HVAC Load Calc: Manual J

Estimate a home's heating and cooling loads with a simplified whole-house block calculation, see where the load comes from, and check the equipment you are quoting against it. Use the results as an initial estimate. If your project requires a certified room-by-room Manual J, you'll need a separate calculation.

New subscribers start with a free trial. After it, HVAC Load Calc requires a subscription for all the features below.

Enter the house details
- Floor area, ceiling height, and stories
- Use the site's ZIP code to find the nearest US weather station. You can also search by town, state name, or state code, or enter your own design temperatures.
- Indoor design temperatures, 70 °F heating and 75 °F cooling unless you change them
- Insulation presets for walls, ceiling, and floor, or your own U-values
- Can't see the insulation? Fill in typical walls, ceiling, windows, and air leakage from the year the house was built.
- Window area on each side, a glazing type or the U-factor and SHGC from the NFRC label, and how much of the east, south, and west glass is shaded
- Air tightness as a preset or a blower door CFM50 result
- Ducts in the attic, crawlspace, basement, or garage, with their insulation and sealing
- Occupants

See the results
- Design heating load (BTU/h)
- Design cooling load, split into sensible and latent loads (BTU/h)
- Equivalent cooling tonnage, with a plausibility check for unusually high or low loads
- The load by component: walls, ceiling, floor, doors, windows, sun, infiltration, people, and ducts

Check before you quote
- Equipment check: enter a unit's cooling capacity, heat pump capacities at 47, 17, and 5 °F, or furnace output. See the share of the load it covers, the ACCA Manual S range, the heat pump balance point, and the backup heat needed at design.
- Fuel use check: enter last year's gas, oil, or propane use and compare the load it implies with the calculation.

Save the job
- Start a new job, save changes to the current job, or save an independent copy
- Pick up an unfinished calculation after closing the app
- See each job's loads and tonnage in the saved list without opening it
- Saved jobs, your company details, and your logo sync through iCloud to your iPhone and iPad signed in to the same Apple Account. There's no separate sign-up.

Share a report
- Page one: the design loads, equivalent tonnage, and your equipment and fuel checks
- Page two: the design conditions and where they came from, the load by component, and every input
- Add the client's name, property address, notes, your company contacts, and your logo
- Review the PDF before sharing it like any other file

On iPad, the form and report sit side by side and update as you work.

How the calculation works
The calculation uses textbook ASHRAE heat transfer: envelope conduction, infiltration, solar and internal gains. ACCA Manual J block loads use the same basis. Duct losses follow the ASHRAE residential load factor method, and a blower door result is converted the way Manual J converts it. Design temperatures come from ASHRAE tables where available and from fifteen years of hourly NOAA records elsewhere.

The estimate assumes a square footprint and 40 ft² of exterior doors. You can't change those assumptions.

Cancel anytime in Settings.

Engineering reference only. This is a whole-house block load, not a substitute for a certified room-by-room Manual J or professional engineering judgment.

Terms: https://manualj.vovaluka.com/terms
Privacy: https://manualj.vovaluka.com/privacy