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A Superinsulated House in Rural Minnesota

A tight building envelope and plenty of insulation mean low energy bills — even for a home with electric resistance heat

Posted on Mar 16 2012 by Martin Holladay

Electric resistance heating systems have a bad reputation. While the required equipment is cheap (and sometimes cheap-looking), homes with electric heat are known for their high fuel bills.

Yet some residential designers are beginning to rethink the old prejudice against electric resistance heating systems. After all, if a house has a very tight, very well insulated envelope, the heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. can be quite low, and so can the utility bills — even when using an expensive fuel like electricity. Moreover, all-electric homes don’t need a chimney, avoid minimum utility charges for natural gas, and don’t have any worries about fuel storage, fuel fumes, or backdraftingIndoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney.. Electric resistance heaters have much fewer maintenance issues than appliances that burn gas or oil.

Finally, if the homeowners ever want to install solar panels on their roof, the electricity usage in an all-electric home can eventually be balanced by a photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array.

Integrated design works well

An excellent example of an energy-efficient all-electric house is one designed by Rachel Wagner (of Wagner Zaun Architecture) for Gail Olson and Erik Peterson in Esko, Minnesota. Gail Olson is the fourth generation of her family to live on the 65-acre farm where the new farmhouse was built. The home was completed in 2009.

Using an integrated design approach, Wagner pulled together a team that included the homeowners, builder Steve Johnson, and energy consultant Michael LeBeau (of Conservation Technologies). Wagner recalls, “I’m proud of how well the integrated design process went, from the site assessment, to interviewing the clients and understanding their needs, wants, and goals, to weaving it all together. It yielded a result that is pleasing and functional and really durable.”

The owners are delighted with their house. Olson said, “I feel incredibly lucky to have a designer and builder who work on low-energy houses in this climate.”


Location: Esko, Minn.

Size: 1,950 s.f. plus 1,200 s.f. basement

Basement walls: R-38 ICFs from TF Systems (concrete core with 4-in. EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. on each side)

Sub-slab insulation: 8 in. EPS (R-37)

Above-grade walls: Double 2x4 walls, 15 in. thick

Wall insulation: Dense-packed cellulose (R-54)

Attic insulation: 22 in. cellulose (R-80)

Windows: Duxton fiberglass-framed windows

Window glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.: Triple glazing; south fixed windows are U-0.17, SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. = 0.50; east, north, and west fixed windows are U-0.16, SHGC = 0.31

Siding: Fiber-cement

Roofing: Standing-seam steel

Design heat load: 15,100 Btu/h

Space heating: 6 kW electric-resistance boiler and wood stove

Heat distribution: In-floor hydronic tubing in basement slab; hydronic wall radiators elsewhere

Domestic hot water: 105-gallon Marathon electric-resistance water heater

Mechanical ventilation: Venmar HE-1.8 HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air.

Air leakage rate: 0.4 ach50

Cost: $436,210, including design cost and site work

Annual energy use: 12,858 kWh of electricity plus 1.5 cord of firewood

Homeowners: Gail Olson and Erik Peterson

Designer: Rachel Wagner, Wagner Zaun Architecture

Energy consultant: Michael LeBeau, Duluth, Minn.

Builder: Steve Johnson, Two Harbors, Minn.

The two-story, three-bedroom home follows classic passive solar design principles. Double-stud R-54 walls, R-80 attic insulation, and fiberglass-framed windows with orientation-specific triple glazing all ensure that space heating needs are extremely low.

It’s easy to frame double-stud walls

According to Johnson, the double-wall framing was straightforward. “The window rough openings were lined with boxes made from 1/2-inch OSB,” Johnson said. “The top plates were tied together by one layer of 3/4-inch plywood.”

Johnson is a fan of double-stud walls. “This was the first double-wall house that I had built,” he said. “I think one of the things that impressed me was how simple it was. What we need is ‘better building, less technology.’ It was really just a matter of building another wall inside of the outside one.”

The walls were insulated with dense-packed cellulose, and that part of the job went smoothly. “The insulation contractor had already insulated double-stud walls before, and they are very good at it,” said Johnson. “They knew how to pack it in there. The fire code requires that double-stud walls be divided into compartments with drywall or plywood, every ten feet of linear wall, so we sectioned off the walls, and that helped the insulation crew.”

Like many builders in Minnesota and Canada, Johnson uses interior polyethylene as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.. “We used Tu-Tuf, which is a high-quality poly, as the air barrier and the vapor barrier,” he said. “Adhesives and tapes stick really well to the Tu-Tuf. All the poly seams are lapped at a stud and taped with 3M tape. We used Tremco acoustical sealant between the bottom plate and the subfloor.”

