Hi guys, Going to be building a single story 800 sq ft cottage that we would like to heat year round. Cottage will be on a slab, ICF frost wall and 8' ICF walls, with engineered parallel trusses to give a vaulted ceiling. Will insulate the trusses before finishing interior ceiling. In Ontario, Canada, winter can get down to -30C at times, usually -10C to -20C. Heat Loss study says 14,000 BTU. Would like to do in floor hydronic radiant heat, just not sure on the heat source. Is this small enough to get away with an electric hot water tank? Electric tankless hot water? Electric boiler? Propane also an option and in that case I would probably go with a Rinnai combi boiler which would handle the DHW as well. What's the best choice for install costs, reliability, and running costs? Propane is about 70 cents per litre here, and electricity averages about 20 cents/kwh with fees. Cottage will probably be used only a couple times a month in the winter (unless we start AirBnb-ing it), so another option would be to have a pellet stove as well, keep radiant heat set at 10C, then fire up pellet stove on arrival. I was thinking of this, as I assume the slab would take a long time to heat up from 10C to maybe 23C, so not ideal for a weekend use. Altho, I guess with internet and a wifi thermostat I could dial up the temperature remotely ahead of time? Thanks!

Electric might make sense as you have a pretty small heat load. Maybe exercise these calculators with your local fuel cost numbers:

https://www.borstengineeringconstruction.com/Heat_Loss_Analysis_Calculator.html

https://www.borstengineeringconstruction.com/Integrated_Heating_System_Performance_Calculator.html

If electric makes sense, you could save the cost of an expensive hydronic panel by using a NextGen Boiler:

https://www.borstengineeringconstruction.com/NextGen_Boiler.pdf

https://www.nextgenboiler.com/nextgen-14-4/

Full disclosure, NextGen Boiler is one of our affiliates. If you elect to use NextGen Boiler, please mention our referral as the small commission offsets the cost of maintaining these free DIY calculators. Please note that there are hydronic radiant floor heating design calculators on our website too. Thanks and good luck with your project!

Just be aware it my take many hours to bring the place up to temp. Like, up to 8 hours....

That's true, but at 800 sf feet one might not even want to setback the temp very much even when not there. We heat our 4000 total sf of home and shop buildings for under $30/mo using just an electric NextGen boiler. Of course it helps that we are in Southern Oregon with a balmy 23 degrees F outdoor design temp and largely renewable energy based and non-fascist controlled low 8 cents/kwh electric rate. Thank goodness I escaped Texas.

Insulate beneath the slab and insulate on the sides of the slab to keep the frost from creeping in. Embed a radiant heating system into the slab. If you use a self-regulating radiant heating system like STEP Warmfloor (https://www.greenwavedist.com/residential-floor-heating-systems) you can charge the slab with heat like a battery. We've used STEP Warmfloor in slab applications in Vermont/Maine and have been very successful.

Everyone on this forum puts down 1-1/2 inch of concrete over tied/stapled down tubing on the main level and then tie the tubing to wire mesh in thicker pads. All that specialty stuff is way to expensive and some even restricts heat flow....All tubing 1/2 inch with 12 inch spacing and max of 200 foot loops.