Editor’s note: Kent Earle and his wife, Darcie, write a blog called Blue Heron EcoHaus, which documents their journey “from urbanites to ruralites” and the construction of a superinsulated house on the Canadian prairies. GBA first posted a blog about their decision not to seek Passivhaus certification in May 2015.
The biggest question mark for us up to this point was, “how the heck are we going to heat this place?”
First, we should list a few conditions and limiting factors.
We had no natural gas to our site. This is probably a moot point anyway because even if we did have ‘natural’ gas we would not have used it. We did have a neighbor ask us if we would consider bringing it in. But this just seemed ridiculous. For a cost of $20,000 you can pipe in a non-renewable resource and then pay monthly fees for it for as long as it is available, and given the rising energy prices this cost is only going to go up and up.
We do have grid electricity at our site, but we intend to be net-zero or net-positive if possible. The power delivered to our site comes from the Queen Elizabeth power station which is a natural gas-burning. This is a big reason why people in places where you “must” choose from grid-tied power (which is often still coal) or ‘natural’ gas, select the apparent lesser of two evils and choose natural gas for heating/cooling and for appliances.
Still, there is a third option that people seem to forget: solar power! For less than or equal to the cost of bringing natural gas to our site, we can put solar panels on our roof with a battery and generate not only our own electricity for heating, but also our own power for running everything else in the house.
We are putting in a wood-burning stove as a backup heat source. Now, I know Passivhaus purists think that this is a bad idea and Wolfgang Fiest, the Passivhaus guru in Germany, has outright said that there are no wood-burning stoves that meet Passivhaus standard, but we don’t care. I know of nothing more comfortable than sitting next to a crackling fire. Also, wood is considered to be a renewable resource: cut down a tree for fire and plant a tree in its place. (I’ll write a separate post about wood-burning stoves later).
OK, so now that we have those issues out of the way, there were still huge decisions to make. Over the past few months I’ve read innumerable articles on heating options for northern climates in general and superinsulated houses in particular, as well as received everyone else’s biases on the optimal heat source. What I realized is that there are many different options and all of them have pros and cons.
The minisplit route
Most Passive Houses that I read about used a ductless minisplit heat pump, and the majority of these seem to be made by a Japanese company called Fujitsu. These are pretty cool little devices.
In a Passivhaus, the heat load is so low (usually between 10,000 to 15,000 BTU/hour — as an aside, most standard furnaces are 60,000+ BTU/h) that usually two of these little systems are sufficient for heating a 2,000-square-foot house with ease.
As the name implies, they do not use any ductwork, and essentially function like a space heater mounted on the wall. There is a pipe with refrigerant that passes through the exterior wall to an outdoor unit that draws air in, extracts heat from that air, and delivers a hot fluid (refrigerant) to the indoor unit. In the moderate climates of Asia, Europe, and the U.S., these are great. A major appeal is that in the summer these units act in reverse, providing air conditioning. In a northern climate like Saskatchewan, though, these are likely not the best option.
Previously these units would operate when the outdoor temperature was as low as -5°C (23°F). Fujitsu has recently come out with a new model for “extreme low temperature heating,” which will heat when the outdoor temperature is as low as -25°C (-15°F). Unfortunately, this is not sufficient for our cold Canadian prairie winters. Last year we had a record number of cold days for the winter: 58 days of -30°C (-22°F) or colder. A couple years ago for the entire month of December it did not get above -25°C (-13°F) for a high! There will be days, every year, when it is -50°C (-58°F) in the morning. That is insanely cold. If you have never experienced cold like that, it is really something to behold. Fujitsu would have to come out with a “Super-Duper Ridiculously Extreme Low Temp Heating” minisplit to cope with that, I’m afraid.
If we were to use the minisplit system then we would need to have backup heat sources in each of the rooms of the house, such as radiant wall panels or baseboard heaters. Although these are relatively cheap at less than $100 each, I must admit that I think they are ugly. Super ugly. Even the fancy ‘modern’ ones are ugly. I know, that shouldn’t be one of my criteria, but it is, I’m extremely particular and I think they’re ugly and cheap looking. And I think the minisplits are ugly too! Gah — the truth comes out.
You see, we like minimalism. Our house was going to be simply designed: no casing around doors and windows, no crown molding, no baseboards. Adding baseboard heaters just seemed like a mortal sin to my minimalist aesthetic.
Then there’s electric heat
Another option that was brought forward was to use an electric-resistance heating coil. Basically how this worked was like a typical forced air ducted system, but a little bit different. A no-brainer, must-have appliance for an airtight house is a ventilation system. If you don’t put one of these in then you are going to have serious problems from moisture build-up and air quality. We had already decided that we would use a Vanee HRV (this was developed by Dick Vanee through the University of Saskatchewan, who is credited with developing the first widely available and mass produced HRV system) in our place, which as with all other ERV/HRV systems, uses ductwork to each room or area of the house to deliver fresh air and draw out stale air.
