HVAC Load Calculator
Rough heating/cooling load.
Rough heating/cooling load.
How to use HVAC Load Calculator
- Enter floor area, ceiling height, and climate zone
- Set sun exposure, occupant count, and number of windows
- Read the estimated cooling BTU/hr and suggested AC tonnage
- Check the ballpark furnace size for heating
About HVAC Load Calculator
The HVAC Load Estimator gives you a quick, rough estimate of the heating and cooling capacity a room or home needs — no software to install and nothing to download. Enter your floor area, ceiling height, climate zone, sun exposure, number of occupants, and number of windows, and it returns an estimated cooling load in BTU/hr, a suggested air conditioner size in tons, and a ballpark furnace size for the heating side.
Because it sizes both sides, it works as a heat load calculator and a cooling load calculator in one place, and it shows how each input pushes the number up or down: warmer climate zones, taller ceilings, more sun, extra occupants, and more windows all raise the load. It is a simple, rule-of-thumb tool rather than a full Manual J load calculation, so treat the result as a starting point for planning a project or checking a contractor's quote, not a final equipment spec. Where paid packages such as ServiceTitan or Field Promax sell this as an app or a download, this one is a free web calculator you can open and use straight away.
It is completely free and runs entirely in your browser. Nothing you type is uploaded or stored anywhere, there are no sign-ups, and there are no limits — run as many estimates as you like while you compare room sizes, climates, or window counts.
It works as a quick HVAC load calculator — enter room size, climate and insulation to get an estimated heating/cooling BTU and tonnage.
Frequently asked questions
- Is the HVAC Load Estimator free to use?
- Yes, it is completely free with no sign-up, no account, and no usage limits. You can run as many estimates as you like.
- Do I need to download HVAC load calculator software or an app?
- No. This is a free web-based HVAC load calculator that runs in any browser, so there is nothing to install or download and no app to buy. It is a lightweight alternative to paid packages like ServiceTitan or Field Promax when you just want a fast estimate.
- Is my data uploaded or stored anywhere?
- No. Every calculation happens locally in your browser. None of the numbers you enter are sent to a server, saved, or shared, so your information stays private.
- Does it calculate the heating load too, or just cooling?
- It does both. Alongside the cooling load in BTU/hr and a suggested AC size in tons, it returns a ballpark furnace size, so it works as a heat load calculator as well as a cooling load calculator.
- Is this a Manual J load calculator?
- No. Manual J is the detailed, room-by-room ACCA standard that accounts for insulation, air sealing, ductwork, and local design temperatures. This tool is a quick rule-of-thumb estimate for planning; for final equipment sizing, have a professional run a full Manual J.
- Can I use it for a commercial HVAC load calculation?
- It is built around residential rules of thumb for a single room or a home, not commercial buildings. Commercial loads depend on things like occupancy density, equipment heat, ventilation codes, and lighting, so use a commercial HVAC load calculator or an engineer for those projects.
- How accurate is this HVAC load estimate?
- It is a rough rule-of-thumb estimate meant for quick planning and sanity-checking quotes. It does not account for insulation quality, air sealing, ductwork, humidity, or local design temperatures. For real equipment sizing, have an HVAC professional run a full Manual J load calculation.
- How do you convert BTU to AC tons?
- One ton of air conditioning equals 12,000 BTU per hour, so the tool divides the estimated cooling load in BTU/hr by 12,000. It then rounds up to the nearest half ton, since AC units are sold in standard sizes.
- How many BTU do I need per square foot?
- A common starting point is about 20 to 25 BTU/hr per square foot, which this tool adjusts up or down for climate zone, ceiling height, sun exposure, occupants, and windows. Warmer climates, taller ceilings, and sunnier rooms increase the load.
- Is there a simple, free HVAC load calculator I can use right now?
- Yes, this is one. It asks for only a handful of inputs, needs no download or account, and gives you a BTU load, AC tonnage, and furnace size in seconds. It is meant to be the quick, simple option before anyone runs the full numbers.
- Why shouldn't I just buy the biggest system I can?
- An oversized HVAC system short-cycles, turning on and off too quickly. That wastes energy, wears out the equipment, and does a poor job removing humidity. Right-sizing based on an accurate load calculation gives better comfort and efficiency.