Free to download. iPhone only.
HVAC Load Calculator
This HVAC load calculator gives you heating, cooling and the size in tons as soon as you pick a house size and a place. Think of it as an HVAC calculator for the truck: it runs on your phone, so it works in an attic with no signal.
What you get
The answer comes first
Type the size of the house and pick a place. Heating, cooling and tons show up at once, and stay in view while you type.
See where the heat comes from
Walls, windows, sun, air leaks and ducts, each with its share. A what-if list shows what to fix first. Then split the load by room and size every duct.
Check that the unit fits
Enter the size you plan to use and see if it fits the load. For a heat pump, see the balance point and the backup heat.
Hand over a clean PDF
Make a two page report with your logo and your client's details. It is made on your phone.
Cooling check
Cooling should cover 90 to 115 percent of the load. A variable speed unit can go to 130 percent. A furnace should give 100 to 140 percent.
The house needs 22,797 BTU/h. Green is the range that fits: 20,517 to 26,217 BTU/h.
Heat pump balance point
A 2 ton heat pump on this sample house.
Below about 28 F outside the heat pump cannot keep up alone. At 23 F the backup heat must add 4,054 BTU/h (1.2 kW).
Size the whole job from one screen
From the first number to the last duct, in the order you work on a house.
Heating and cooling load for the whole house
Pick the house size, the ZIP code and the year it was built. The app follows the sun on every side of the house, hour by hour, and finds the hottest hour. It follows the same steps as a Manual J load calculation. The result is an estimate in the style of ACCA Manual J, not a certified design.
It is an HVAC load calculation app for houses of any size, and a heat loss calculator for the coldest night of the year.
How many BTUs does a house need?
Skip the BTU per square foot guess. Enter the house and get heating and cooling BTU/h that match the sun, the walls and the air leaks. Use it as a BTU calculator for a whole house, or as an AC BTU calculator when only cooling matters. Tons come with every answer.
Pick the right AC, furnace or heat pump
Enter the unit you plan to use and see if it fits the load. On the cooling side it works as an AC tonnage calculator and an HVAC sizing calculator. For gas heat it is a furnace size calculator with the output range and the input size to look for. For a heat pump it is a heat pump sizing calculator with the balance point and the backup heat in kW.
Mini splits, ducts and airflow
Add each room and get its BTU/h, its airflow and a head size. That makes it a mini split sizing calculator for the whole house. Then the built-in ductulator, also called a duct calculator, turns CFM into a round or rectangular duct size. It is a quick CFM calculator too.
Free tools you can use right now
Each tool runs in your browser with the same engine as the app. Nothing to sign up for.
Questions people ask
Is the app free?
It is free to download. It has a free trial, then a subscription that Apple bills. The App Store shows the price and the trial length before you buy. You can cancel in the Settings of your iPhone.
Do I need an account or a signal?
No account. The math runs on your phone, so it works with no signal in an attic or a crawl space. You need a connection to start the trial or to restore a purchase.
Where are my jobs kept?
On your phone. Jobs, client details, company details and your logo are not sent to us. You can erase them in Settings. The privacy policy has the full list.
How exact are the numbers?
They are estimates in the style of ACCA Manual J. They are good for a first size and a second opinion. They do not replace a certified room by room design. Check your local code for what it asks for.
Is this a Manual J calculator?
It is an estimate in the style of ACCA Manual J. It uses the same kind of steps for walls, windows, sun, air leaks and ducts, and it is good for a first size and a second opinion. A full Manual J calculation measures each room on its own, and some permits ask for one. The app is not affiliated with ACCA.
How many BTU do I need for my house?
It depends on the size, the climate, the insulation, the windows and the air leaks, not only on the square feet. Enter them in the app and you get heating and cooling BTU/h for your house, and the size in tons.
What size mini split do I need?
Add each room with its size, windows and the way it faces. The app gives the BTU/h for each room and the standard head size to pick, so it works as a mini split BTU calculator. The Rooms screen adds up the total for the outdoor unit.
What size furnace do I need?
The furnace output should be 100 to 140 percent of the heating load. Enter the house, then the furnace input and its AFUE, and the app tells you if it fits.
What is not in the app yet?
There is no iCloud sync, no LiDAR room scan and no metric or Canada version yet. It is for iPhone only. There is no Android app.
Get your first number in a minute
Download the app and size your next job on the spot.
- Heating, cooling and tons
- Room by room with duct sizes
- A clean PDF with your logo
An estimate in the style of ACCA Manual J. It does not replace a certified room by room design. Manual J is a trademark of ACCA. HVAC Load is not affiliated with ACCA. Read the plain guide to the method.