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Plan a new heat pump, or an air conditioner and furnace, from your house to a shortlist: the loads, the capacity range to shop for, certified systems that fit, the running cost and the next steps.

Method reviewed October 26, 2026. Version 1.0.0. How it works

This is an estimate. It uses a simplified method and typical assumptions, all listed below. Use it to plan and to check quotes; equipment should be sized from a full room-by-room load calculation (ACCA Manual J) by a qualified professional.

Your inputs

Unit system
Compressor type you are considering

Sets the recommended cooling-size range: variable-speed equipment can be sized larger because it slows down at part load.

Stories above grade

Representative design conditions for each IECC climate zone. Choose Custom to enter your local values.

12–18 % is common for houses.

Million BTU (MMBtu) per year, best taken from a year of heating bills: therms × current AFUE ÷ 10. The default is only an example.

Example value; local utility programs often publish a figure for your area.

Result

Cooling load
27,341BTU/h
Heat loss at 16 °F
40,969BTU/h
Estimated running cost per year
$1,249

Cooling load about 27,341 BTU/h (2.28 tons) and heat loss 40,969 BTU/h. Look for 24,607–35,543 BTU/h of cooling capacity, and as much heating capacity at 16 °F as you can get toward 40,969 BTU/h.

  • Your design temperature is 17 °F or colder. Compare capacity at 5 °F and the backup heat each system needs, and consider ENERGY STAR cold-climate models (NEEP sizing guide).
  • Loads are a screening estimate. Before buying, ask for a room-by-room ACCA Manual J load calculation and equipment selection to Manual S.

Capacity to shop for

Cooling capacity to look for — from
24,607BTU/h
Cooling capacity to look for — up to
35,543BTU/h
Nearest common size
2.5tons
Heat pump heating capacity needed at 16 °F for no backup
40,969BTU/h

Running cost per year

Heating
$862
Cooling
$388
Show the working
  1. Block load (same engine as the HVAC Load and AC Tonnage estimators)
    cooling 27,341 BTU/h; heating 40,969 BTU/h at 16 °F outdoors
  2. Recommended cooling capacity for variable-speed equipment: 90–130 % of the load
    24,607 – 35,543 BTU/h
  3. For a heat pump to carry the house alone, its capacity at the design temperature must reach the heat loss
    40,969 BTU/h at 16 °F
  4. Running cost (same method as the Annual Operating Cost Calculator)
    About $1,249 a year ($104 a month on average): $862 heating, $388 cooling.

How the planner works

  • Your house: floor area, climate, insulation, windows and ducts give a heating and cooling load, with the same engine as our HVAC Load and AC Tonnage estimators.
  • The capacity to shop for: the recommended range from the ENERGY STAR National HVAC Design Report, which follows ACCA Manual S — 90–115 % of the cooling load for single-stage equipment, up to 120 % for two-stage and 130 % for variable-speed, and 100–140 % of the heat loss for a furnace.
  • Certified systems that fit: for heat pumps, one click opens the ENERGY STAR comparison with your range and loads, and shows each system’s cooling sizing and the backup heat it would need at your design temperature.
  • Running cost: from the efficiency ratings and energy prices you enter.
  • Then itemise quotes, check incentives and plan financing.

Heat pump or air conditioner and furnace

A heat pump both heats and cools. In cold climates the question is how much of the heating load it can carry at your design temperature, and how much backup heat it needs below its balance point — the comparison shows both for every certified system. An air conditioner with a gas furnace is sized separately for cooling and heating; ENERGY STAR currently lists no certified central air conditioners and does not publish furnace capacities, so for that path the planner gives the ranges to shop for rather than a list of models.

A plan, not a final design

The loads are a screening estimate for the whole house. Before buying, ask your contractor for a room-by-room ACCA Manual J load calculation and equipment selected to Manual S, and compare quotes on the same scope. The planner gives you the numbers to check that work against.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

System you are planning
Ducted heat pump
Compressor type you are considering
Variable speed
Conditioned floor area
2,000 ft²
Stories above grade
1 story
Average ceiling height
8 ft
Climate
Zone 4 — mixed (e.g. Baltimore)
Insulation & air sealing
Average (code-built 1990s–2000s)
Window type
Double pane, clear
Window area (% of floor area)
15 %
Foundation
Slab on grade
Duct location
Attic/crawl — typical
Occupants
4
Target SEER2
17
Target HSPF2
8.5
Annual heat needed (delivered)
40
Full-load cooling hours per year
1,200 h
Electricity price
0.183 $/kWh

Result

Cooling load
27,341 BTU/h
Heat loss at 16 °F
40,969 BTU/h
Estimated running cost per year
$1,249

Cooling load about 27,341 BTU/h (2.28 tons) and heat loss 40,969 BTU/h. Look for 24,607–35,543 BTU/h of cooling capacity, and as much heating capacity at 16 °F as you can get toward 40,969 BTU/h.

