How many BTU do I need to heat 1,000 square feet?

45,000-50,000 BTU/h in zone 4 with average insulation, 47,500 BTU/h at the midpoint. Across the zones the rule gives 1,000 sq ft between 30,000 BTU/h (zone 1) and 60,000 BTU/h (zone 5), HVACDirect.com, How to Size Your Air Conditioner or Heater, heating factor. The guide on this site has the full grid by home size and zone.

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

In zone 4 with average insulation, 95,000 BTU/h at the midpoint, which is 7.92 tons: the tool rounds that up to a class of 8 tons. In zone 5 the same home is 9.17 tons; in zone 1, 5.42 tons. Heat pump capacity falls as the outdoor temperature drops, so an installer sizes to the local design temperature, not to this rule.

Which climate zone is my state in?

Pick the state in the tool and it sets the zone: Zone 1, hot (south Florida, Hawaii); Zone 2, warm (the Gulf and Deep South, Arizona, southern California); Zone 3, moderate (Carolinas, Tennessee, Virginia, Oklahoma); Zone 4, cool (Midwest, Mid-Atlantic, Pacific Northwest); Zone 5, cold (northern tier, New England, Alaska). The assignment is ours, read from the regional descriptions in the sources, and border states can go either way; the zone list lets you override it.

Furnace or heat pump: is the BTU figure the same?

The heating load is the same figure: it describes the house, not the equipment. A gas furnace is rated by its output in BTU/h (the tool rounds up to the next 10,000), a heat pump by tons (rounded to the next half ton); a heat pump also cools, so its size is checked against the cooling load too, which the AC calculator and the Pro report give room by room.

What is a Manual J and why does it replace this?

Manual J is the ACCA residential load calculation installers use: it counts every wall, window, door, the orientation, the air leakage and the local design temperatures to get the heating and cooling loads. The BTU-per-square-foot rule here is a published shortcut for a first estimate and a sanity check on a quote; it is not a substitute for the calculation.

Free calculator

Heat pump / furnace size calculator (US, by climate zone)

A 2,000 sq ft home in zone 4 with average insulation needs 90,000-100,000 BTU/h of heating on the published BTU-per-square-foot rule: 95,000 BTU/h at the midpoint, 7.92 tons, 27.84 kW, a furnace of 100,000 BTU/h output or a heat pump of 8 tons. Pick your state or zone, type your area and insulation to see yours.

Region and unitsSwitching region converts your dimensions; the charts are the same. Your numbers stay in this browser only.Home floor area (sq ft)sq ftStarting value: Bryant, What Size Furnace Do I Need?, read 2026-09-20; edit it.

US state (sets the zone)Climate zone

Starting value: BTUtally starting example, read 2026-09-20; edit it.

Insulation

Poor insulation +10 %, good -10 % (Inch Calculator, Furnace BTU Calculator).

Result

Heating load (midpoint): 95,000 BTU/h
Range for the zone: 90,000-100,000 BTU/h
Tons: 7.92 tons
Kilowatts: 27.84 kW
Furnace class: 100,000 BTU/h output
Heat pump class: 8 tons

2,000 sq ft x 45-50 BTU per sq ft (zone 4, HVACDirect.com, How to Size Your Air Conditioner or Heater, heating factor). Rule of thumb: a Manual J calculation by an installer replaces it. The classes are the load rounded up to the next 10,000 BTU/h and the next half ton, not a product list. Sizing estimates from published charts and rules of thumb (ENERGY STAR, manufacturer guides), each with its source and date: a Manual J load calculation by an installer is the final word.

Sizing the whole home? Pro puts every room on one printable report.

A room list with cooling BTU per room and the totals, the heating load, the boiler kW and the equipment classes, with the sources. Printed or exported to Excel.

See Pro

How it works

Heating load = floor area in sq ft x BTU per hour per sq ft for the climate zone (zone 1 30-35, zone 2 35-40, zone 3 40-45, zone 4 45-50, zone 5 50-60), a range published by HVAC suppliers and manufacturers. Poor insulation multiplies the range by 1.1, good insulation by 0.9. The single figure carried into the report is the midpoint of the adjusted range. Tons = BTU/h / 12,000; kW = BTU/h / 3,412. The furnace class is the midpoint rounded up to the next 10,000 BTU/h of output and the heat pump class to the next half ton: rounding, not a product list.

The zone is most of the answer: the same 2,000 sq ft home needs 65,000 BTU/h in Florida (zone 1) and 110,000 BTU/h in Minnesota (zone 5), against 95,000 BTU/h in zone 4. Poor insulation in zone 4 takes it to 104,500 BTU/h; a 1,000 sq ft home in zone 4 needs 47,500 BTU/h.

The state list sets the zone by where most of the state's people live, read off the published maps (BTUtally's reading of the published five-zone heating maps, by where most of each state's people live); the sources place border states differently and a mountain county can sit a zone colder than the coast, so pick the zone directly if you know it. All of it is a rule of thumb: a Manual J load calculation by an installer, which counts windows, orientation, air leakage and the local design temperature, replaces it before equipment is bought.

Every number is yours to change; all calculations run in your browser and the inputs stay there, so the Pro report can pick up your heating load. Sizing estimates from published charts and rules of thumb (ENERGY STAR, manufacturer guides), each with its source and date: a Manual J load calculation by an installer is the final word.

