Heating a super-insulated airtight house in a cold Northern climate

The biggest question mark for us up to this point was, “How the heck are we going to heat this place?”

First there are a couple of caveats:

  1. 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 neighbour ask us if we would consider bringing it in. But this just seemed ridiculous to me. For a cost of $20,000 you can pipe in a non-renewable resource, 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.
  2. We do have power to 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-based) or ‘natural’ gas will often select the apparent lesser of two evils and choose natural gas for heating/cooling and 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 up solar panels and generate not only our own electricity for heating, but also our own power for running everything else in the house.
  3. We are putting in a wood burning stove as a back-up 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 firewood and plant a tree in its place.

Ok, so now that we have the prerequisite information out of the way, there were still huge decisions to make. Over the past few months I’d read innumerable articles on heating options for northern climates and in particular, super-insulated houses, as well as received everyone else’s biases on the optimal heat source. I soon realized that there are dozens of different options and all of them have their own pros and cons.

Most Passive houses that I read about used a “Mini-split heat source”, the majority of which were made by a company called, “Fujitsu” out of South Korea. These are pretty cool little devices. The popular choice with most houses I read are the ductless mini-split. In a Passivhaus, the heat load is so low (usually between 10,000 to 15,000 BTUh – as an aside most standard furnaces are 60,000+ BTUh) that usually two of these little systems are sufficient for heating a 2000 sq.ft 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, preheats it and delivers it to the indoor unit for distribution. In the moderate climates of Asia, Europe and the US these are great. A major appeal for these is that in the summer they act in reverse providing air conditioning. However, in a northern climate, such as Saskatchewan, though these are likely not the best option. Previously these units would be able to preheat air as low as -5°Celsius (23°F). Fujitsu has recently come out with a new model for “Extreme Low Temp Heating”, which will heat up to -25°Celsius (-15°F) outdoor temperatures. Unfortunately, this is still 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°Celsius (-22°F) or colder. A couple years ago for the entire month of December it did not get above -25°Celsius (-13°F) for a high! There will be a few days, every year, when it is -50°Celsius (-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” mini-split to cope with that I’m afraid.

If we were to use the mini-split system then we would need to have back-up heat sources in each of the rooms of the house such as radiant wall panels or baseboard heaters to manage the cold whenever it dropped below -25°Celsius (-13°F). Although these radiant heaters are relatively cheap at less than $100 each, I must admit that I think they are kind of ugly. Well, uper 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 mini-splits 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 moulding, no baseboards. Adding BASEBOARD HEATERS just seemed like a mortal sin to our minimalist aesthetic.

Ok, breathe…

Another option that was brought forward was to use an electric reheat coil. Basically how this worked was like a typical forced air ducted system, but a little bit different. A no-brainer must-have 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, mold and air quality. We had already decided that we would use a Vanee HRV (this was developed by Dirk Vanee through the University of Saskatchewan who is credited with developing the first widely available and mass produced HRV systems) 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. How the reheat coil works is by being mounted in the mechanical room at the outlet to the fresh air thereby preheating the 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, but only because it is a super-insulated house, in a conventionally built house you would need separate ductwork. For this reason, this leads to the claim by some that in Passive Houses “conventional heating systems are rendered unnecessary throughout even the coldest of winters” (a fairly misleading statement) as it uses the pre-existing ventilation system.

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. Secondly, this is basically a forced air system. A 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. Thirdly, 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. Fourthly, we would likely still need to supplement the system… and we’re not going to talk about that again.

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 1.5” concrete slab topper on the main floor of the house for passive heating purposes as well as the required 4” 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 indeed very comfortable. 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 imbedded in the floors. No wall panels, no horrendous baseboard heaters.

Fourth, it can be zoned and controlled. Each room or area 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 master bedroom and living/dining room do not need as much floor heat because the thermal mass and solar gain will heat these areas passively, whereas the north rooms and hallways do not have solar gain and 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 super-insulated and well-built houses:

“Radiant Floor Heating: Why radiant-floor heating systems don’t make sense for new, energy-efficient houses”

“All About Radiant Floors”

“Heating a Tight, Well-insulated 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 – reduce the use of non-passive, mechanical systems. The heat load, as mentioned of 10,000-15,000 BTUh, does not require a big system like 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!

Another concern was how we would deliver this heated water through the floor. Most systems use solar thermal panels that have water pumped to the roof to be heated through copper piping, then brought down to a storage tank and boiler that heats the water to upwards of 100°Celsius. This is then pumped through the floor in a closed loop system. As we found out from our recent well water testing, we unfortunately needed to use either a whole house reverse osmosis (RO) system or have water brought in by truck and stored in a cistern. The ramifications of this being that RO water is highly corrosive to copper piping. Crap! So what were we to do?

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 US. Indeed radiant floor would be overkill for those climates, but they do not get down to extremely low temperatures like us.

It was decided the best means of 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 R2000 and extensive energy modelling experience, the mechanical contractor and my wife and I. We went through 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 of setting up this system and concerns of overheating were alleviated in this meeting. We would use our solar PV system to power a simple, small 2-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. Although the thought still seems intriguing, in another few years this may have been the best solution. Check out this article for more information). On the domestic hot water side, we selected a fairly straight-forward, 47-gallon Bradford White high efficient electric 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.

PS. This post was edited from its original version on Nov. 23/2015.

 

6 thoughts on “Heating a super-insulated airtight house in a cold Northern climate

    1. Hi – we have spent our first full year in the house this week. So far so good. W be only started turning the heat on again in the past month here and last winter it worked well. I’m still figuring out the kinks a bit in trying to make sure we have in floor heat set at a comfortable level but not too high that when it is a sunny day we feel like we need to open a window because we are too hot. I’ve been keeping the in floor heat thermostats set to about 70F which gives us a few degrees of comfort for it to warm up with the sunny days, say up to 74F. On days when it’s not sunny I’ll start a fire in the wood stove which I live to use. In fact this winter I’m wanting to use it a bit more frequently as I love the heat it gives off. If we were to do it all again, I think we’d use the same system.

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