This HVAC Heat Load Calculator will help you estimate proper system size in BTUs/h, base on simplified Manual-J method, that accounts for your home size, heat loss, geographic/regional adjustments, etc., to give you a pretty accurate size of you cooling/heating system, tailored to your home, as well as Estimated Cost of new HVAC system.

Calculate Your Heat Load (BTUs) in OH

Do you know what size Central AC or Heating System (furnace or boiler) you need? HVAC contractors are often lazy, and don’t do required Manual-J heat load calculation to properly size your HVAC system. Instead they oversize by 10-20%, to cover their “bases”. As a result, you as a customer overpay 10-20% in upfront costs. But that’s not the whole story.

Oversized HVAC systems also work not as designed – instead of running longer at 60-90% capacity most of the time, they run in short burst which use much more energy overtime, costing you much more in electricity / gas / oil / propane, and provide uneven comfort – you have 5 minutes of comfort and then wait 15 minutes where air is too cold or too hot. Oversized AC systems also do not remove enough moisture – so you end up with cold, yet humid home.

* For home size, enter only “conditioned space” square footage. If your garage or basement is not heated or air conditioned, don’t include it in the home size.

Importance of properly entering your home information to get accurate Heat Load of your home, and proper HVAC system size

If you enter information inaccurately, the result will be off. Therefore, we recommend that you accurately measure your heated/conditioned living space & ceiling height, and select your home insulation levels, number of windows/doors, air-tightness of your doors/windows, shading/sun exposure of your home, etc.

Our BTU / Heat Load calculator uses less aggressive Heat Load BTUs per cubic foot, than a typical contractor would use, to avoid doing a time consuming Manual J heat loss calculation. Our values are more realistic, and are dynamically adjusted, based on your location and heat loss through doors / windows, walls and ceilings (attic).

How to properly enter your house information:

Note – most of the optional steps can be left as “default” values, unless they drastically differ from your actual home. Still we recommend that you review the optional setting, and change as needed.

STEP 1: Select your climate region, based on US Climate Region map at the top of the calculator. We use approximate geo-location to pinpoint your state. However some states can have as many as many as 3-4 different climate zones. So it is essential that you correct your region if it wasn’t detected properly. Refer to climate map of US to select proper region setting.

STEP 2: Select your HVAC system type. If you are looking primarily for Cooling heat load (BTUs) of your home, select “cooling only”. If only heating BTUs, select “heating only”. If both, select “heating & cooling”. This will be used for best HVAC system recommendation for you – both type of heating/cooling system, and size in BTUs based on Heating & Cooling BTUs requirements.

NOTE – for system recommendation, we also have two more inputs: Presence of Air Ducts (step #6) and/or Baseboards/Radiators (step #11). If you do or don’t have either of these, a central or ductless AC system will be recommended for Cooling and Heating, or a hydronic boiler system will be recommended as primary Heating system

STEP 3: Enter total square footage of heated/conditioned living space of your home. As mentioned above, only include area size the will be covered by your heating/cooling system. Including unconditioned living space will result in incorrect heat load calculation.

STEP 4: Enter number of rooms (zones) in your home. This value is used if you plan to zone your boiler or ductless heat pump, and will primarily affect estimated cost of recommended heating & cooling equipment.

Besides the cost, this is also an important input for adjusting total BTUs for heating and cooling, in case of using Ductless Mini-Split system or a boiler. Both of these systems have much smaller heat loss, as they don’t use Air Ducts, which have a typical heat loss (wasted energy) of about 25-40%, based on Energy.gov data.

Typical duct systems lose 25 to 40 percent of the heating or cooling energy put out by the central furnace, heat pump, or air conditioner – Energy.gov

Therefore, if you use a central air (ducted) system, your HVAC system size must be adjusted UP, to account for duct losses. At the same time, ductless and forced hot water radiators have a much smaller loss percentage (about 2-5%).

STEP 5: Select your home’s average ceiling height. This will have direct effect on home many BTUs of cooling and heating is needed. Most homes have 8 ft. ceilings, which is the default value.

STEP 6: Select if you have air ducts? If yes, and unless certain additional conditions are met, in most cases a Central Air heating & cooling system (equipment) will be recommended, and heat loss of of your home will be calculated based on additional waste in the ducts. Otherwise Ductless Mini Split will be suggested as cooling system, and boiled will be recommend for heating, except for Climate Region #5, where hydronic heating systems are not needed, and your heating need can easily be met by a Ductless or Central Heat Pump.

STEP 7: Choose your home insulation grade. In most cases, you will have 13R fiberglass/cellulose insulation inside 4″ stud wall. If you have 6″ stud insulated walls, you will likely have about 19R insulation. If you have 6″ walls with Closed Cell Spray Foam, you will have about 36R of insulating value (which is amazing).

