Electric Furnace Size Calculator: What Size Electric Furnace Do I Need?

This electric furnace sizing calculator gives you accurate information about the right size furnace for your home based on critical factors – Local climate, home size, insulation levels in your home and the amount of sun exposure your home receives.

It is simple to use and gives the most accurate results of any electric furnace calculator.

Wire Size, Amps and Breaker Size too: The electric furnace size calculator goes beyond a kW – kilowatt – recommendation and provides electrical specifications for wire size and breaker amps. That important information is what sets the Pick HVAC electric furnace sizing calculator apart from others.

Let’s start with the calculator and step-by-step instructions for sizing an electric furnace – that is, we walk you through using the calculator. Jump right in if you’re familiar with these types of calculators, or use our guidance to make sure you get it right.

Below the sizing calculator is an electric furnace sizing chart, BTU to kW conversion chart and more information to assist in deciding if an electric furnace is the right choice for your home.

Electric Furnace Sizing Calculator

What size electric furnace do I need? That’s a question we get frequently, and that’s why we designed this electric furnace size tool.

Electric Furnace Sizing Calculator

Step 1 – Climate Zone

Zones 5-7 Beware! While we include all the Climate Zones, Pick HVAC does not recommend the use of an electric furnace in Zones 5-7. They are not a cost-effective means of heating a home in cold regions. Your electricity bills will soon outweigh any cost savings you enjoyed on the equipment compared to buying a gas furnace.

In Zone 5, you might also consider a heat pump that delivers heat in winter and cooled/dehumidified air in summer. Of all common HVAC systems, a heat pump is the most energy efficient.

Near the Edge of a Zone? We recommend choosing the colder Zone – the Zone with the higher number. You’ll end up with a larger furnace – one with more kW/BTU capacity. The extra cost for the furnace will be small, and you’ll have the heating power you need on the coldest winter days.

Step 2 – Home Size in Square Feet

How large is the space you intend to heat? Click/choose the box, and type in the number of square feet. The Up/Down arrows can be used too.

How to measure square footage: You might be able to skip the measurement if you have a blueprint or drawing for your home or the square footage is listed on closing documents you received when you purchased/built the home. Otherwise:

Option 1: Measure the length x width of each room or zone. Write down each result, and add them all together. If a room is L-shaped, measure each rectangle separately, and add them.

Option 2: From outdoors, measure the footprint of your home.

Step 3 – Insulation Condition

What we say in our Heat Pump Sizing Calculator guide is true for electric furnaces too.

Consider insulation in these categories:

Good: Your home is fairly new, or it has been updated with house wrap, increased insulation in the attic and/or new energy efficient doors and windows.

Average: Your home is vintage 1990 to 2010, and not much has been done to make it more energy efficient. The “average” rating would also apply to a home built before 1990 with some energy efficient updates in place such as added insulation or better windows.

Poor: Your home is old and hasn’t been updated. Windows and doors are drafty, and some rooms are colder than the rest of the house in winter and hotter in summer.

For example:

40 feet long x 32 feet wide = 1,280 square feet

If it’s a two-story with that footprint, double the calculation to 2,560 square feet.

Likewise, if you have a finished basement the furnace will heat, add that space too.

Step 4 – Sun Exposure

If you play with data inputs the calculator a bit, you’ll notice that this factor can affect electric furnace size by up to about 5 kW, which would be about 17,000 BTUs, so that is significant. But think this through…

Shade – Winter vs Summer! This is a huge thing to remember. A home that is heavily shaded by hardwood trees in summer won’t be shaded as much in winter when the leaves are off the trees. So, consider winter shade when entering information on the electric furnace sizing calculator.

Tip: Also keep in mind that the sun is low in the sky, nearer the horizon in the winter months, so if there are hills or tall buildings to the South of your home, they might well create shading that lasts until mid-morning and begins again in mid-afternoon.

If in doubt, go with “Average” or “Heavily Shaded.”

Furnace Sizing Calculator Results

Once you have plugged in your information, the Calculator will show you several pieces of information.

1). Recommended furnace size in kW, or really kW/hour. It expresses how many kWs, or kilowatts, of heat the furnace should be able to produce each hour if it ran continuously.

A kW is 1,000 watts. If you have a 1,500-watt hair dryer, for example, it is 15 kW.

Electricity providers bill customers in kW/hours, so that’s a good unit to work with.

2). The equivalent BTUs. One watt equals 3.412 BTUs, so one kW equals about 3,400 BTU.

This BTU to kW Conversion Chart shows common electric furnace sizes in both units.

30,000 BTU9 kW
40,000 BTU12 kW
50,000 BTU15kW
60,000 BTU18 kW
80,000 BTU24 kW
100,000 BTU30 kW

Increments of 10,000 are used for the BTUs because gas and oil furnaces are typically manufactured in these increments. This makes comparison easy if you wanted to know the equivalent gas or oil furnace size to the recommended electric furnace size.

3). Recommended Wire Size

Larger wires carry more electricity, so sizing the wire is a significant factor in the process of choosing and installing an electric furnace.

4). Amp Circuit Breaker

Our Calculator shows how many amps are needed to handle the furnace of the size you need.