Insulating the rim joists with cellulose

The integrated design process allowed Johnson to provide input on air sealing details. “The rim joist area was tricky, especially because we used floor trusses,” said Johnson. “This was an example of why it was nice to work with Rachel — she brought me in early in the design process, and I made some suggestions. We wanted to end up with a continuous air barrier and good R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. at the rim joists. We wanted the rim joists to have the same R-value as the walls. We designed a system on paper, and we told the truss company that we needed vertical members in the floor trusses in a strategic spot — the right distance away from the end of the trusses, under the plane of the inside wall of the double-stud wall above — so that we could install solid blocking between the trusses. That gave the insulators somewhere to fasten the fabric. After the cellulose insulation was installed, we added a layer of rigid foam as blocking. We caulked the rigid foam on all four sides, which was only possible because the blocking was there.”

Wagner enjoyed the challenge of coming up with a rim-joist detail that avoided the use of spray foam. “Except for the minimally expanding foam used at the windows and doors, it’s a house without spray foam,” said Wagner.

The blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. results — 0.4 ach50 — were gratifying to everyone on the team.

How should we heat the house?

Natural gas is unavailable at the site, and the homeowners and the design team spent some time considering a variety of heating systems. “My sense is that the air-source heat pumps aren’t efficient in our climate,” Olson told me. “Some people are installing ground-source heat pumps, but we felt that the payout was not worth the investment for us. Oil isn’t a very common option in this area. I didn’t want to have a propane tank in addition to electrical service.”

They eventually settled on using electric resistance heat. Instead of installing electric resistance baseboards, however, they went with an electric boiler. “One thing I’ve learned from Mike LeBeau is that a hydronic distribution system offers a lot of flexibility in the future,” said Wagner. “If the owners ever want to switch to propane or add a solar thermal system, they can. Those options wouldn’t be available if we went with electric baseboard units.”

Although many PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. designers warn against the installation of a wood stove in a tight house, Wagner didn’t hesitate to recommend one here — even though the air leakage rate is only 0.4 ach50. A Hearthstone Tribute wood stove was installed. “I have had no difficulties putting a wood stove in such a tight house,” said Wagner. “I’ve done it more than half a dozen times, all in houses testing at less than 1 ach50. In the houses that also have a range hood, we caution the homeowner to pay attention before turning on the fan. Two homeowners report having to sometimes crack a window when the wood stove is used at the same time as an exhaust appliance like the range hood or the clothes dryer. We’ve provided dedicated combustion air routes in a couple of the houses, but not all.”

The homeowners use their wood stove frequently during the winter. “We usually have a fire for 2 or 3 hours in the morning if it’s 10 degrees and sunny, say, or 20 degrees and cloudy,” said Olson. “We build another fire in the evening for 2 or 3 hours. We burn mainly aspen from the farm (we have a lot of aspen) along with some birch. If temperatures are below zero and cloudy, I usually keep a fire burning all day. I do need to crack a window in the basement if I am using our electric dryer and have a fire burning in the stove. Otherwise we get a backdraft from the stove. It’s convenient for me to do this because there is a basement window close to our dryer.”

Energy bills and construction costs

The local electric utility has a complicated rate schedule, but the bottom line is that Gail and Erik pay between 8.6 and 10.2 cents per kWh, including the monthly service fee.

On average, the owners are spending $1,227 per year on electricity, including the cost of space heat. They burn about 1 1/2 cord of firewood each year.

The construction cost of the Esko Farmhouse was $426,210. That figure includes design and construction administration fees ($27,300), the cost of an energy consultant ($1,500), and site costs ($31,410 for the well, septic system, and driveway). The cost for the Duxton triple-glazed windows was $22,000.

Lessons learned

When asked what she might have done differently, Wagner said, “I would have been a little more aggressive with the amount of south glazing. I adhered to the usual formula, making the south glazing equal to 8% to 9% of the floor area. But the house has an unusual layout, with the living room in the northwest corner. Because of that I think I could have pushed a little harder on the south-facing glazing, and increased it to maybe 10% or 11% of the floor area. The homeowners are using their heating system more than I expected. Their January heating bills are higher than I expected, and January and February are usually our sunniest winter months. So part of me is wondering, could the house be getting more southern gain? Have I been overworried about overheating?”

