Estimate your heating and cooling load
This is a rule-of-thumb estimate for planning, not a Manual J load calculation. It does not see your ductwork, ceiling height, window type or air leakage.
How the estimate works
A heating and cooling load is the amount of heat your home gains or loses on the worst days of the year. Equipment is sized to meet that load. The calculator starts with the size of your living space, multiplies by a typical figure for your climate zone, then adjusts for the things that most change the answer: how many windows the house has, how much sun it gets, and how old or well insulated it is.
Heating is measured in BTUs per hour, the same unit printed on a furnace label. Cooling is also measured in BTUs per hour, and air conditioners are commonly described in tons, where one ton is 12,000 BTUs per hour. The calculator shows both, so you can compare the number against what is already in your house or what you have been quoted.
- Living space: the heated and cooled area, not the garage or an unfinished basement
- Windows: more glass means more heat gained in summer and lost in winter
- Sun exposure: a house in full sun needs more cooling than one shaded by trees
- Age and insulation: older homes leak more, newer homes hold temperature better
- Climate zone: colder zones weigh heating more, hotter zones weigh cooling more
What the numbers mean
The heating result is the output your home needs. Furnaces are labeled by input, which is higher than output because no furnace turns all its fuel into heat. The calculator shows the input rating you would look at for a furnace around 80 percent efficient and one around 95 percent efficient. The efficiency of any specific model is printed on its label.
For cooling, the tonnage shown is rounded up to the nearest half ton. Air conditioners come in set sizes, so the practical question is which standard size is closest to your load, not whether the calculator is exact to the BTU. Treat every result as a range centered on the number shown.
Why a calculator cannot replace a site visit
A proper load calculation, often called a Manual J, looks at details a web form cannot see: the ceiling height, the type of windows, how well the ducts are sealed, how leaky the attic and walls are, and which rooms are above a garage or over a crawl space. Two houses of the same size can have loads that differ by a lot.
Use this tool to get oriented, to check that a quote is in a reasonable range or to decide whether to replace a system. Then have a technician look at the actual house before you commit. Rocket is happy to talk through your number by phone or text.
Sizing mistakes to avoid
Bigger is not better. An oversized air conditioner cools the house quickly, shuts off and never runs long enough to pull humidity out of the air, which leaves rooms feeling clammy. An oversized furnace cycles on and off often, which wears parts and wastes fuel.
Undersized equipment has the opposite problem: it runs constantly and still cannot keep up on the hottest or coldest days. Replacing a system with one just like the old one is also a risk, since the original may have been sized wrong, or the house may have changed since it was installed.
- Use the calculator to get a starting range.
- Compare it with the size of the equipment you have now.
- Ask a technician to measure and confirm before you buy.
- Ask how the size was chosen, not only what it costs.
Frequently asked questions
How accurate is this HVAC load calculator?
It is a planning estimate based on rules of thumb. A technician measuring your actual house will give a more reliable number than any web form.
What climate zone is Salt Lake City in?
Most of the Salt Lake Valley falls in zone 5 on the standard one-to-five scale used here, which weighs heating heavily. Select zone 5 for most valley homes.
How many tons of air conditioning does my house need?
The calculator shows an estimate from your inputs, rounded up to the nearest half ton. Confirm it with a technician before buying equipment.
Should I choose a bigger furnace or AC to be safe?
No. Oversized equipment cycles on and off too often, wears faster and does a poorer job of controlling humidity. Right-sized equipment runs longer and steadier.
Does this calculator give equipment prices?
No. It only estimates size. Call or text Rocket to discuss what your home needs.