Note that individual circuits might not be large enough. In that case, the electrician will use two circuits to meet your electrical needs. This is common when installing an electric furnace of more than about 20 kilowatts.

Quick View – Recommended Electric Furnace Size at a Glance

This chart allows you to see the furnace size you need very quickly. Our readers also use it to verify the results they received from our electric furnace sizing calculator.

Room SizeElectric Furnace Size
for Hot Climate
(Zone 1&2)
Electric Furnace Size
for Warm Climate
(Zone 3)
Electric Furnace Size
for Moderate Climate
(Zone 4)
1,000 sq ft9 – 11 kW11 – 12 kW14 kW
1,200 sq ft11 – 13 kW13 – 15 kW16 kW
1,500 sq ft14 – 16 kW16 – 18 kW20 kW
1,600 sq ft15 – 17 kW17 – 19 kW22 kW
1,800 sq ft16 – 19 kW19 – 22 kW24 kW
2,000 sq ft18 – 21 kW21 – 24 kW27 kW
2,500 sq ft22 – 26 kW26 – 30 kW33 kW
3,000 sq ft27 – 31 kW31 – 36 kW40 kW

For example, with a 20 kW electric furnace, you can heat a 2,000 sq ft house in Zone 2. If you’re living in Zone 4, a 20 kW electric furnace would only heat a 1,500 sq ft home.

Electric Furnace Sizing FAQs

These common questions give more detailed information many homeowners and installers are looking for.

What is the 20kw electric furnace wire size? (or 20 kW electric furnace wire size?)

The most common setup for a 20 kW furnace is a 240-volt supply. This would require about 84 amps, and to meet that load requirement, you would need a 3 AWG copper wire (#3 wire or #3 AWG wire). This is for single-phase installation.

For 3-phase installation, there would be about 28 amps per phase. In this case, #10 wire, or 10 AWG wire, would be the minimum requirement.

What size breaker for 20 kw electric furnace with #6?

Stated with more detail, what size circuit breaker is needed for a 20 kW electric furnace wired with #6 wire, aka 6 AWG wire?

Here is a quick answer – but an electrician should make the final determination.

For single-phase installation, a minimum 100-amp breaker is needed to support 20 kW.

In 3-phase service, a 33 amp breaker is sufficient.

Again – Always consult an electrician! Our answers are generally accurate for most situations. However, every home, electric furnace and electrical requirements are different.

What size electric furnaces are available?

Most manufacturers make electric furnaces from about 5 kW to 20 kW. This is the equivalent of 17,000 to 68,000 BTUs.

However, a few brands make larger-capacity electric furnaces up to 30 to 40 kW, equal to about 100,000 to 135,000 BTUs.

Your calculator says I need a 44 kW electric furnace. What is the solution?

You will probably have to install two furnaces for separate zones or floors of your home. A good fit would be one 20 kW furnace and a second 24 kW furnace.

Another option, of course, would be to use a gas furnace instead. For the equivalent of 44 kW, you would need a 150,000 BTU furnace. While that is quite large, a few manufacturers make them that size.

One electric furnace or two?

If your home needs one of the largest electric furnaces available, more than 30 kW for example, you have the option of using one or two furnaces, each with separate ductwork and thermostat.

Two furnaces will cost more, of course, for the equipment and installation.

However, having two furnaces might help you reduce electricity costs in the 15-20 years the furnaces will last.

If you use all parts of your home equally through the day, then one large electric furnace is a better fit. However, if you use the bedroom wing at night and the rest of the house during the day, then having two furnaces with programmable thermostats will reduce energy use by up to 30%. Set the bedroom area to be warm at night and cool during the day. Do the opposite with the rest of the house that is used more during daytime hours.

Electric furnace vs gas furnace – which is cheaper?

The electric furnace will cost less to buy and install. They’re cheaper to make, and no venting is required, so the labor and materials costs for installation are lower.

A natural gas furnace will cost much less to operate. Yes, we know that electric furnaces are “100% efficient” and that the gas furnaces you’re considering in a warm climate are probably 80% efficient – maybe 90%.

However, electricity costs much more than natural gas, so even if 10% or 20% of the gas heat is wasted/lost out the vent, the operating cost will still be lower. Comparing electric furnace efficiency to gas furnace efficiency is not an “apples to apples” comparison. You must compare how much the electricity will cost vs how much the natural gas will cost.

Propane is more expensive than natural gas, so if your options are electric furnace vs propane furnace, the propane furnace will still cost less to operate, but the difference won’t be as great.

Electric vs gas furnace – Which costs less?

This is a similar question, but let’s look at it a different way.

Consider the 10-year cost. This includes the upfront cost of the furnace and installation plus the cost of energy/fuel for 10 years.

In Zones 1-3, you might be better off with an electric furnace, since you won’t need a lot of heating in most winters, so your electric bills will be moderate.

In colder parts of zone 3, and definitely in Zones 4 & 5, studies show that your 10-year costs will be lower with a gas furnace, especially a natural gas furnace. That’s our recommendation.

Electricity vs Natural Gas vs Propane

Washington State University has a highly regarded Heating System Cost Calculator covering all heating system types.

It allows you to see the costs of any heating system type and let’s you compare two different types – your current system vs a new system, for example.

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 and EPA & R-410A Certifications.

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