Wagner isn’t sure that the heating system was the best choice. “The electric boiler is not what I would usually prefer,” she said. “The owners are using more electricity and less wood than I anticipated. I thought they would use more wood, but the wood stove is just used for supplemental heat. If I had known that, I think I would have urged them to install a propane boiler.”

I also asked Gail Olson if she would have done anything differently. “I could have made the house smaller,” she said. “If we had wanted to make it more efficient, the foundation could have been a slab on grade instead of a basement. It would use less energy if it were smaller.”

A feeling of solidity, and no drafts

According to Steve Johnson, the project was a big success. “The homeowners deserve a lot of credit,” said Johnson. “They set out to build a really good energy-efficient home. They wanted to see how far they could take this. They went to a local design conference in Duluth, where they met Rachel — which was a good move. The design is not boring, but it has no bump-outs or cantilevers or beams that penetrate the envelope. The design was conducive to achieving these goals.”

Olson is very happy with her house. “I like the even heat,” she said. “It is spacious. We have views and a connection to the outside from almost everywhere in the house. The passive solar design is fabulous. The house heats up well in the winter and is shaded in the summertime. I love the deep window sills — I have two 6-foot tomato plants right now. I like the feeling of solidity that comes from these 15-inch thick walls. I grew up in a settler’s log cabin, and all my life I’ve always lived in drafty house. I love having reliable heat with no drafts.”

Last week’s blog: “Occupant Behavior Makes a Difference.”

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Image Credits:

  1. Mark Teskey
  2. Rachel Wagner

Mar 16, 2012 10:25 AM ET

Edited Mar 16, 2012 10:42 AM ET.

Super House!
by Doug McEvers

The performance numbers for this house are fabulous, about .75 Btu's per sf per Hdd. The dark and cold months of December, January and February make up the majority of the heating usage in a superinsulated home in a cold climate. For comparison puposes, new MN code built homes average about 3.5 Btu/sf/hdd.

The solar contribution is larger than one might think for a superinsulated home. I found it to decrease my Btu/sf/hdd from around 1.35 for a house with little or no south facing glass to .9 for a house with good solar orientation. High solar gain glass probably would have improved the best house performance.

Mar 16, 2012 10:58 AM ET

The electric heat portion of
by Dick Russell

The electric heat portion of the electric bill is indeed quite low, yet Wagner seems to express concern about use of electric heat being higher than anticipated. What the numbers don't show is what that part of the electric bill might have been without the woodstove. In a house like that, even a small woodstove will heat the house all by itself when in use (except for the basement).

Despite the owner saying: “My sense is that the air-source heat pumps aren’t efficient in our climate,” the COP of any air source heat pump always will be greater than 1. While the COP will fall off considerably as the outside temperature falls, the power use still will be leveraged substantially. It just seems to be a waste of power not to use it to drag some outside heat in with it.

I'm curious also about the apparent lack of an outside air kit (OAK) for the woodstove. True, a small woodstove draws perhaps just 40-50 cfm of air, that's still more than the natural leakage of a house that tight. While the draft through the chimney pipe will keep the stove drawing properly, the flow likely will put the HRV into imbalance to make up the difference, and that imbalance results in lower efficiency of the HRV.. I'd be interested in hearing why no OAK was used.

Mar 16, 2012 11:30 AM ET

Calculating BTU/sqft/HDD
by Dick Russell

I ran some numbers for the house, to see perhaps how Doug ran his. For area I used 3150 (1950+1200) sqft. For heating degree days I used 9818 ( For heat load, I used the table numbers (3777 kwh) plus the 1.5 cords of Aspen at 14.7 million BTU/cord 70% efficiency ( So my math goes:
(3777 * 3412 + 1.5 * 14.7E6 * 0.7)/(3150 * 9818) = 0.92 BTU/sqft/HDD, The woodstove is providing 54% of the total. Using the first year's electric heat use (3276 kwh), the total heat load comes to 0.86 BTU/sqft/HDD, with the woodstove providing 58% of the total (numbers assume same HDD and wood use).

Mar 16, 2012 1:07 PM ET

Response to Dick Russell
by Martin Holladay

Thanks for doing the math -- very useful calculations.

Mar 16, 2012 3:56 PM ET

Nice job, people.
by James Morgan

‘Better building, less technology’ - now there's a concept. Can't believe how small and simple that boiler is.

Mar 16, 2012 8:19 PM ET

by Doug McEvers


You read the information better than I did, I used 1/2 cord per year instead of 1 1/2. Hdd for Duluth, MN is 9,742 but that is 1970 to 2000 average, probably 300 or so less these days. A more accurate calculation would take the actual hdd for the period monitored, I guessed 8,500 average for the 2 years. My recalculation puts this house around 1 Btu/sf'/hdd using 70% wood burning efficiency. Aspen is a poor firewood and unless it is properly seasoned the Btu per cord could be a fair bit less than 14.7 million.

