How To Size Your Furnace or AC

Q: What happens if my furnace or AC is the wrong size?

Oversized equipment short-cycles, which wastes energy, wears out parts faster, and leaves your home with uneven temperatures and poor humidity control. Undersized equipment runs constantly and still can't keep up on the coldest or hottest days.

Q: Do sizing tables replace a professional load calculation?

No. Sizing tables are a starting point, not a final answer. Your actual furnace or AC size depends on insulation, window count and orientation, ceiling height, duct design, and local climate, all of which a Manual J load calculation captures and a table can't.

Q: Do you offer free furnace and AC sizing consultations across the GTA?

Yes, Empower Home Comfort provides free in-home assessments across Toronto, Etobicoke, North York, Scarborough, Mississauga, Vaughan, Richmond Hill, Markham, Barrie, Hamilton, Oshawa, and Pickering.

How to size Your furnace/AC

Bigger isn’t always better!

Bigger isn’t always better,

its performance and efficiency that count. Before purchasing a replacement system you should always make sure your system is sized properly to match your needs and budget. Your Empower Comfort Consultant will thoroughly assess your home and comfort requirements to determine the proper size and make the appropriate recommendation. You can use the following tables to have a rough idea of What Size Fits Your House Better:

Furnace and Air Conditioner size for a Detached 2-story House

Detached House square footage *	Furnace Output [BTU/hr]		Air Conditioner size [ton]
Detached House square footage *	Built after year 1980	Built before year 1980	Built after year 1980	Built before year 1980
up to 1300 sq ft	40,000 BTU/hr	50,000 BTU/hr	1.5 ton	up to 2 ton
1300 to 1700 sq ft	45,000 BTU/hr	up to 55,000 BTU/hr	1.5 ton	2 ton
1700 to 2500 sq ft	55,000 BTU/hr	up to 65,000 BTU/hr	2 to 2.5 ton	2.5 ton
2500 to 3500 sq ft	up to 65,000 BTU/hr	up to 80,000 BTU/hr	2.5 to 3 ton	3 to 3.5 ton
3500 to 4500 sq ft	up to 80,000 BTU/hr	up to 100,000 BTU/hr	3.5 to 4 ton	4 to 5 ton
*The above square footages do not include the area of the basement

Furnace and Air Conditioner size for a Semi-Detached 2-storey House

Semi-detached House square footage *	Furnace Output [BTU/hr]		Air Conditioner size [ton]
Semi-detached House square footage *	Built after year 1980	Built before year 1980	Built after year 1980	Built before year 1980
up to 1500 sq ft	40,000 BTU/hr	50,000 BTU/hr	1.5 ton	up to 2 ton
1500 to 1800 sq ft	50,000 BTU/hr	55,000 BTU/hr	up to 2 ton	2 ton
1800 to 2200 sq ft	55,000 BTU/hr	60,000 BTU/hr	2 ton	up to 2.5 ton
2200 to 3000 sq ft	60,000 BTU/hr	70,000 BTU/hr	2.5 ton	2.5 to 3 ton
*The above square footages do not include the area of the basement.

Not sure which row fits your home? Skip the guesswork.

Get a free, no-obligation in-home sizing assessment from an Empower Home Comfort Consultant.

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or call 1-800-375-8984

Furnace and Air Conditioner size for a Bungalow

Bungalow Area [square feet] *	Furnace Output [BTU/hr]		Air Conditioner size [ton]
Bungalow Area [square feet] *	Built after year 1980	Built before year 1980	Built after year 1980	Built before year 1980
up to 1200 sq ft	40,000 BTU/hr	50,000 BTU/hr	1.5 ton	up to 2 ton
1200 to 1500 sq ft	50,000 BTU/hr	55,000 BTU/hr	2 ton	2 ton
1500 to 1800 sq ft	55,000 BTU/hr	60,000 BTU/hr	2 ton	up to 2.5 ton
1800 to 2500 sq ft	65,000 BTU/hr	70,000 BTU/hr	up to 2.5 ton	2.5 to 3 ton
2500 to 3500 sq ft	80,000 to 90,000 BTU/hr	90,000 to 100,000 BTU/hr	3 to 3.5 ton	3.5 to 4 ton
* The above square footages do not include the area of the basement.

Furnace & AC Sizing FAQs

How do I know what size furnace I need?

Start with your home’s square footage, age, insulation level, ceiling height, and window count — the tables above give a rough BTU/hour estimate based on those factors. For an exact number, a licensed technician performs a Manual J load calculation, which accounts for duct condition, air leakage, and local climate in ways a table can’t. That’s why every Empower Home Comfort quote starts with a free in-home assessment.

What size furnace do I need for a 2,000 sq ft house?

For a detached two-storey home built after 1980, that generally falls in the 55,000–65,000 BTU/hr range; homes built before 1980 usually need more due to older insulation. Bungalows and semi-detached homes size differently — check the table that matches your home type above.

How many BTUs per square foot does a furnace need in Ontario?

In the GTA’s climate, a common rule of thumb is roughly 30–60 BTU/hr per square foot, depending on your home’s age and insulation. Older, less-insulated homes need more BTUs per square foot than newer, tighter builds.

What happens if my furnace or AC is the wrong size?

Oversized equipment short-cycles — turning on and off too often — which wastes energy, wears out parts faster, and leaves your home with uneven temperatures and poor humidity control. Undersized equipment runs constantly and still can’t keep up on the coldest or hottest days. Both mistakes cost you comfort and money.

Do sizing tables replace a professional load calculation?

No. These tables are a starting point, not a final answer. Your actual furnace or AC size depends on insulation, window count and orientation, ceiling height, duct design, and local climate — all of which a Manual J load calculation captures and a table can’t. Every Empower Home Comfort quote starts with a free, no-obligation in-home assessment to get this right.

Do you offer free furnace and AC sizing consultations across the GTA?

Yes — we provide free in-home assessments across Toronto, Etobicoke, North York, Scarborough, Mississauga, Vaughan, Richmond Hill, Markham, Barrie, Hamilton, Oshawa, and Pickering.

Ready For An Exact Number? Get Your Free In-Home Estimate

Skip the guesswork — a licensed Empower Home Comfort technician will assess your home and give you the exact furnace or AC size you need, free of charge.