blowing in.

Crappy houses might have an ACH50 of over 10. Well-built houses these days, Mike says, average around ACH50 of 5 to 8. Energy Star, the government program to highlight “energy-efficient” homes, require an ACH50 of 4 to 7 depending on the climate zone. Below 3.5 you need active air handling (ie the house is so tight that the air would get too stuffy without mechanically ventilating the house). Anything below 2.0 is really getting somewhere. The tightest standard I’ve come across is the Passive House standard, which requires a 0.6 ACH50.

When Mike turned on his machine, it said our house was 1.78, which Mike said was the equivalent of having roughly a 10×10 inch hole in my house open 24/7. The point of doing the test now, while the drywall isn’t up yet, is so you can walk around, plug the leaks, and make that hole smaller. And so we set out.

Check out this short video I made of the test:

As you can see, we spent the bulk of our time walking around behind Mike’s infrared camera and caulking all the holes he found. We went through three big tubes of caulk in an hour. The most common gaps were around the windows, although there were other things we found: nail holes, air gaps around ceiling can lights, and a few places where the foamers hadn’t filled wall cavities completely.

On a philosophical note, I was struck by how “smart” air was. The moment the fan was switched on air found every last single crack in the house and came streaming in. I imagined how complex a computer program you would need to model the entire house and the air flow so that you could find the tiny little nail hole a careless carpenter left in the upstairs middle bedroom. But the air molecules had no such worries. They just followed their nature and poured in.

So if the average house has an ACH50 of 5 to 7, how often does the air actually leak out per hour when the house isn’t pressurized? Dividing the ACH50 number by 20 is a good rule of thumb. That means that if your house has an ACH50 of 5, then all of the air in your house leaks out six times a day. And double that is quite common. If you have an ACH50 of 10, then all of the air leaks out every other hour! Talk about heating the great outdoors.

After plugging all the leaks, Mike turned on his machine again. 1.55. About 12% better, but I was disappointed, to be honest, that we didn’t make a bigger difference. Mike didn’t know what else to do. Usually, he said, it’s easy to make more progress, but sometimes all the work doesn’t do much. He claimed, plausibly, that our double-hung windows might be a culprit. Casement windows, since they clamp shut, are much tighter than double-hung windows, where the two windows just slide past each other.

We’ll do another blower-door test when the house is done. Mike thinks that we should get down to about 1.2 once all of the drywall, doorknobs, window trim, etc are installed. Let’s hope he’s right!

E.T. Foam Home

Using sprayed polyurethane foam for insulating is a no-brainer these days. It insulates much better than industry-standard fiberglass batts, both because it simply has higher insulating properties and also since the foam essentially eliminates convective heat loss (ie foam eliminates drafts). Closed-cell foams are also very rigid and contribute to the strength of the house.

Read anything on eco-friendly building, and you’ll find reference to closed-cell foam. It’s great stuff–at least in theory.

The local manufacturer of spray foam is Corbond. It has an R-value of about 6.2/inch. But I was a little suspicious that the guys who spray it in come dressed in hazmat suits. What’s up with that? Read on for some scary statistics.

All closed-cell spray foams are essentially foamy polyurethane, more or less the same stuff you use to protect wood furniture but with lots of bubbles in it. There are two mixtures that are mixed together as it is sprayed into place, the so-called A-side and B-side. The A-side is always isocyanate, and the B side is a proprietary blend of chemicals that includes the blowing agent.

The B side is mostly made of petrochemicals, which isn’t great from an environmental perspective, but I was really curious about the blowing agents. If you visit the websites of manufacturers like Corbond, they go to great lengths to highlight the fact that their blowing agents don’t deplete the ozone layer, but are curiously silent about the global warming potential (GWP) of the product.

I called Corbond and talked to a sales guy named Jeff. He sounded stumped by my questions about the blowing agent, ultimately saying that he thought no one really worried about the GWP of the blowing agent and that, in any case, the amount of energy you’ll save far outweighs any immediate climate damage the foam might have. That sounded valid. He also emphasized that about 90% of the blowing agent remains trapped in the hardened foam, so only about 10% offgasses. Again, a valid point, at least until the house burns down or is demolished.

When pushed, he said that the GWP of the gas is “probably about 4-6 times worse than carbon dioxide.”

Well, not really. I did some online research, and discovered that the blowing agent I was told Corbond uses, 245FA (trade name Honeywell Enovate 3000), has a GWP of about 950. 950! That means that about 2 pounds of the stuff is as environmentally damaging as a ton of carbon dioxide. And 245FA is the industry standard. Virtually everyone uses it.

It turns out that this is, in fact, progress. Spray foams used to use CFCs, and then HCFCs, the same stuff we used as refrigerants and that tore an enormous hole in the ozone layer. It was great stuff, from a technical perspective, but it was killing our atmosphere. We phased that out by the end of 2004 for residential foams. But while 245FA, which is now the industry standard, doesn’t kill the ozone layer, it is just as bad as the old stuff when it comes to GWP.

I searched around for foams that use other blowing agents. I found a company called Foam Supplies that make a blowing agent called Ecomate. Amazingly, it doesn’t damage the ozone layer, has zero GWP, no volatile organic compounds (VOCs), and apparently works great. I called the company and spoke with a guy named Scott. He told me that the company doesn’t sell the blowing agent for the home spray market, using it instead for the automotive, boating, and commercial construction insulation market. The owner of the company, David Keske, has no interest in selling to residential construction, he said. This is how Scott described David’s thoughts on the matter: “He said that when he’s dead his son can do whatever he wants to” with this family-owned business. But Scott doesn’t expect big changes anytime soon. He said something to the effect that David had been burned by non-payment by some home spray company about 20 years ago, and hasn’t forgotten the slight.

More research revealed a product called BioBased 1701s, a soy-based, water-blown closed-cell insulation. This sounded promising. It has an insulation value about 20% less than Corbond, but otherwise is a huge step in the right direction. (The “soy-based” thing is a bit misleading, as it still contains a lot of petroleum-based chemicals. But the main thing is that “water-blown” has no 245FA!)

Foam Installation

But what about this claim that you save so much CO2 because the insulation is so great? Well, that certainly has an important element of truth in it. Here’s my back-of-the-envelope calculation:

I will use about 1450 cubic feet of foam in my home. It weighs 2lbs/cubic foot. If 10% of that is the blowing agent, that means I’ll have 290 pounds of 245FA. At a CO2E factor of 950, that’s the equivalent of 125 metric tons of CO2.

To put that number in perspective: a round-trip flight from Bozeman to London releases 2 tons of CO2/passenger. The average American has a carbon footprint of 20 tons/year (A German, 9.5; global average 3.8).

Now I was starting to wonder about just how much this stuff contributed to the national carbon footprint. I put in a call to the Spray Polyurethane Foam Alliance and spoke with the executive director. In 2008, he said, the market for 245FA-spray foam was about 380 million pounds in the USA alone. If 10% of that is the blowing agent, that’s 38 million pounds. Multiply that by the GWP of 950 and you get 36 billion pounds, or 18 million metric tons, or about .25% of the entire nation’s carbon footprint. More than the entire country of Estonia.

When I asked the SPFA director why they don’t use water-based foam, he sounded confused. Hadn’t really heard about it. Companies make claims. Wasn’t sure. The bottom line: Honeywell wants to make money on its patent!

So what did I do? Here I have to make a confession. The 245FA-foam people gave me a quote of $11,000 for the entire house. The water-blown guy quoted me $17,000. I simply didn’t have the budget for an extra $6,000. I went with the bad stuff.