The size of your garage is a critical factor in choosing the right heater. A heater that's too small won't effectively warm the entire space, while an oversized heater can lead to unnecessary energy consumption.
Generally, for most people it's better to slightly oversize a heater for a garage vs what you would put in a house. The key word is SLIGHTLY. 200k for you is GROSSLY oversized. I believe for you, a 45-50k will work fine but take awhile to bring it up to temp. I'd personally go 60-80k.
For a 1 car garage with 200 sq ft to 300 sq ft, the estimated heater size is 15,000 to 25,000 BTUs. For a 2 car garage with 500 sq ft to 700 sq ft, the estimated heater size is 30,000 to 45,000 BTUs. For a 3 car garage with 750 sq ft to 900 sq ft, the estimated heater size is 45,000 to 55,000 BTUs.
it is best to have the right size furnace as oversize will cause too many on-off cycles. too small causes extended periods of running and the possibility that it won't handle extreme cold.
Your home will be uncomfortable. When your furnace is too big, it will blast your home with too much conditioned air at one time. This can make your rooms feel too warm when your furnace is operating and lead to major temperature swings in your home.
For example, in zone 3 to 4, which typically requires 40-45 BTU per square feet, you can determine that a 2,500 square foot home would need a 100,000 to 112,000 BTU furnace.
Your garage square footage determines the necessary heater size. You should aim for 20 to 30 BTUs (British Thermal Units) per square foot of space. You should go for more BTUs if you live in a colder climate.
Wide Coverage: Our 7500W high-power heaters can easily cover an area of 732 sq. ft. for heating.
To heat an average two car garage, you'll need a garage heater that is capable of heating roughly 6,000 - 9,000 cubic feet of air. We recommend getting a 30,000 - 50,000 BTU garage heater to get your two car garage to a comfortable temperature.
Best mini-split air conditioner size for a two-car garage
A small one-car garage requires a 6,000 or 9,000 BTU mini-split, but the higher the garage's dimensions, the larger unit is required. Two-car garages require a more powerful mini-split at 9,000 to 12,000 BTU.
The average sized 2 car garage's square footage usually ranges from 400 (20×20), 576(24×24), and 720 (24×30) square feet.
A 24,000 BTU system will generally heat and cool a space that is around 1,500 sq. ft.
Because maintaining a heated garage prevents damage to your home, it is a valuable asset to new homeowners. Heating your garage increases the value of your home for potential buyers in the future.
Larger heaters are more “efficient” and use less electricity. Larger heaters last longer.
To heat a 40×60 shop, which is 2400 square feet, you'll typically need between 108,000 and 132,000 BTUs.
A garage heater that is too large for the space will not heat the space more quickly. A heater that is too large for the room will continue to heat for an extended period of time beyond the temperature set point, wasting energy. We call this a temperature swing.
A good rule of thumb to calculate the size of the electric heater you'll need is 10 watts per square foot of space. For example, if your garage is 14' x 22', it has 308 square feet of floor space. You'd multiply that by 10, which would give you 3,080, which is approximately the wattage you'd need.
A rough estimate for a 3-car garage would be around 36 feet wide and 24-36 feet deep; however, it could be larger or smaller depending on the specific design and layout. When it comes to square footage, it should be around 864-1296 square feet.
In-Surface Radiant Heat
Unlike other heating methods, it heats a surface, rather than the air around it. In-surface radiant heat is one of the most efficient ways to heat a garage. Pros: Versatile option that can be installed in your garage floors, walls, or ceiling.
Heats up to 950 sq. ft.
When it comes to heating your garage, you do not need to heat it to a comfort level equal to the remainder of your home (often between 65°F – 68°F). Keeping your garage thermostat steady at a temperature between 40°F and 50°F will give you benefits to the three listed items above.
Calculating Your Garage Heater Size
Watts are easy enough to follow as they can be quantified by 10 watts per square foot of space. For example, in an area that is 20 feet by 24 feet you would need 4800 watts of power (it's just the total square footage, 480, multiplied by 10).
12,000 BTU – ~550 sq. ft to ~800 sq. ft.