What Size Furnace for a 2,000 Square Foot House?
Furnace input, 80% AFUE
112,500 BTU/hr
2,000 square feet, 8 foot ceilings, climate zone 4, sized on 90,000 BTU of heating output.
This is a rule of thumb and it is not a load calculation. The real answer is a Manual J, which counts your windows, your insulation, your infiltration and which way the house faces, and a contractor should run one before anybody orders equipment. Use this number to sanity check a quote, not to place an order.
Oversizing is the classic mistake and it is worse than being slightly small. A unit with too much capacity satisfies the thermostat in a few minutes and shuts off, so it never runs long enough to pull water out of the air, and the house ends up cold and clammy with the compressor short cycling itself to an early grave.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Conditioned floor area2000 sq ft
- Ceiling height8 ft
- Climate zoneZone 4, mixed, mid Atlantic and the lower Midwest
- Sun exposureAverage
- People living there4 each
- Kitchen inside the conditioned spaceYes
Cooling size4 tons
This is a rule of thumb and it is not a load calculation. The real answer is a Manual J, which counts your windows, your insulation, your infiltration and which way the house faces, and a contractor should run one before anybody orders equipment. Use this number to sanity check a quote, not to place an order.
Oversizing is the classic mistake and it is worse than being slightly small. A unit with too much capacity satisfies the thermostat in a few minutes and shuts off, so it never runs long enough to pull water out of the air, and the house ends up cold and clammy with the compressor short cycling itself to an early grave.
| Cooling load | 45,200 BTU/hr |
|---|---|
| That is | 3.77 tons12,000 BTU makes a ton |
| Equipment size to shop for | 4 tonnearest half ton step |
| Cooling per square foot | 23 BTU |
| Heating output needed | 90,000 BTU/hr |
| Furnace input, 80% AFUE | 112,500 BTU/hr |
| Furnace input, 95% AFUE | 94,737 BTU/hr |
The material list this produces
| Condenser, tons | 4 |
|---|---|
| Matched air handler or coil, tons | 4 |
| Line set, ft | 25 |
| Equipment pad, each | 1 |
| Disconnect and whip, each | 1 |
| Programmable thermostat, each | 1 |
Climate zone compared
The same house sizes differently by climate, and not in the direction people expect. Cooling load falls as you go north while heating load climbs, so a Minnesota house needs a smaller air conditioner and a much bigger furnace than a Florida one.
| Climate zone | Cooling size | Heating output needed |
|---|---|---|
| Zone 1 | 4.5 tons | 60,000 BTU/hr |
| Zone 2 | 4 tons | 70,000 BTU/hr |
| Zone 3 | 4 tons | 80,000 BTU/hr |
| Zone 4 | 4 tons | 90,000 BTU/hr |
| Zone 5 | 3.5 tons | 100,000 BTU/hr |
| Zone 6 | 3.5 tons | 110,000 BTU/hr |
| Zone 7 | 3.5 tons | 120,000 BTU/hr |
What else matters here
The number on a furnace label is almost always input, the gas going in, and the number that heats your house is output. An 80 percent AFUE furnace sends a fifth of its input up the flue, so 90,000 BTU of output needs 112,500 of input. The same output from a 95 percent condensing furnace needs 94,737.
This is where furnace quotes stop comparing. A shop quoting a 100,000 BTU 80 percent unit and a shop quoting a 100,000 BTU 95 percent unit are not quoting the same amount of heat: the second delivers 95,000 and the first 80,000, a difference of nearly two rooms.
Oversizing a furnace has the same failure mode as oversizing an air conditioner. It reaches the thermostat setting fast, shuts off, and the house swings between too warm and too cool while the heat exchanger takes the thermal cycling. A two stage or modulating furnace is the usual answer where the load varies a lot through the season.
What this calculator assumes
- This is the square foot method, the same rule of thumb behind every free sizing chart: 20 BTU per square foot of cooling as the base, scaled for ceiling height, climate zone and sun, plus 600 BTU for each person over two and 4,000 for a kitchen.
- Heating is figured at 30 to 60 BTU per square foot depending on zone, which is output at the register. Furnace input is higher, because an 80 percent furnace throws a fifth of the gas up the flue.
- Equipment is sold in half ton steps up to 5 tons, so the number to shop with is the rounded one, not the raw one.
Questions people ask
What size furnace do I need for 2,000 square feet?
About 90,000 BTU of output in a mixed climate. That is a 112,500 BTU input at 80 percent AFUE, or 94,737 at 95 percent. Shops stock them in 20,000 BTU steps, so expect a quote for a 100,000 or a 120,000.
What is the difference between furnace input and output BTU?
Input is the gas the burner consumes, output is the heat that reaches the ducts. AFUE is the ratio between them. Labels and quotes usually give input, which is why two furnaces with the same number on the box can deliver very different amounts of heat.
Is this the same as a Manual J?
No. A Manual J counts the actual windows and which way they face, the insulation in the walls and the attic, how tight the envelope is, the duct losses and the local design temperature. Two houses of identical size can be a ton and a half apart on that calculation. Use this figure to check whether a quote is in the right range, then have the load calculation done before anything is ordered.
The btu and ac size calculator takes any dimensions you like and hands back the same list.