Sources of the starting values

BTU per sq ft by climate zone: HVACDirect.com, How to Size Your Air Conditioner or Heater (read 2026), heating factor: "Zone 1: 30 - 35 Btu's per square foot", "Zone 2: 35 - 40", "Zone 3: 40 - 45", "Zone 4: 45 - 50", "Zone 5: 50 - 60". Inch Calculator, Furnace BTU Calculator (undated): the same five rows, "Zone 1 (hot) 30-35 BTU/sq. ft." to "Zone 5 (cold) 50-60 BTU/sq. ft."; InspectAPedia, BTU Requirements in U.S. Climate Zones: the same table. Bryant, What Size Furnace Do I Need? (read 2026), by region: "Warm (South/Southwest) 30-35 BTUs", "Moderate (Midwest/Mid-Atlantic) 40-50 BTUs", "Cold (Northeast/Northern Midwest) 50-60 BTUs" per sq ft. Rule of thumb: "a Manual J calculation replaces it" — https://hvacdirect.com/sizing-air-conditioner-and-heater.html and https://www.inchcalculator.com/calculate-btus-to-heat-home/ and https://inspectapedia.com/heat/Heating-Cooling-Climate-Zone-BTU-Requirements.php and https://www.bryant.com/en/us/products/gas-furnaces/what-size-furnace-do-i-need/, read on 2026-09-20
Insulation adjustment: Inch Calculator, Furnace BTU Calculator (undated, read 2026): poorly insulated homes require "10% more BTUs due to heat loss"; well-insulated homes need "10% fewer BTUs to heat". Bob Vila, What Size Furnace Do I Need? (updated 2022-04-07): newer homes with quality insulation use the lower end of the zone's range, older homes "using the higher range is recommended" — https://www.inchcalculator.com/calculate-btus-to-heat-home/ and https://www.bobvila.com/articles/what-size-furnace-do-i-need/, read on 2026-09-20
State to zone: BTUtally's reading of the published five-zone heating maps, by where most of each state's people live: InspectAPedia (regional examples: "Tip of Florida" zone 1; "Most of Florida, Southern Texas, South Georgia" zone 2; "Central Texas, Central Georgia, South Carolina... most of California" zone 3; "North Texas Panhandle, Washington State, Southern Michigan, Southern New York, Virginia, North Georgia" zone 4; "most of Pennsylvania... Boston area" zone 5), Bryant (Warm = South/Southwest, Moderate = Midwest/Mid-Atlantic, Cold = Northeast/Northern Midwest) and Bob Vila (Zone 1 "southern Texas and most of Florida"; the coldest zone "northern Wisconsin and most of Maine"). The sources place border states differently: if you know your zone, pick it directly — https://inspectapedia.com/heat/Heating-Cooling-Climate-Zone-BTU-Requirements.php and https://www.bryant.com/en/us/products/gas-furnaces/what-size-furnace-do-i-need/ and https://www.bobvila.com/articles/what-size-furnace-do-i-need/, read on 2026-09-20
Starting home: Bryant, What Size Furnace Do I Need? (read 2026): the guide's worked example is a 2,000 sq ft home, "60,000-120,000 BTUs, depending on insulation and climate"; Inch Calculator uses the same 2,000 sq ft example ("between 80,000 and 90,000 BTUs" in a moderate climate); type your own area — https://www.bryant.com/en/us/products/gas-furnaces/what-size-furnace-do-i-need/ and https://www.inchcalculator.com/calculate-btus-to-heat-home/, read on 2026-09-20
Tons and kW: Wikipedia, British thermal unit (read 2026): "1 ton of cooling, a common unit in North American refrigeration and air conditioning applications, is 12,000 Btu/h (3.52 kW)" — https://en.wikipedia.org/wiki/British_thermal_unit, read on 2026-09-20
BTU/h to watts: Wikipedia, British thermal unit (read 2026): "1 W is approximately 3.412142 Btu/h"; the International Table BTU is about 1,055.06 J — https://en.wikipedia.org/wiki/British_thermal_unit, read on 2026-09-20

The UK / metric setting takes m² and shows kW first; the zones are US zones, so for a UK home use the boiler calculator instead.

Frequently asked questions

How many BTU do I need to heat 1,000 square feet?: 45,000-50,000 BTU/h in zone 4 with average insulation, 47,500 BTU/h at the midpoint. Across the zones the rule gives 1,000 sq ft between 30,000 BTU/h (zone 1) and 60,000 BTU/h (zone 5), HVACDirect.com, How to Size Your Air Conditioner or Heater, heating factor. The guide on this site has the full grid by home size and zone.
What size heat pump do I need for a 2,000 sq ft house?: In zone 4 with average insulation, 95,000 BTU/h at the midpoint, which is 7.92 tons: the tool rounds that up to a class of 8 tons. In zone 5 the same home is 9.17 tons; in zone 1, 5.42 tons. Heat pump capacity falls as the outdoor temperature drops, so an installer sizes to the local design temperature, not to this rule.
Which climate zone is my state in?: Pick the state in the tool and it sets the zone: Zone 1, hot (south Florida, Hawaii); Zone 2, warm (the Gulf and Deep South, Arizona, southern California); Zone 3, moderate (Carolinas, Tennessee, Virginia, Oklahoma); Zone 4, cool (Midwest, Mid-Atlantic, Pacific Northwest); Zone 5, cold (northern tier, New England, Alaska). The assignment is ours, read from the regional descriptions in the sources, and border states can go either way; the zone list lets you override it.
Furnace or heat pump: is the BTU figure the same?: The heating load is the same figure: it describes the house, not the equipment. A gas furnace is rated by its output in BTU/h (the tool rounds up to the next 10,000), a heat pump by tons (rounded to the next half ton); a heat pump also cools, so its size is checked against the cooling load too, which the AC calculator and the Pro report give room by room.
What is a Manual J and why does it replace this?: Manual J is the ACCA residential load calculation installers use: it counts every wall, window, door, the orientation, the air leakage and the local design temperatures to get the heating and cooling loads. The BTU-per-square-foot rule here is a published shortcut for a first estimate and a sanity check on a quote; it is not a substitute for the calculation.