Heating Btu Calculator – How Many Btu Per Square Foot Do I Need?

How many btu to heat 1000 sq ft? How many square feet will 30,000 BTU heat? You can get more accurate answers thourgh our BTU heating calculator.

Our goal is to help you determine the right size furnace/heater for your heating requirements. It is based on the needed heating BTU per square foot for most homes and your climate.

Our heating BTU calculator takes those very important factors into account, so, for example, if you have a question like, “how many BTU do I need to heat 1,500 square feet? The quick answer is 60,000-80,000 BTUs based on different climate zones.

The BTU per square foot heating rule of thumb varies widely based on your climate and the size of the house or space you want to heat.

How Many BTU of Heating Per Square Foot Do I Need?

That’s an important question to get a right answer to. A furnace or space heater that is too small won’t adequately heat your home on the coldest winter days. Rooms furthest from the heater might become uncomfortably cool spots in your house.

A furnace that is too large will waste energy and create warm spots at grates near the furnace before the cycle ends.

The generally accepted BTU per square foot heating rule of thumb ranges from 30 BTU to 60 BTU per square foot. That’s a wide difference, essential one furnace being twice as large as the other, so the size factors are discussed to help you narrow down the right BTUs needed for your home. 

This list showing heating BTU per square foot is taken from our PickHVAC Furnace Ultimate Guide:

  • Zones 1 & 2 (hot): 30-35 Btu/sq. ft.
  • Zone 3 (warm): 35-40 Btu/sq. ft.
  • Zone 4 (moderate): 45 Btu/sq. ft.
  • Zone 5 (cool): 50 Btu/sq. ft.
  •  Zone 6 (cold): 55 Btu/sq. ft.
  • Zone 7 (very cold): 60 Btu/sq. ft.

The Zones are shown in the map below. There are factors other than climate, and they are used in our heating BTU calculator below to give you the most accurate information.

Example: With 75,000 BTU heater, you can heat a 2,500 sq ft house in Florida. If you’re living in New York, a 75,000 BTU furnace would only heat a 1,500 sq ft home.

Heating BTU Calculator

OK, there is more information below.

Let’s start with this very useful map. It was developed by the International Code Council / International Energy Conservation Code and adopted by the US Department of Energy’s Office of Energy Efficiency & Renewable Energy.

We mention that to represent it as accurate and very useful for our purposes.

Heating BTU Calculator

Heating Btu Calculator

Locate your climate zone on the map above and provide your square footage. You'll get how many BTUs needed for your heating system.

See the climate zone map above to find your home's climate zone

See local cost of
30,000 BTU Heating Unit

Calculate heating BTU needed in four easy steps.

1. Climate Zone: Find your location on the map. Pro tip: If you’re on or near the border between Zones, choose the higher number/cooler Zone.

2. Home Size: Enter the square footage of your home. If you don’t know it, the information might be found on a blueprint or house drawing, in closing documents or similar. If you don’t have any of those, the easiest way to determine it is to measure rectangles within your home – multiplying width x length for each if there are more than one – and adding their totals.

3. Insulation: There are two keys to insulation – How well your home is sealed and the type and thickness of the insulation. In terms of being sealed, is your home’s exterior covered in house wrap like Tyvek? It’s also called vapor barrier. It is now code, so if your home doesn’t have it, vapor barrier/wrap will have to be installed the next time you replace the siding.

Are the windows and doors newer and in good condition? If you answer “yes” to the house wrap and window/doors questions, then choose Good or Average in the Insulation box. If you don’t know, if your home is older and hasn’t been remodeled, or if you can feel drafts coming in around windows and doors, choose Poor.

Money Saving Tip: Adding attic insulation to an attic that is inadequately insulated is the #1 best way to lower your heating bills and get the best return on investment. In fact, the prestigious Remodeling Magazine annual survey consistently shows that attic insulation has a 105% to almost 120% return on investment (Cost vs. Value). In other words, the money spent will be quickly gained back through lower energy bills.

