We are on the hot chair indeed. Winter is closing in on us and we need the heating equipment installed. To get there we found ourselves exploring some hot and some not so hot options. Here is the story in installments.
Let’s start with the design workshop a little over a year ago. Even though we did not have the mechanical engineering expertise at the table we went home with many ideas on the shape and kind of heating system we need for the building.
We continued our research into the most appropriate systems during the following months and eventually were able to solicit the guidance and expertise of a mechanical engineer.
The starting point
Cathy and I are not fans of forced air systems. They sure are pretty cheap but the dry heat in winter and associated air flow feels very uncomfortable and we both get the creeps thinking about all the indoor air pollutants that get agitated, re-circulated and blown around.
I grew up with hot water radiators and I am a big fan because of their comfort and effectiveness. It did not take us long to add cast iron baseboard radiators powered by a solar hot water system to our wish list.
We would also like that same solar hot water system to cover the majority of our domestic hot water needs. For the cold and cloudy days, we dream of a biomass furnace as a backup to the solar hot water.
We quickly learned that the existing cast iron radiators are too powerful in terms of heat output for our efficient building envelope. I don’t have exact numbers, but based on a back of the envelope calculation one or two of our old radiators per floor would satisfy our heating needs once we are done insulating.
Our green team educated us about the 150 to 180 degree Fahrenheit needed to power cast iron baseboard radiators, on which we had our eyes set.
A solar hot water system operates at about 120 degree Fahrenheit, which would leave us with a delta of 30 to 60 degrees. To bridge that gap we would need a furnace. That would conflict with our zero-energy goal because of the frequency at which we would use the furnace.
Hydronic radiant floor heating would be a perfect match for a solar hot water system and the 100 to 120 degree water it could produce. Our problem is that there are existing beautiful hardwood floors throughout the building, which we would like to restore. Those stand in the way of radiant floor heating.
What about the systems that are installed underneath a floor, attaching to the subfloor between the floor joists? Well, we would have to push the heat through a subfloor, a small air gap and then the hardwood floor. Very old and very dry wood is not a good heat conductor, so we need a better idea.
No matter what we do, we will need a backup heat source to the solar hot water system. My dream of using a biomass furnace as a backup system quickly dissipated as the residential sized efficient models appear only available in Europe.
What about geothermal?
Geothermal would be a costly proposition. Plus, we would rather invest our money in an efficient building envelope, which would allow us to downsize the heating system and our energy consumption.
Similar to the cast iron radiators, the geothermal system would leave us with a temperature delta, in this case of up to 100 degrees Fahrenheit. We would end up paying a big electrical bill for the condensing pumps that would bridge that temperature gap.
Couldn’t we get the power from a photovoltaic array system? Yes, if it is big enough. But we would then be on the path of making everything bigger and more expensive, rather than smaller and more efficient.
Another option would be to dedicate a furnace/boiler to make up the temperature difference. But either option conflicts with our energy efficiency and carbon footprint reduction goals.