On the opposite end, if you have older home, with 4″ walls, you will likely have no insulation. In this case, you can select “Less than Average” or “Poorly Insulated”, depending on how “leaky” or drafty your house is. This does not include leaky/drafty windows and doors, which have its own setting below.

STEP 8 (Optional): Select sun exposure of your home. This setting is optional, and can affect both heating and cooling, depending on the season. If you have mostly shaded home – in the winter, you will spend more on heat, and less on cooling in the summer. Reverse happens if you have very little or no shade – your house will be warmer in the winter and in the summer, as it will gain solar heat.

STEP 9 (Optional): Select number of windows in your home. Typical home has about 15 windows for every 1000 sq. ft. Select if you have more than average or less than average. This is important, as you loose/gain a lot of heat through windows (as much as 30% heat loss is through your windows, according to Energy.gov

STEP 10 (Optional): Select how air-tight or leaky/drafty your windows and doors are.
STEP 11 (Optional): Select if you have baseboards / forced-hot water radiators in your home. If yes, a boiler heating system will be “preferred” as heat system of choice in colder climates.

Calculating Your Home Heat Load, and understanding results:

Once you enter all the data (in most cases you will modify only 3-5 items), click calculate button. You will immediately see the results, which include:

• Estimated Heating BTUs
• Estimated Cooling BTUs
• Recommended Cooling System
• Recommended Heating System
• Approximate Cost to Install / Replace your HVAC equipment, as well as size in TONS & BTUs

Heat Load Estimates: As we mentioned above, we use simplified Manual J flow, to give you approximate Heat Load of your home, but instead of spending as much as 30 minutes on this calculation, it usually takes less than 30 seconds. As such, our results are not as precise as real Manual J calculation. Still we strive to be as accurate as possible, to provide a realistic and fairly accurate estimation.

As always – your “mileage” will vary, and we stress that these results are merely an estimate, and are provided for informational purposes only. You can use these results to keep your contractor “honest” and make sure you don’t get overcharged for to big of a system OR too small of a system is being proposed, which will not be able to meet your heating or cooling needs.

Cost Estimates: We use information from hundreds of HVAC contractors across US, as well as our own data on regional pricing adjustments, cost of labor, and most recent Heating/Cooling Equipment costs, to provide the most accurate fair market pricing in your state. However, each contractor prices their work differently and has different fixed costs, overhead, labor costs, etc. That’s why we provide three price ranges: Low End, Mid Range, and High End prices. In most cases, your actual price will be somewhere in the middle.

Does a higher price mean better quality? Not at all. Often, homeowners pick the high(er) bidder, and end up with terrible results. However, the lowest bidder, will most likely mean disaster, or at least poor quality. Rarely you will get great workmanship and bargain price. This is especially true in HVAC, where good service techs / installers are paid more, are high demand, and usually require a professional license, which takes years of experience and requires to pass state testing.

Therefore – if you get “too good” of a price from your contractor – either he is not that good, or he works “after work” and on weekends, and when you have problems, he won’t be available. I went through this 20 years ago, so I’m speaking from personal, very expensive experience!

Recommended Heating and Cooling Equipment: We use proprietary algorithm to recommend the best Heating and/or Cooling system for your home, which is picked based on heat load, geographic location, type of heat delivery method (ducts, radiators or ductless), as well as many other factors.

As each home, homeowner and situation is different, our recommendation may not meed your needs. However in most cases, our suggested equipment will be an almost perfect match. Same goes for size of your suggested HVAC system.

However, and this is very important: – you should not use these recommendations as primary source for choosing equipment type and size, as they are based on generic information! Have your contractor do an accurate heat loss estimate, specific to your home!

Next Step: Do more research and get quotes

First of all – the more you know, the better! You don’t have to become an HVAC expert (as I did, when I was picking my Ductless Heat Pump), but we recommend that you have at least a basic understanding of different heating and cooling systems available and used in US, to see and understand which is better for you. Otherwise you may end up with a very expensive purchase that does not work as you expected.

You can’t always rely on HVAC contractors – many are merely installers / estimators, and not all of them understand the equipment they install, follow up on latest technologies, or care enough to suggest what is best for you. First and foremost – you need to know what is best for you.

For example – many homeowners want to use Central Heat Pump for heating, but are unaware that these systems can only heat in outside temps ABOVE freezing. They they get an electric bill for $1000 and go like “what is this?” and “why so much?”. Had they done their basic research, and learn about technical limitations and dishonest marketing from HVAC manufacturers, they would never have picked such system.

When I was selecting a ductless heat pump with primary use as a Heating System in relatively cold Massachusetts, I spent more than a month researching and contacting tech support at different manufacturers, to learn and figure out what I needed.

You don’t need to spend so much time, as we have compiled a pretty substantial amount of guides that help answer most of our questions, as we went through these steps ourselves.