Here’s how the heating coil works: It is mounted in the mechanical room in the supply air duct, thereby preheating the ventilation air before it is distributed to the house. The cool thing about this is that you can use the ductwork already present for the HRV system. This approach only works in a superinsulated house; in a conventionally built house you would need separate ductwork. For this reason, this approach leads to the claim by some that in Passive Houses, “conventional heating systems are rendered unnecessary throughout even the coldest of winters.” (This is a fairly misleading statement, as the suggested approach uses the pre-existing ventilation system to distribute space heat.)
There are a few downsides with this system, however. The longer the ductwork, the greater the heat loss prior to reaching its end point. We are a building a long narrow house and have one length of wall that is 48 feet.
Second, this is basically a forced-air system. An HRV flow rate is a lot less than a true forced-air system, but essentially you are just heating the air, not surfaces as is the case with “radiant” heat.
Third, this system cannot be well controlled. It is one system for the whole house. So in our living/dining room and master bedroom that get more solar gain, they would also get the same air heating, which could lead to overheating concerns.
Fourth, we would likely still need to supplement the system… and we’re not going to talk about that again.
The radiant floor option
A lot of conventional builders, and I’ll say “lay-people,” suggested in-floor heat. Actually they said if we didn’t use in-floor heat then we were idiots. OK, they didn’t quite call us that, but I felt their judgment. In-floor radiant heat is certainly appealing for a lot of reasons.
We planned to install a 1 1/2-inch concrete slab topper on the main floor of the house for passive heating purposes as well as the required 4-inch slab for the basement. And we also really like the aesthetic of nicely finished concrete floors (remember we are modern minimalists). But there was one problem: concrete floors are cold. When we told people that we might not use in-floor heat in the concrete, this is when their judging eyes showed themselves.
Second, in-floor heat is very comfortable without a doubt. We have several friends who have in-floor hydronic heat and walking into their house and feeling the warmth in the winter is very pleasing.
Third, you don’t actually see the heat system. It is embedded in the floors. No wall panels, no horrendous baseboard heaters.
Fourth, it can be zoned and controlled. Each room can have a thermostat installed individually with piping running specifically to each room with a sensor in the floor that allows for it to be controlled. This was a big bonus, because rooms like the mater bedroom and living/dining room do not need as much floor heat because the thermal mass and solar gain will heat these areas, whereas the north rooms and hallways do not have solar gain so would need to have a higher floor temperature.
OK, so you can begin to see where my bias was leaning. That is, until I started to read about radiant floor heating in superinsulated and well-built houses. (For links to some of these articles, see the “Related Articles” box above).
Too much heat for a not-so-crappy house?
Damn. The basic argument was that radiant in-floor is nice and makes sense in crappy houses. I don’t want a crappy house! Also the general agreement was that these systems were overkill. Passivhaus is called “passive” for a reason: the idea is to reduce the use of non-passive, mechanical systems. The heat load of 10,000 to15,000 BTU/h does not require a big system including a boiler, pump, and in-floor piping. In fact, when we talked to a couple friends who had built well-insulated houses with passive solar orientation, they told us that overheating in the winter did happen and they would have to open their windows in the dead of winter. This seemed crazy!
I had no straight answer and everything that I read either did not seem appropriate for our climate’s peak loads (coldest times of the year) or was apparently overkill. Sleepless nights were the result.
However, as I talked to others in the Passivhaus field, they admitted some problems with the Passivhaus model for a northern climate with frigid temperatures like ours. Passivhaus was really designed for moderate climates in Germany and a lot of the articles I had read were discussing moderate climates in the U.S.
Indeed, radiant floor heating would be overkill for those climates, but those climates do not get down to extremely low temperatures like ours.
Discuss options with the team
It was decided that the best means to make this difficult decision was to sit down as a team and discuss. We had a meeting with our team of four engineers, all trained in LEED building, one with Passivhaus certification and one with R-2000 (and extensive energy modelling) experience, along with the mechanical contractor and Darcie and I. We went through and made a list of advantages of each system — which essentially is what I wrote above.
In-floor hydronic heating was the clear winner.
All of my questions about setting up this system and my concerns about overheating were alleviated in this meeting. We would use our PV system to power a simple, small, two-element, 100% efficient electric boiler by Argo. (We did briefly play around with the idea of an air-source heat pump hot water heater from Germany for both in-floor heat and domestic hot water, but due to the high capital cost and potential issues of no one knowing how to service it here, we canceled this idea. The thought still seems intriguing, however, and in another few years this may become the best solution. Check out this article for more information.)
On the domestic hot water side, we selected a fairly straightforward, 47-gallon Bradford White high-efficiency electric-resistance hot water heater. We also planned to insulate this with its own extra insulated jacket. Really, in the end, it came down what is the simplest, most cost-effective solution to meet our needs.
As for overheating, the engineers would design the system so that areas hit with solar gain would not overlap with those of the in-floor system, while those not receiving solar gain could be controlled separately to deliver us the best of both worlds. On the extremely cold days, our little Norwegian wood-burning stove would take the edge off.
Boom. Decision made. Now I could sleep again.