HVAC Load Calculator – Estimate the Size of Your Heating / Cooling System (in BTUs)

This HVAC load calculator, is a simple yet accurate tool that provides accurate real world heat load estimate for both Heating & Cooling.

We use a proprietary BTU calculation algorithm, that DOES NOT over-specify the unit capacity. Most online tools give you a higher heat load estimate then you actually need for your home to sell you more expensive equipment.

Estimate HVAC system load now:

sq. ft.

Estimated Load Cooling: 0 BTU Heating: 0 BTU
Recommended Equipment Cooling: Heating:

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How to use the heat load calculator

It is important that you enter accurate/appropriate details into the calculator. This HVAC Calculator brings you as close to a complicated Manual J estimation as possible. Otherwise, you may end up with a system that is too big or too small.

We also recommend that IF you plan to use the results of this heat load calculation for making your purchasing decisions, you SHOULD verify the results with this long-form Manual J online estimator.

HVAC sizing guide

Getting the right size HVAC system for your home/building is essential to providing enough capacity to heat or cool your living space. If your Heating or Cooling system is too small, you won’t get enough BTUs, and the space won’t be comfortable.

If you get too big of a system, you will be overpaying for the extra capacity: Bigger system = higher cost of installation. You will also be paying too much in operating costs (be it gas, electric or oil) going forward.

Most residential HVAC/Plumbing contractors do not want to spend the time to properly calculate (using Manual J method) the heat load & heat loss of your house (or individual rooms). So instead to cover their “bases”, 99% of pros specify oversized systems (which as explained above, costs more to install and operate).

NOTE: Most contractors and equipment distributors use INFLATED BTU/h values when calculating the heat load and unit size (in tons/BTUs), primarily to cover their backs.

Our calculator uses lower BTU/h values for both Heating & Cooling, to provide a more a “real-world” heat load estimate. However, we strongly recommend that you (or your contractor) do a Manual J heat load calculation of your home or a specific area, before making any purchasing decisions!

This calculator should be used and is intended for Informational Purposes only!

How to calculate HVAC load

Step 1 (Climate Region): Select your Climate Region, using the Region Map at the top on the calculator. For example, if you live in NYC or NJ, select Region 3 (yellow). If you live TX, select Region 5 (red), etc.

Step 2 (Area Size): Enter square footage for your house/building or a specific area, for which you are doing the calculations.

This step is Critical for accurate estimation of annualized heating/cooling loads of your HVAC systems! If you leave all settings as default, and only change the Region from 1 to 5 and back, you will see a huge change in Cooling/Heating BTU load.

Step 3 (Rooms / Zones): Enter number of Rooms/Zones where you want a new Heating/Cooling system installed.

If you plan to use a Central AC + Air Furnace (ducted) system, or a central boiler for heating, the number of zones is not very important in terms of estimating heat load.

This value is most useful for figuring out which type of Ductless Mini-Split system to use.

Additionally, we discuss the PROS & CONS of using a multi-zone vs. installing multiple single-zone Ductless heat-pump systems, in our Mini Split DIY installation guide.

Step 4 (Space Height): Select average Ceiling Height of your house. In most cases this value should be equal to 8 ft. However if you have high ceilings, or cathedral/vaulted ceilings, the VOLUME of your space will be higher.

For cathedral/vaulted ceilings, add the lowest wall height + peak height, and divide by 2, to get the average. For example:

Your exterior wall is 8 ft. high, and the highest point on the ceiling is 12 ft. high. In that case, your average Ceiling Height is 10 ft:
(12 + 8) / 2 = 10

Step 5 (Insulation Grade): Most homes in US built between 1978 and 2000 will have 4″ studs with R-13 wall insulation, and should have R-38 roof / attic insulation. If this matches your home, leave this value as default (Avg. Insulation R-13 walls).

If you have a newer home with 6″ studs, will have R-18 insulation. In this case, select “More than Average” value.

In most cases you should not use “Very Well Insulated” value, unless you have a “Super-insulated” house.

If you have partially insulated home, select “Less than Average” or “Poorly Insulated”.

These two values are most critical in terms of heating, where your heat loss will be the highest. If your primary reason for installing a new HVAC system is cooling, we recommend using “Less than Average” value, to not over-size your cooling equipment.

Step 6 (Windows): Select the average amount of windows in your home. If you have ~1 window or fewer, for every 8 feet of exterior wall length, select “Average Amount”.

If you have more than 1 window, for every 8 feet of exterior wall length, select “More than Average”

Step 6 (Windows/Doors air tightness): Select appropriate window/door insulation level. In most cases, leave this as default “Average” value.

Understanding the results of HVAC load calculation

Unlike other online HVAC calculators, we provide estimated heat load (system size in BTU/h) for both Heating & Cooling as well as recommended HVAC equipment type and size!