Assumptions

  • Indoor design conditions are 70 °F for heating and 75 °F for cooling (ACCA Manual J defaults).
  • The house is modelled as a square footprint with two 20 ft² doors; homes with complex shapes have more wall area and a somewhat higher load.
  • Opaque surfaces use an equivalent temperature difference for sun-heated surfaces: walls +10 °F, ceilings under a vented attic +30 °F.
  • Window solar gain uses an all-orientation average of 60 BTU/h·ft² (calibrated so typical results fall in the range published Manual J studies report) multiplied by the window SHGC and an interior-shading factor of 0.7.
  • Summer air leakage is taken as half of the winter natural air-change rate.
  • Each occupant adds 230 BTU/h sensible and 200 BTU/h latent heat; appliances and lighting add 1,200 BTU/h.
  • Duct losses are a fixed percentage of the sensible load depending on duct location (0 %, 10 %, 20 % or 30 %).
  • Recommended capacity ranges are those in the ENERGY STAR National HVAC Design Report (from ACCA Manual S): cooling 90–115 % of the load for single-stage, 90–120 % two-stage, 90–130 % variable-speed equipment; furnace output 100–140 % of the heat loss.
  • Running costs use the Annual Operating Cost Calculator’s method with the ratings and prices you enter.

Limitations

  • Heat pumps in heating-dominated climates may be sized above the cooling range to cover more of the heating load (ENERGY STAR allows this under Manual S “Condition B”); use the balance point to judge the trade-off.
  • Certified ratings are at standard test conditions, not at your design conditions.
  • Equipment is matched only from ENERGY STAR-certified heat pumps; central air conditioners and furnaces cannot be matched by capacity from the public data.

Frequently asked questions

What size heat pump do I need?

Enough cooling capacity to fall in the recommended range for its compressor type — for a variable-speed unit, 90–130 % of the cooling load — and, in a cold climate, as much heating capacity at your design temperature as you can get toward the heat loss. The planner calculates both and the comparison shows which certified systems fit.

Why is a bigger system not better?

An oversized air conditioner or heat pump short-cycles in cooling, removes less moisture and wears faster. The recommended ranges exist to prevent that; variable-speed equipment tolerates more oversizing because it slows down.

Does it pick a brand for me?

No. It shows certified systems from the ENERGY STAR data that match the capacity range, exactly as certified, and lets you sort and compare them. It does not recommend brands or installers.

Can I get a report of my plan?

Yes. The PDF report includes your inputs, the loads, the capacity ranges, the running cost and the working.

Sources

  1. National HVAC Design Report, Version 3/3.1/3.2 (Rev 13, historical) — ENERGY STAR (U.S. EPA). Equipment sizing limits from ACCA Manual S: cooling 90–115 % (single-speed), 90–120 % (two-speed), 90–130 % (variable-speed) recommended; furnace 100–140 % recommended.
  2. Manual J — Residential Load Calculation — Air Conditioning Contractors of America (ACCA). Manual J is the ANSI-recognised standard for residential equipment-sizing loads required by building codes.
  3. Guide to Sizing & Selecting Air-Source Heat Pumps in Cold Climates (rev. 04/08/20) — NEEP (hosted by U.S. DOE Building Science Education Solution Center). Size from the manufacturer’s extended performance (maximum capacity) data; ccASHP maximum capacities at 5 °F can corroborate it; avoid outdoor units whose minimum capacity exceeds the smallest indoor unit’s need.
  4. ENERGY STAR Certified Heat Pumps (dataset 83eb-xbyy) — U.S. EPA (public domain). Certified systems with SEER2, EER2, HSPF2, heating capacity at 47/17/5 °F and COP at 5 °F; 47 °F and 5 °F values come from different tests.
  5. Proper Sizing of HVAC Systems — U.S. DOE Building Science Education Solution Center. Rules of thumb lead to oversized systems; loads should be calculated with Manual J.

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