Mar 17, 2012 11:21 AM ET

hdd for Duluth
by Doug McEvers

Acoording to the Weather Underground the hdd for Duluth, MN for the period 5-3-09 to 5-4-10 is 8,715 and for 5-4-10 to 5-3-11 is 9,381. Average for the 2 monitored years is 9,048 hdd, average energy used for heating is 27,467,418 using Dick's wood heat calcs. My third and final attempt, .9737 Btu/sf/hdd.

This is a very efficient house, the .40 ACH50 is impressive. Would like to know about the mechanical ventilation rate and the HRV efficiency for further analysis. We sometimes overventilate very airtight homes and heating the ventilation air becomes a major portion of the heating load. Knowing Rachel and Mike, they did not scrimp on ventilation and I am all for being safe.

Mar 17, 2012 6:00 PM ET

Will the real HDD please stand up.
by Dick Russell

After posting, I googled for sources of HDD information. One site showed HDD for me (central NH) at over 14,000, high by a factor of almost 2! Even for Esko MN I saw a lot of variation. What's the "gold standard" for HDD data?

Mar 17, 2012 10:31 PM ET

Cloquet vs Duluth hdd
by Doug McEvers

If I put Esko, MN in the Weather Underground search, Cloquet comes up. Cloquet is probably closer to Esko and a more accurate hdd reference. For the period 5-3-09 to 5-4-10 the hdd is 9,215 and for 5-4-10 to 5-3-11 hdd is 9,435. This puts the Btu/sf/hdd for the house at .935

Duluth is right on Lake Superior, there is lake effect and also a bit of heat island in the city of Duluth I would think.

Mar 17, 2012 10:42 PM ET

NH 14,000 hdd
by Doug McEvers


The 14,000 hdd in NH is Mount Washington, 6,288 ft, a very cold place. Superinsulation would be a good choice there.

Mar 17, 2012 11:34 PM ET

Edited Mar 17, 2012 11:34 PM ET.

Nice write up. Thanks to
by j chesnut

Nice write up. Thanks to everyone involved for sharing some of the details and costs. Hadn't heard of Duxton windows. Also surprised how tight the house tested using poly as the air sealing layer.

Curious whether in theory an HRV (or a bypass in the system) could be rigged to provide additional combustion supply air while a wood stove is being fired.

And why such a big hot water tank? Future solar thermal planned or does it assist the electric boiler?

Mar 18, 2012 4:09 AM ET

Response to J Chesnut
by Martin Holladay

Q. "Why such a big hot water tank? Future solar thermal planned or does it assist the electric boiler?"

A. No, it doesn't assist the electric boiler. Your first guess was correct.

Mar 18, 2012 11:46 AM ET

Wood heat
by Doug McEvers

As I look again at the specifications for this house I believe the wood heat contribution has been overestimated. I have experience monitoring similar homes in a like climate and I see so many thermal improvements on the Esko house to the double wall homes I built. The foundation is very well insulated, the windows are far superior, the ACH 50 is about 1/3 of my test readings. The HRV is likely far more efficient with much better control than was available in the 1980's. The design is very clean with a favorable surface to volume ratio.

It would be interesting to forgo the wood heat for a monthly electrical billing period to see the actual heating load. This is just a fine looking house and a great achievement for all involved. I applaud the owners for using the wood resource to lower fossil fuel usage.

Mar 19, 2012 9:02 AM ET

On calculating percentages
by Martin Holladay

Whenever someone calculates that (for example) "the wood stove is providing 54% of the space heat," one needs to ask the question: what else is under consideration?

Are you including internal loads? If so, what is the percentage contribution of internal loads?

Are you including solar gain through the windows? If so, what is the percentage contribution of the solar gain?

Mar 19, 2012 8:36 PM ET

Base usage
by Doug McEvers

The summer electrical usage provides the data for the non-heating portion of the electrical bill. From this summer monthly usage an internal gain of sorts could be estimated. Internal gains are not what they used to be with cfl's and higher efficiency appliances, unfortunately this is often offset with a house full of electrical gadgets.

The Esko house is efficient, not quite PH, but very close.

Mar 21, 2012 6:25 PM ET

House contruction and elec. heat
by Paul J. Boniface

I'm in the process of designing an addtion to my summer home, whiich will become a permanent residence in the future.