You will get TWO results:

1) Cooling & Heating Load in BTUs – this is the actual calculated number of BTUs per hour & TONs needed to heat/cool your space.
2) Best matching Heating / Cooling equipment type for your needs.

1) Estimated Heat Load

You will get an approximate BTU / TONs load for your house, based on the information you entered in the calculator and your region. Both heating and cooling BTU results, are calculated using our optimized BTU calculation algorithm, which is more “conservative” than most HVAC contractors and equipment sellers will give you.

On average these values will be 20-30% lower than “contractor’s guestimate”. However we recommend that you use the lower numbers, for reasons discussed above.

2) HVAC Equipment Recommendation

Our calculator tries to provide the best match / recommendation for equipment to use your particular situation, based on your Climate Region and other inputs.

Equipment Recommendation needs further clarification, as each person’s situation is different. Ideally, this calculator would be perfect for a new construction home, where you have total control of design and specifications of the type of HVAC equipment that will be used. However, most homeowners in US are dealing with existing homes, which brings certain limitations.

First of all, if you have a Duct System in your home, a Central AC + Hot Air Furnace will be the most cost-efficient system for you.

If you don’t have air ducts, and/or cannot install ducts in your house, a hydronic boiler heating system will be ideal if you live in Regions 1 & 2, and a Ductless Heat Pump will be perfect for cooling.

In Regions 3, 4 & 5, you rarely have very cold weather. Therefore, a Ductless (mini-split) Heat Pump system can (and should) be used for both heating & cooling. Here is why:

Ductless heat pumps can both heat and cool your house, and they are pretty good at doing both. Since they can provide heating, and do so using a fairly low amount of electricity (3-4 times less than electric space heaters), you do not need to install an additional heating system, be it furnace or boiler, saving yourself about $7,000-12,000+ in installation costs.

Ductless systems are “modular” and operate on zone level. So if you are spending most of the day in the living room, there is no need to cool or heat the entire house! You only need to run 1 zone. At night, you can turn off the living room zone, and turn on the zones in bedroom(s).

Ductless systems are also about 2x more efficient than even the high efficiency modern Central AC systems, which means your electric bill will be 2x lower! Actually even more than 2x, because of zoning, which is nearly impossible to do with central air conditioning systems.

Which HVAC equipment to pick?

As mentioned above, if you live in northern climate regions, we recommend a Gas Boiler for heating and Ductless (mini-split) AC for cooling. If you already have ducts, it will be cheaper in the short term to go with Central AC + Hot Air Furnace.

However, in some cases you will get a Mini Split recommendation for both Cooling and Heating, but the BTU size will be different.

We know this part is confusing. So let’s look at it in depth:

Most Mini-Splits are rated based on their COOLING capacity. A 12000 BTU (1-TON) mini split will have a rated capacity close to 12000 BTU/h. However these same units can also HEAT! And most higher-end Mini Split units will have a much higher heating capacity!

Example: a 9000 BTU Fujitsu RLS3H (single zone) will has a 21000 BTU max-heating capacity! Therefore, if you live in zones 3,4 & 5, and plan to get a ductless system for your entire home, use the COOLING size when choosing the equipment. In most cases there will be more than enough heating BTUs available!

In Region 1 & 2, you need to take a closer look at specifications of your unit. However in most cases, in larger systems (2-8 multi-zone installations) the difference in Heating and Cooling BTUs is not as big as in the example above. Therefore, you will either have to oversize a little, or install multiple Single-Zone units throughout your home, to get highest efficiency and available capacity.

If you are unsure which type of heating or cooling system to install in your house, get 3-4 free estimates from local HVAC pros.

Cold climate mini splits: do they heat well?

Many homeowners looking to add an efficient heating system that can be used during the cold months of the year are very skeptical about installing a mini split heat pump. After all, they are primarily used for cooling purposes. However, the reality is that if you get a mini split heat pump DESIGNED for cold weather, it will heat your space in a way that will surprise you – you will be very warm and happy!

Instead of listing all the pros & cons, and potential scenarios, I will give an example. Five years ago, New Brook elementary school in Newfane, Vermont installed Ductless heat pumps + solar panels for HEATING and cooling of the building, with a backup propane boiler (only for days with temps below -4F). This was an unprecedented choice of heating for a school building in this area, and many people were against it. However, the upgrade was finally approved and is working very efficiently to this day.

This means that heat pumps can produce enough heat in cold climates, AND be cost efficient! Pair that with roof-top Solar, and you will have free heating in 5-8 years.

However, if your power goes down, you may be left without heat! Therefore it is important to have a backup plan, if you live in northern climates and want to use mini-split heat pumps for heating!

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