heating system

Walltherm wood stove & boiler

I found something interested on last weekends Edmonton Eco Solar tour: A wood fired fireplace / boiler.  Made by Wallnofer (from Germany, I believe) and distributed in Canada by Power Strength & Energy Solutions Ltd. (PSES, http://www.pses.ca), the boiler has two combustion chambers.  When a control arm of the side of the boiler is opened, an internal plate is lifted and the upper chamber of the boiler behaves like a normal fireplace.  This setting is used for 8 or 10 minutes after lighting the wood.  Once up to temperature, the side control arm is used to close the upper chimney port which forces the exhaust gases down to the lower combustion chamber where additional air is added causing the gases to burn a second time.  The gases then circulate up a chamber at the back of the boiler, past a water jacket that picks up some of the heat, and them up and out the chimney.  Interestingly, this design does NOT require the use of an electric fan to push to exhaust gases down.  (Obviously the pumps to circulate the water through the water jacket within the boiler require power.)  Note that in the pictures I took with my phone, a cover was removed from the side of the boiler to show the piping connections.  Under normal use, these would not be visible.

The results are impressive: an efficiency rating of 93%, 14.9kw/51,000BTU with 70% of the heat going into the water to be used for space heating or domestic hot water and 30% radiating into the room.  Given how much heat goes into the water, the representative I spoke to said that a storage tank of at least 600L was required and that 1000L of storage was better.

Here's a link to more information on the boiler: http://www.pses.ca/downloads/walltherm.pdf

The Riverdale Net Zero duplex (http://www.riverdalenetzero.ca) has a series of solar thermal collectors that store heat in a 16,000L water tank - practically the size of an in-ground swimming pool - built with concrete walls when the basement was poured.  I've understood from discussions with some of the people that worked on that project that there's a certain amount of heat loss just trying to store the heat from September into January and that the cost, complexity and performance means that design probably won't be used again.  When considering how we could store solar energy collected in the summer to use months later in the winter, it seems to me that nature provides us with the perfect solution: trees.  I find the Walltherm boiler to be a genuinely interesting design that allows us to use wood for more than just space heating.


Super energy-efficient homes: heat distribution

There have been a few questions about heating systems and heat distribution recently. I asked Canada’s green building grandfather if I could publish a paper that he wrote about how heat gets distributed in an advanced home. For your reading pleasure, written by Rob Dumont of Saskatchewan Conservation House fame:

Space Heat Distribution - Energy Answers by Rob Dumont

Wood Burning (part 2)


A Scan Andersen 10 woodstove, installed in the MCNZH.

People commenting on a recent national CBC article about Edmonton’s NetZero Energy houses spent a lot of effort criticizing the fact that the Mill Creek NetZero Home (MCNZH) has a wood burning stove. Besides proving beyond a doubt that the only thing worse than an ignoramus is an anonymous ignoramus, the comments taught me a bit about what messages to send in a sound bite culture such as ours.

For the record, the MCNZH will consume net zero annual energy without taking the wood burning stove into account. Even if we never burn a fire, the house will consume about 8000 kWh of electricity per year and its PV modules will produce about 8000 kWh per year.

Our Scan Andersen 10 wood stove has been installed, and we really love the quality of warmth that it radiates. Our source of wood will be construction waste from renovation projects in the neighbourhood. If we heated only with wood, here’s how big a pile the MCNZH would use annually:


A pile of tightly packed construction waste this size will heat the MCNZH for one year.

The pile is 1500 litres in volume, and it represents two thirds of a cord of wood (the cord would be 30% bigger because of the extra spaces between split firewood). We’ll be able to burn the wood very cleanly, because the stove is surrounded by the thermal mass of the concrete floors and a brick mass wall that will installed behind it. A quick clean hot fire will radiate heat into the mass, which will slowly release it into the house for hours afterwards.

Because the heat from the fire will be displacing electric heat from our baseboard heaters, we will in effect be converting construction waste into electricity. The wood stove should make the MCNZH a net electricity exporter of 2000-2500 kWh per year. Because the construction waste wood would have rotted in a landfill anyway, I consider it to be completely carbon neutral. That’s good for the environment, and wood heat provides a good deal of the resiliency that the times ahead will demand.

(cross posted at raisingspaces.com)

Solar Retrofit - Part 5: Unexpected Consequences

Here is a diagram from the IBC boiler installation manual showing the specifications for the venting.

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