I am alined with the thoughts about const. with the above house, but have a few ides that are different.

1) I would use insulated panels on the outside rather then using double wall const.
2) In place of the electric system, electric radiant floor heating would be my choice.
3) To me, make-up outside air for thr stove would be mandatory.
4) PV panels will be incorporated on the gargae roof.


Mar 21, 2012 8:01 PM ET

Why cellulose?
by Patrick Aubrey

After looking at the photos and reviewing the article it seems using a loose fill insulation proved a little tricky in some parts of the structure? What was the reasoning for going with a loose fill, like cellulose and not a polyurethane spray foam?

Mar 21, 2012 9:03 PM ET

Response to Patrick
by Martin Holladay

The list of reasons is long... But I'll start with cost, embodied energy, and environmental impact.

Mar 22, 2012 10:17 AM ET

Deceptive Headline
by Michael Anschel

The headline and opening discussion suggests, shockingly, that you are about to build a case for electrical resistance heating as a primary source option. I read the article thinking you had completely lost your marbles this time and was even more shocked to find out that this was one of Rachel's homes. That was when I knew something was up.

There is no one in the green building movement in MN who advocates for, or would ever advocate for, the use of electric resistance heating as a solution UNLESS it was off the grid and using an alternative electricity generation method. The region's primary electricity generation comes from coal and the mercury contamination of lakes/streams/fish in MN is absurdly high. Folks are advised not to eat more than a couple lake caught fish a month because the levels are so high. (But that is an environmental issue and not something you are fond of discussing)

It looks to me like Wagner was advocating for her wood burning stove (which I find absurd for a different set of reasons) as the primary and her resistance boiler as a second. It would appear you also struggled with the burning of wood in a stove as an option here, but I see nothing in the design of the house, the architect's intent (misguided or otherwise), or the results that suggests for a one second that Electrical Resistance Heating is an option that should be considered.

In fact, Martin, it would appear that this home makes a case for propane.


Mar 22, 2012 10:33 AM ET

Response to Michael Anschel
by Martin Holladay

In the article on this page, I think I accurately reported the decision process that led the homeowners and architect to choose electric resistance heat for this house. This case study reports on a project; it is not an advocacy piece.

Obviously, homeowners, builders, and architects make decisions like this all the time, and any reader is free to come to a different conclusion. I'm reporting on one story, and on the decision of one particular design team.

As I pointed out, one of the advantages of an all-electric house is the opportunity to balance the home's electrical use with a photovoltaic array. Many people all over the country are choosing to do this; as I reported in the article above, Gail Olson and Erik Peterson have not yet purchased a PV array, but they could.

Anyone who feels strongly that propane is a more appropriate fuel than electricity should call up their local propane dealer and ignore the example of the house described here.

Sep 24, 2012 3:48 PM ET

Response to Dick Russell about OAK for wood stove
by Rachel Wagner

Dick, Better late than never, I hope. We struggled with the question of whether or not to install a dedicated combustion air route for the wood stove. In the end, the builder, performance consultant, and I all agreed that the home would have enough combustion air for the wood stove (and it does). I don't think it is possible to put the HRV/mechanical ventilation system "into imbalance" because it the system is, by definition, a balanced ventilation system. The amount of air supplied and the amount of air returned remained pretty much equal in this closed system. Now, because it is so tight, the house can go under negative pressure when the dryer or kitchen exhaust fan runs, since each of those appliances exhausts about 150 cfm. And this is where the woodstove can be problematic, since the stove and chimney might be the easiest route for make-up air to be claimed. And so this is why we suggest our homeowners to crack a window in a super-tight house with a wood stove and another exhaust-only appliance. But, as I understand it, the combustion air intake for the wood stove would not have solved the problem of the wood stove-make-up air conflict in a tight house. Hope this helps.

Oct 4, 2012 12:39 PM ET

by Steve Hansen

After reading the blog about high-end windows being a waste of money, how do you think cheaper windows would affect the performance of this house, and how much $ would they save?

Oct 4, 2012 1:07 PM ET

Response to Steve Hansen
by Martin Holladay

Good question. To find the answer, the designer needs to use energy modeling software to model the house two ways (with two types of windows under consideration).

Then it's up to the clients to decide what they want -- and whether the annual energy savings of X dollars justify the additional investment of Y dollars.

My own opinion: in a cold climate, triple glazing is a good investment for comfort reasons alone.

I think that the real debate concerns whether expensive Passivhaus-certified windows from Germany can be justified; such windows cost much more than the Duxton windows from Canada used on this house.

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