The image below shows how much attic insulation your home should have.

how much attic insulation

4. Sun Exposure: Climate and the trees around your home factor into this box. If your home is surrounded by tall trees that shade the walls and the roof – and few are – then choose Heavily shaded. Most homes, in this regard, are either Average or Very Sunny.

But “Very Sunny” means something very different in Denver (245 days with sun) than it does in Portland, Oregon (142 days with sun), even if there are no shade trees around the house. Therefore, consider the map below. The deeper the color, the more sunny the climate. In Minnesota, a home with no shade would still only be Average for sun exposure, for example.

Annual Sunshine

Make your choice and enter data for each box, and let the heating BTU calculator do the work.

Here is an example how to use the above calculator:

Let’s say you have a 2,500 sq ft two-story home in Chicago. Your house was built in 2005 with a “good insulation”. You should choose “Average Sun Exposure” and “Zone 5” based on the Climate Zone Map and Sun Exposure Map. 

After you enter all the data, you will get 90,000 BTUs from the calculator.

Chart of Recommended Heating BTU Per Square Foot

This chart begins small – space heater size, not furnace size – and progresses to homes in the average to large size category. You can use it to answer the common questions like:

  • How many btu for 600 sq ft? It’s around 30,000 BTU.
  • How many btu do I need to heat 1,500 square feet? It’s 70,000 – 80,000 BTU.
  • What size furnace to heat 2,000 square feet? You need a 90,000-110,000 BTU furnace.
  • How many btu do I need to heat 3,000 square feet? 150,000+ BTU furnace is a better option.
Room/Area SizeHeating Capacity(BTU)Examples
100 sq ft4,000-6,000 BTU10x10 room, 10x12 room, Small den or office
200 sq ft9,000-11,000 BTU10x20 room, 12x12 room, 15x15 room
300 sq ft12,000-16,000 BTUEfficiency apartment. 12x24 garage
400 sq ft18,000-22,000 BTU20x20 room or garage
500 sq ft22,000-27,000 BTUStudio/1-bedroom apartment, Tiny house
600 sq ft27,000-33,000 BTU20x30 room, 24x24 garage
700 sq ft31,000-38,000 BTU24x30 garage, 1 or 2-bedroom townhouse
750 sq ft34,000-41,000 BTU26x30 garage, 1 or 2-bedroom townhouse
800 sq ft36,000-44,000 BTUSmall home, 2-3 bedroom apartment
900 sq ft40,000-49,000 BTU30x30 garage
1,000 sq ft45,000-55,000 BTUSmall home, 2-3 bedroom apartment
1,200 sq ft55,000-65,000 BTU30x40 garage, 3 bedroom townhouse
1,300 sq ft59,000-71,000 BTUSmall/Average home, large apartment
1,400 sq ft63,000-77,000 BTUSmall/Average home, large townhouse
1,500 sq ft68,000-82,000 BTU40x40 garage, average home
1,600 sq ft72,000-88,000 BTUAverage home, large townhouse or home addition
1,700 sq ft77,000-93,000 BTUAverage home, large townhouse or apartment
1,800 sq ft81,000-99,000 BTUAverage home, large townhouse or apartment
2,000 sq ft90,000-110,000 BTUAverage home, large townhouse, guest house
2,200 sq ft100,000-120,000 BTUAverage home, 4-bedroom apartment
2,400 sq ft108,000-132,000 BTUAverage to large home, very large townhouse
2,500 sq ft113,000-137,000 BTUAverage to large home, very large townhouse
3,000 sq ft135,000-165,000 BTULarge home, one zone in a very large home

At some point, depending on the climate, you have to begin to think about more than one heating device – furnace, boiler, heat pump, etc., for your home. You can still use this chart for very large homes by considering the size of the zones in your home. 

