HVAC Load Calculator

Find out how many BTUs of heating and cooling your home or small commercial space actually needs, and what equipment tonnage to look for, with an HVAC load calculator that goes further than a flat square-footage rule of thumb. Enter your ZIP code to auto-detect your climate zone, describe your building's envelope and openings, and get separate heating and cooling numbers — plus a line-by-line breakdown of exactly what drove your result, so you can see why the number is what it is, not just what it is.

Choose Residential or Light Commercial, enter your ZIP code and building details, then calculate. Cooling load accounts for occupants, sunlight, and equipment heat since those all add warmth in summer; heating load leaves those out, since proper heating design sizes for the coldest morning with nobody home and nothing running. Formula: Cooling = Envelope + Windows + Doors + Occupants + Room/Appliance Loads · Heating = Envelope + Windows + Doors.

Building Type

Light Commercial uses higher occupancy and equipment-load assumptions than Residential. Large or complex commercial buildings need a licensed engineer's Manual N/ASHRAE assessment — see the FAQ below.

Location & Climate Zone

Enter your ZIP code to auto-detect your climate zone, then verify it — this is a broad regional approximation, not a precise map. See the FAQ if your ZIP doesn't resolve.

ZIP Code

Climate Zone — verify / adjust

Building Basics

Square Footage — conditioned area

Ceiling Height — feet

Envelope

Not sure what a field means? Tap the ⓘ next to its label.

Insulation Quality

Sun Exposure

Air-Tightness

Windows & Doors

Windows — count

Window Type

Exterior Doors — count

Occupancy & Heat Sources

Occupants

Equipment Heat — watts, optional

Kitchen Present?

Sunroom / Glassed Room?

Your Results

Cooling Load

—

BTU/h

Recommended Size

—

tons (cooling)

Heating Load

—

BTU/h

Climate Zone

—

used in this result

Formula: —

Cooling Load Breakdown

Results are for reference and estimation only. See full disclaimer below.

How to Use the HVAC Load Calculator

Choose Residential or Light Commercial

Pick the scope that matches your building — the calculator adjusts occupancy assumptions accordingly.

Enter Your ZIP Code and Building Basics

Enter your ZIP code to auto-detect your climate zone, then add square footage and ceiling height.

Describe the Envelope and Openings

Select insulation quality, sun exposure, and air-tightness, then enter window count and type, exterior doors, and occupants. Residential users can flag a kitchen or sunroom.

Review Your Results

Click Calculate to see cooling load, heating load, and recommended equipment tonnage, plus a line-by-line breakdown of what drove the number. Use Print to capture the results as they appear on screen.

Frequently Asked Questions

Is this the same as a Manual J calculation?

Why does the calculator show separate heating and cooling numbers?

What if my ZIP code doesn't match a climate zone automatically?

Can I use this for a commercial building?

How accurate is this compared to a professional load calculation?