Providing heating and air conditioning in your converted garage is an important piece of the project. You’ve got several options. Here’s an overview of the options and their pros and cons.
Using your Existing HVAC System
To do this, the system will have to be sized to accommodate the extra space. The good news is that most HVAC systems are oversized to begin with. Heating and cooling contractors play it safe by installing an AC that’s a half-ton to full ton too large and a furnace that has 20,000 BTU more than needed. Have an HVAC pro do a load calculation to determine if your existing system is sufficient. If it is, running duct work to the garage may be a challenge, but it can be done and may be your cheapest route to a comfortable conversion.
Installing a New HVAC System
You’ve got three choices here. If your home’s HVAC system is getting older, you could replace it with one that will accommodate the extra space. You can choose more efficient components than you currently have and probably keep your heating and air conditioning bills about the same – and maybe less – even though the system is serving more space. In warm climates, an AC or heat pump with a SEER rating of at least 16 is ideal. In cold climates, a furnace with 90% AFUE or higher is the right choice.
The second option here is to add a new split system to serve just the garage. A 1.5-ton condensing unit and a 45,000 BTU furnace might be sufficient. If your winters aren’t extremely cold, a heat pump is another great choice. You’ll need to locate the furnace or air handler in the garage attic or lose space by building a utility closet for it in the garage.
The third choice is to install a ductless mini split system. Most are AC-only, but some supply heating too. They are very efficient and quiet. You might want to choose a system that accommodates multiple indoor air handlers in order to serve separate rooms or create balanced temperatures in one large room.
Electric Heat and a Room AC
You can choose a space heater for the least expensive equipment or install baseboard electric heat which is quieter and more comfortable. The equipment costs for electric resistance heating will be less than for central HVAC equipment. The downside is that electric heat is expensive. You’ll have much higher heating bills. If you don’t plan to use the space as often as other parts of your home, heating it only when in use will cut your costs.
A window AC or through-the-wall AC is a good choice for cooling if you opt for space heating or electric baseboard heat. Some room air conditioners have a heating coil or use heat pump technology. The main problem is that room ACs are loud.
It’s not practical in every part of the country, but if you’ve got access to inexpensive firewood and local ordinances don’t permit it, a wood furnace can be very nice. Large outdoor models can heat water too. Indoor models are more affordable and prevent you from having to go outside as often. Wood pellet and corn stoves are good alternatives to a standard wood stove.
If you’re pouring a new floor, then hydronic heat is very nice. You’ve got to have a location for the boiler, and the costs can be prohibitive for many. For wood heat or hydronic heat, a room air conditioner or mini split AC are your best choices for cooling.
One way to cut heating and AC costs is to make sure the walls and attic of your conversion are well insulated. You pay for extra installation once, but you get lower utility bills every month forever.