Cooling Load
36,500
BTU/hr
Tonnage
3.0
ton
Range: 3.0 – 3.5 ton
Heating Load
60,000
BTU/hr
System Type
Central AC or heat pump
Standard central system — most single-family homes
How we calculated this
× 1 (moderate climate)
× 1.00 (8ft ceiling ÷ 8ft)
× 1 (2 stories)
× 1 (built 1990–2009)
× 1 (average insulation)
× 1 (window-to-wall average (10–20%))
× 1 (mixed orientation)
= 36,000 BTU
= 60,000 BTU/hr
Simplified Manual J estimate. For code-compliant sizing, consult a licensed HVAC contractor.
Reference
Whole-Home Sizing by Climate
Estimates based on 2-story construction, 8 ft ceilings, 1990–2009 build, average insulation and window ratio, 3 occupants. Adjust 15–20% up for poor insulation or ducts in an unconditioned attic.
| Home Size | Hot Climate | Moderate | Cold Climate |
|---|---|---|---|
| 1,000 sq ft | 2 ton | 1.5 ton | 1 ton |
| 1,500 sq ft | 3 ton | 2.5 ton | 1.5 ton |
| 2,000 sq ft | 4 ton | 3 ton | 2 ton |
| 2,500 sq ft | 5 ton | 4 ton | 2.5 ton |
| 3,000 sq ft | 6 ton | 4.5 ton | 3 ton |
| 3,500 sq ft | 7 ton | 5.5 ton | 3.5 ton |
Learn
Understanding Whole-Home HVAC Sizing
Room BTU vs. whole-home load
A room BTU calculation sizes one space on its own. Useful for a window AC or a mini-split. A whole-home load sizes the whole house. And it isn't the sum of your rooms. The number usually comes in lower than that, because interior walls don't count the way exterior ones do.
Manual J, and what we leave out
ACCA Manual J is the industry standard for residential load calculations, required for permitted installs in most jurisdictions. The full procedure uses your local 99th-percentile design temperatures, measured wall U-values, duct loss factors, and a room-by-room breakdown. This tool approximates that result with rule-of-thumb multipliers. Enough to plan with; not enough to pull a permit.
Construction year
Pre-1970 homes often have R-7 or less in the walls, no vapor barrier, and single-pane windows with daylight visible around the frames. A 2010-or-later home built to IECC 2009 or 2012 might have R-20 walls, an R-49 attic, and double-pane low-E glass. Practically a different physics problem. The construction year input is a proxy for all of that.
Window-to-wall ratio and solar gain
Glass is the weak point of any envelope. Even good double-pane glass at U-0.3 conducts heat about six times faster than a well-insulated wall at U-0.05. Put large picture windows on the south and west faces and you can add 10–15% to the cooling load versus the same house with less glass.
Orientation
A home with its long axis running east–west and main windows facing south takes the most direct solar gain, roughly 5% more cooling load than a neutral orientation. North-facing takes the least. This matters most in hot climates and in homes carrying a lot of glass.
Which load dominates
In Florida and along the Gulf Coast, cooling almost always wins: size for cooling and your heating is covered. In Minnesota, New England, and the mountain states, heating dominates. The desert Southwest and moderate climates can go either way, with surprisingly real heating loads on winter nights.
Humidity is part of the cooling load too. In a humid climate the system spends real capacity wringing moisture out of the air, which is why the hot & humid option carries a higher cooling factor than hot & dry even when the thermometer reads the same.
Duct losses this tool doesn't capture
Ductwork routed through an unconditioned attic can lose 10–30% of its conditioned air before it reaches the living space. The calculation assumes none of that. If your ducts run through an unconditioned attic (common in homes built between 1970 and 2000), add about 15% to the result before you shop.
Reading the output
The cooling load is what your AC needs to cover; the heating load is the target for a furnace or heat pump. The tonnage range is your shopping window, anything inside it is a reasonable fit. For a heat pump doing both jobs, size it to the larger of the two loads. Gas furnace paired with central AC, size each to its own number.
FAQ
Common Questions About HVAC Load Sizing
What's the difference between this and the BTU Calculator?
The BTU Calculator sizes a single room. That's the right tool for a window AC, a portable unit, or a single-zone mini-split.
This one sizes the whole house for a central system, so it brings in building-level factors a single room never sees: how many stories you have, when the place was built, the window-to-wall ratio, and which way it faces. Reach for it when you're shopping a central AC, furnace, or whole-home heat pump.
What does "Manual J simplified" mean?
Manual J is the ACCA standard for residential load calculations, and most jurisdictions require it for a permitted install. A full one pulls your local 99th-percentile design temperatures, measured wall U-values, duct loss factors, and infiltration data.
We approximate what a full Manual J measures, with rule-of-thumb multipliers in place of those measured inputs. It's accurate enough to plan around and to shop with. The Manual J your contractor files is what goes on the permit.
Does this calculation account for duct losses?
No. This number is the building's thermal load, not the extra capacity it takes to push conditioned air through leaky ductwork. Ducts in an unconditioned attic can lose 10–30% before the air ever reaches a room, so add about 15% to the cooling result before you shop. Ducts inside the conditioned envelope, or in an encapsulated crawlspace, lose next to nothing.
Why does construction year affect the result so much?
Older homes leak. A house built before 1970 predates modern energy codes: figure R-7 or less in the walls, no vapor barrier, single-pane windows. Build the same floor plan in 2010 under IECC 2009 or 2012 and you get R-20-plus walls, an R-49 attic, and double-pane low-E glass.
That's a different building. Same square footage, 20–30% different load.
My home has been remodeled. What year should I enter?
Enter the original construction year, then set insulation quality to Good to account for what you've done.
The year carries baseline structural details that adding insulation doesn't undo: window framing, wall depth, how the place was air-sealed. The insulation input handles everything you've added to the envelope since.
My contractor quoted a very different size. Who is right?
Trust the contractor's full Manual J over a rule-of-thumb estimate: they're measuring your actual building. A half-ton spread between their number and this one is normal.
A full ton or more is worth a conversation. The HVAC trade has a well-documented habit of oversizing, so if the quote runs noticeably large, ask them to show you the load calculation.
Does this work for heat pumps?
Yes. Heat pumps use the same BTU and tonnage framework, so size for whichever is larger, your cooling load or your heating load. In a cold climate, check the unit's rated capacity at your area's 99% winter design temperature against the heating load shown here. Heat pump output falls off in extreme cold, which is exactly the problem cold-climate models from Mitsubishi, Bosch, and Daikin are built to solve.
Related Tools
BTU Calculator
Size a window AC, portable unit, or mini-split for a single room.
↳ 300 sq ft · hot & humid · sunny → ~12,500 BTU
AC Size Calculator
Quick square-footage to AC tonnage lookup with a reference table.
↳ 1,200 sq ft · moderate → ~2 ton unit
SEER Savings Calculator
Estimate annual savings and payback period when upgrading to a higher-efficiency unit.
↳ SEER 10 → 18 · 3 tons · warm → ~$410/yr saved