Good question. I have been talking about heat a lot lately and many of my clients want a solution that will be 'off the grid' when the power goes out. There are a few ways to do this.
First let's look at your space. It is pretty small - about 340 sf. But it has a lot of windows facing north and a cathedral ceiling, both of which make the space less energy efficient. But you are right, I know Cape Cod and the winters are relatively mild.
Insulation before heating
You probably understand that the first thing we tell everyone is spend money on making the envelope of the house really well insulated, before you address the heating. Great insulation makes your heating load really small.
- If you are building and still have time then by all means put in really great insulation.
- Alternatively, maybe your space is already finished and you just need to add a heater.
Gas furnaces vs gas fireplaces
As a basic answer, gas furnaces work more efficiently (about 92% efficient) than a direct vent gas fireplace (about 85% efficient). A normal gas fire place insert that vents vertically through a chimney is not efficient and not a good option.
But most traditional gas heating solutions are too big for this space, as are most normal direct vent fireplaces and wood stoves - which will easily heat 1500 to 2500 square feet.
- You could quickly over heat your space using one of these. So we have to go small and get a bit more specialized.
- Depending on your insulation, you probably want something that only produces about 8,000 -12,000 BTUs.
And of course the one thing we want to remember is that it needs to work when there is no power. Ideally you want something without an electric fan. Direct vent fireplaces will still create heat without a fan, just not as well.
Ideally you also want something that vents. There are a number of vent-less gas heaters on the market today but I have read many cautionary tales about them and the general consensus is that they are not good for your health if not used properly can be dangerous.
Your specs and some products that meet them
You are looking for these considerations:
- 8,000 -12,000 BTUs
- no electric fan
Gas heaters with these specifications will vary in efficiency and should simply be checked for each one. For the most part, the wall heaters will be more efficient than the fireplaces. But the fireplaces will have aesthetic advantages and the actual cost difference of heating such a small space with such generally high efficiency options may be negligible.
Below are some good options.
Gas Wall Heaters and Fireplaces
- HomComfort room heaters are direct-vent units that have a modulating gas valve, a thermostat and long-life enameled heat exchangers. The fact that they require NO ELECTRICITY is a major plus. They come in 7500 BTUs which will heat about 300 sf and 12000 BTUs which will heat about 1200 sf.
- Newport Propane Heater/ Fireplace P-12000 by Dickinson Marineis a direct vent gas stove made for boats but has been used in many 'tiny houses.' A built-in blower provides good heat circulation. This does have a 12v fan. You may have to get two. I would talk to the manufacturer and tell them that you are in a house - not a boat. Your insulation is probably better than a boat.
- Woodstock Soapstone Company. This company is just up the way from you in New Hampshire. They have a tiny 17" x 15" gas stove called the Mini Franklin or the Cottage Mini Soapstone Gas Stove. Its 8,000 BTU heat output will heat a single room 100-400 sf. It comes with adjustable output and remote control.
If you are open to using wood
- The Kimberly Stove.A cool looking and extremely efficient option. It is made of stainless steel. It does cost about $2-3,000.00, but it will save a lot of money in fuel and you will always be off the grid. Tests against propane recorded that it uses approximately 40% less money to heat with wood in the Kimberly than to heat with a propane furnace. The stove has amazingly low particulate. At 3.2 grams per hour it is less than the EPA allowance of 4.1 grams per hour. And it will go 8 hours without re-fueling so you can get a good night sleep. If your house is well insulated, it will takes hours for the heat to dissipate and you can let the stove go for even longer.
Best of luck!