I'm planning a 20×20' detached garage which will have a bonus room built into the roof trusses. I'd like to use this bonus room as my home office — so, since I live in the cold North, it'll need a heat source.
Given that the space will be thoroughly insulated, and that the only mechanical I can easily run from the house is electricity, how can I heat this space (12x20x7', just shy of 1700 cubic feet) in a reasonably efficient manner?
Considerations:
- As it'll be used mostly during normal business hours, the temp can be allowed to dip at night, but must stay reliably above, say, 50° (for the sake of the computer equipment)
- The faces of the gable roof are East and West (I'm open to insulated skylights and/or some kind of passive solar, if it'd help)
- If needed, I can run water lines to the space (the detached garage will only be about 12' away from the house)
- I'm open to some sort of burned fuel (pellet stove?), as long as the fuel itself is relatively inexpensive and widely available (I have access to as much chopped wood as I can burn, but something more compactly stored / consistently burned would be nice)
- The trusses will be customized anyway, so I can use a heavy / reinforced bottom web, should it be necessary to pour some kind of underlayment layer (for in-floor radiant heating or just plain heat retention via mass)
- The furnace for my home is fueled by our city's gas lines (may be possible to run a line to the office space, if needed)
Given all of this, what kind of heat source (or combination of sources) would get this home office through a cold Wisconsin winter in a reasonably efficient way (up-front cost can be higher, assuming the savings make up for it in less than, say, 5-7 years).
Edit: change text in last paragraph from "as efficiently as possible" to "in a reasonably efficient way", to clarify the scope of response I'm looking for.
Best Answer
Geothermal Heat Pump
Efficiency
If upfront cost is of no concern, a Geothermal heat pump is the most efficient heating/cooling system. According to the Department of Energy, geothermal heat pumps can be between 300 - 600% efficient.
Financing
There may be government programs available to help fiance the installation of the system, as well as state programs.
Payback
Some sources estimate a payback period as short as 3 years, though actual results may vary. If you switch your main house over as well, use the system for hot water, and take advantage of government programs. The payback period could actually be quite short.
Electric Baseboard Heaters
Efficiency
Since electric heat is 100% efficient, every ounce of electricity used it converted to heat.
Financing
If there is adequate space and power available in the service panel, an electric baseboard heating system is fairly inexpensive to install.
Payback
Depending on the cost of electricity in your area, electric heat may or may not save you money over other heating options.
Natural Gas Room Heater
Efficiency
Since it's a smaller area, a standalone natural gas forced air system may not make sense. However, a smaller natural gas room heater (or a few) might make sense. Natural gas room heaters can be between 65 - 100% efficient (depending on the heater), so they can be quite efficient.
Financing
As with electric room heaters, natural gas room heaters will be fairly cheap to install.
Payback
Again, depending on the cost of fuel. A natural gas room heater may or may not save you money over other heating options.
More Info:
The U.S. Energy Information Administration has a Heating Fuel Comparison Calculator (Xls) that might be useful.