What Size Furnace Do I Need for a 2000 Square Foot House?

That’s a great question, and it requires answers to a few more questions before we can provide an accurate answer.

1. What’s your climate?  Find a map online that divides the country up into 5 climate zones.  If you can’t find one, here’s a quick sketch from warmest to coldest.

Zone 1: The Gulf coast states including TX, and the desert regions of AZ and CA.

Zone 2: The mid-south (KY, TN, northern AL & GA, the Carolinas.

Zone 3: The southern Ohio Valley and Mid-Atlantic states, southern parts of the lower Plains states.

Zone 4: The northern Ohio Valley Mid-Atlantic states, northern NE, IA and CO, and the Pacific Northwest.

Zone 5: The northern Rocky Mountain, Plains and Great Lakes states, New England

2. What’s a Btu?

This abbreviation stands for British Thermal Units and is a measurement of heat that furnace manufacturers use to specify how much heat their furnaces can create per hour.  Now, here are the number of Btu’s per square foot that you will need in each zone to effectively keep your home warm and toasty.

Zone 1: 35 Btu’s per square foot; Zone 2: 40 Btu’s per square foot; Zone 3: 45 Btu’s per square foot; Zone 4: 50 Btu’s per square foot; Zone 5: 60 Btu’s per square foot.  Stay with this, we’re almost there!

3.  Can you do some math?

Multiply the square footage of your home by the Btu’s you need per square foot and you are one step away from knowing what size furnace you will need to heat a 2000 square foot home.  Your math will look like this example: If you live in Zone 1, the warmest, your equation would be 2000 (sq. ft) x 35 (Btu per square foot) =70,000 Btu’s needed to heat your home.  You would need a furnace that can deliver 70,000 Btu’s per hour (but that’s NOT your final answer.  Read on!)

Zone 1: 70,000 Btu

Zone 2: 80,000 Btu

Zone 3: 90,000 Btu

Zone 4: 100,000 Btu

Zone 5: 120,000 Btu

4. How efficient is the furnace you plan to install?

No furnace is 100% efficient.  In other words, no furnace uses every Btu it creates to heat your home.  An 80% efficient furnace uses 80% of the Btu’s it produces to heat your home and loses 20% through exhaust.  A 90% efficient furnace uses 90% of the Btu’s it produces to heat your home.

Furnaces come in a range of efficiencies.  Standard is 80%.  Then there is a jump to 90%.  From there, it can be any number, up to about 97% which is the current maximum on the market.

This is where a second equation comes in.  Multiply the efficiency of the furnace you plan to use by its capacity, and that will determine how many usable Btu’s it produces.  For example, a 100,000 Btu furnace with 95% efficiency (100,000 x 95%) will provide 95,000 usable Btu’s per hour.  So, applying this math to your 2,000 square foot home, let’s look at some examples.

If you live in zone 1, you need 70,000 Btu’s in your 2000 square foot home to keep it comfortably warm.  A 90,000 Btu furnace that is 80% efficient (90,000 x 80%) will produce 72,000 Btu’s of usable heat per hour, almost exactly what you need.  We’ll use 3 common efficiencies, 80%, 90% and 95%, to show you what size furnace you’ll need for each of these efficiency levels in your zone.  We’ll round off the size of the furnace you need to the nearest 5,000 Btu’s since they tend to come in increments of 5,000 or 10,000 Btu’s. Remember, we are multiplying the Btu’s the furnace makes by the efficiency it offers, to find the number of usable Btu’s you need for your 2000 square foot home.

Zone 1: (70,000 Btu’s needed) 80% Efficient furnace:  90,000 Btu capacity; 90% Efficient: 80,000 Btu capacity; 95% Efficient: 75,000 Btu capacity.

Zone 2: (80,000 Btu’s needed) 80% Efficient furnace: 100,000 Btu capacity; 90% Efficient:  90,000 Btu capacity; 95% Efficient: 85,000 Btu capacity.

Zone 3: (90,000 Btu’s needed) 80% Efficient furnace: 115,000 Btu capacity; 90% Efficient: 100,000 Btu capacity; 95% Efficient, 95,000 Btu capacity.

Zone 4: (100,000 Btu’s needed) 80% Efficient furnace: 125,000 Btu capacity; 90% Efficient: 110,000 Btu capacity; 95% Efficient: 105,000 Btu capacity.

Zone 5: (120,000 Btu’s needed) 80% Efficient furnace: 150,000 Btu capacity; 90% Efficient: 135,000 Btu capacity; 95% Efficient: 125,000 Btu capacity.

The numbers above will give you a very close estimate of the size furnace you will need for a 2000 square foot house where you live.  The only way to get a more precise figure is to have a professional HVAC technician do a Manual J load calculation, which is a detailed analysis of your home.  These figures are a very close estimate, and should prove useful in your search for the right furnace.

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6 Comments

  1. Posted September 21, 2011 at 1:37 am | Permalink

    Hi I have a 15 year old gas furnace Janco/Goodman
    100,000btu input 80,000 btu output square footage is approx 1600 of house. according to all the info I read this furnace should be adequate. It is not, our bedroom is above our garage we freeze in the winter, the heat is forced hot air, the garage is insulated.
    Any recommendations for me.

  2. admin
    Posted October 7, 2011 at 7:52 pm | Permalink

    A bedroom above a garage is always going to be a problem. No matter how well you insulate the garage, the garage door itself will let in a ton of cold and you are going to feel the effects in your bedroom. I would look at supplementing the furnace with a localized heater (like a small electric heater). No matter how big of a furnace you have you will run into this problem. Either that or the remainder of the house will be way too hot.

  3. Rob't
    Posted October 28, 2011 at 12:44 am | Permalink

    Maybe a two-zone heating system, with one zone for your bedroom and the other zone for everything else?

  4. mr martin
    Posted November 16, 2011 at 1:37 am | Permalink

    i have a 75000 btu for 1000 sq ft it don’t seen to work until i put is on 76 on the thermostat

  5. mr martin
    Posted November 16, 2011 at 1:40 am | Permalink

    i have a 75000 btu force air gas furnace for 1000 sq ft home in phila. pa. it don’t seen to work until i put is on 76 on the thermostat

  6. admin
    Posted November 23, 2011 at 4:14 pm | Permalink

    If it works when the thermostat is turned up it would appear that the themostat is working properly. And if the furnace works once turned up to 76 it would appear that the furnace can function properly.

    Can you elaborate on other conditions? How warm is the house?