Manual J Load Calculation

What you get

• Room-by-room loadSensible and latent, heating and cooling, not one number for the whole space.
• Real design conditionsASHRAE 99% heating and 1% cooling for your actual ZIP, not a rule of thumb.
• Envelope by surfaceWall, glass, roof and floor taken separately with real U-values, plus infiltration.
• Equipment recommendationWhat capacity you need, and which units in that capacity actually fit your opening.
• Airflow and distributionCFM, and for high velocity the outlet count and where the runs can reasonably go.
• A document you can hand overTo your contractor, your board, or your filing engineer.

Common questions

What is Manual J, and why does it matter?

Manual J is the ACCA standard for calculating heating and cooling loads. It weighs more than thirty factors: every exterior surface with its own U-value, glass area and orientation, infiltration, internal gains, and the design temperatures for your specific location. The alternative is the rule of thumb, one ton per 400 to 600 square feet, which routinely oversizes equipment by half.

Why does oversizing matter? Surely bigger is safer.

It is the opposite. An oversized system short-cycles: it drives the temperature down fast, shuts off before it has removed any moisture, and leaves the room cold and clammy. It uses more energy doing it, and the compressor wears faster for the extra starts. In a humid climate like New York, correct sizing is what makes a room comfortable rather than just cold.

How is this different from the free estimator on your site?

The estimator on our sizing pages is genuinely useful and it is free, but it assumes a roughly square footprint and average window sizes, and it does not do per-window orientation or measured infiltration. It is built to narrow the options in thirty seconds. A Manual J is the real calculation, run in software, room by room, and it produces a document. Use the free one to get oriented and this one when you are committing money.

Do I get the fee back?

Yes. The $250 comes off your equipment order in full. If you order from us, the calculation effectively cost nothing. If you do not, you still keep the report and can take it anywhere.

How long does it take?

Two to three business days once we have what we need. If a floor plan is missing or the wall opening has not been measured, that is usually what holds it up, so send those with the request.

Do I need one for a straight like-for-like replacement?

Often not. If you are swapping a unit that has worked well for years in the same space, matching what is there is usually sound and we can confirm that on the phone for nothing. A Manual J earns its keep when the space has changed, when the old unit never really performed, when you are converting to a different system type, or when a board or a filing engineer wants to see the numbers.