For example, if the bedroom and office area zone is 1,800 square feet and the living areas and kitchen are 2,400 square feet, add together the recommended BTUs for each. You’ll need between about 180,000 and 280,000 total BTUs for your home based on the climate and house factors considered in the calculator. 

Pro Tip: For smaller rooms/zones/apartments, a ductless mini split heat pump is another really good option. They’re efficient and come with potential lower installation costs than furnaces.

How Many Square Feet Will 4,000 – 80,000 BTU Heat?

If you already bought a specific size space heater or furnace and want to know the square footage it can heat, here are the quick answers:

Heating CapacitySquare Footage(Hot Climate)Square Footage(Moderate Climate)Square Footage(Cold Climate)
4,000 BTU130 sq ft85 sq ft70 sq ft
5,000 BTU160 sq ft110 sq ft90 sq ft
6,000 BTU200 sq ft130 sq ft105 sq ft
9,000 BTU300 sq ft200 sq ft160 sq ft
10,000 BTU320 sq ft220 sq ft180 sq ft
11,000 BTU350 sq ft240 sq ft200 sq ft
12,000 BTU400 sq ft260 sq ft200 sq ft
15,000 BTU500 sq ft320 sq ft270 sq ft
16,000 BTU530 sq ft350 sq ft290 sq ft
20,000 BTU600 sq ft430 sq ft360 sq ft
30,000 BTU1,000 sq ft600 sq ft500 sq ft
40,000 BTU1,320 sq ft880 sq ft700 sq ft
60,000 BTU2,000 sq ft1,300 sq ft1,100 sq ft
75,000 BTU2,500 sq ft1,600 sq ft1,300 sq ft
80,000 BTU2,700 sq ft1,800 sq ft1,450 sq ft

For example, a 30,000 BTU space heater will heat 1,000 square feet in Florida, which is in hot climate. You can only heat 600 sq ft if you are living in cold climate. 

For most areas, 40,000 BTU will heat 800 square feet. But if you live in very south, it can heat more than 1,000 sq ft.

BTUs: Definition and Ratings

A BTU is a measurement of heat – specifically, the heat needed to raise the temperature of one pound of water 1 degree Fahrenheit. The full name is British thermal unit.

It is an exact measurement that can be applied to most heating equipment. The correct rating is BTU/hour, or BTU/h, meaning how much heat does the equipment create in one hour of constant operation.

Furnaces rarely run for an hour straight, but that’s how they are rated.

Did you Know? BTU ratings are also used for air conditioning. The rating for ACs isn’t, obviously, the amount of heat the equipment creates, but the heat that it removes from a room each hour.

And for heat pumps, it is the same as for air conditioners – the amount of heat moved from outside to inside during heating.

Our guide How Many BTU Air Conditioner Do I Need? explains how BTUs apply to air conditioners and, to some extent, heat pumps.

How Many BTU Do Furnaces Make? Standard Boilers?

It’s a wide range. The smallest gas furnaces start at about 30,000 BTU per hour, or BTU/h.

While BTU/h, how many BTUs of heat the unit can create in one hour, is the technical specification, most heating equipment such as propane, oil and gas furnaces are rated simply by BTUs or BTU.

The most common sizes are from about 70,000 to 120,000 BTU/h.

The largest gas furnaces create about 140,000 BTU/h.

Oil furnaces have a slightly different range from about 60,000 to 160,000 BTU/h.

What About Wood Stove/Boilers and Combi Boilers?

Both of these heating equipment types provide both hot water for heat and water used to heat water in your hot water tank. The second half of that sentence is a mouthful – wood-burning combi boilers heat water – but that hot water doesn’t flow directly into your hot water pipes. Instead, it circulates through a pipe in your hot water tank to provide you with what is called “domestic” hot water. This type of heating equipment is growing in popularity, especially where free or cheap wood is readily available. See our Wood Furnace/Boiler Reviews and Buying Guide for details.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree from Lone Star College and EPA & R-410A Certifications.

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