HeatwaveReady

Find your cooler

Find your cooler: answer four questions and get the honest match. Or jump to a calculator: air conditioner BTU, evaporative cooler CFM, heat index. Every result names its rule and its source.

Some links pay us a commission, at no cost to you. How we earn.

What are you trying to do?

Pick the goal that sounds like yours. We’ll ask one or two plain questions, then show the size and the honest best-fit pick.

Sizes come from ENERGY STAR (air conditioners) and the US DOE (evaporative) — arithmetic on published values, nothing invented. We only point you to a unit that actually fits, and say so plainly when nothing we cover does.

Or go straight to a calculator

The same cited math that runs our guides: ENERGY STAR for air conditioners, the US DOE formula for evaporative coolers, the National Weather Service for heat index.

What size air conditioner?

Two questions; sized with ENERGY STAR’s table, then the unit here that fits.

Where this number comes from

A sizing guide built from ENERGY STAR’s published table, not a full Manual-J load calculation. For odd rooms (lots of glass, top floor, extreme climates) an HVAC pro’s load calc is worth it.

Evaporative cooler: how many CFM?

Room volume in, CFM out, by the US Department of Energy formula.

Where this number comes from

Formula, the 20–40 ACH range and the wet-bulb ≤70 °F effectiveness threshold are the US DOE Building America Solution Center (PNNL)’s own — validated against its Salt Lake City worked example (16,000 cu ft × 20 ACH ÷ 60 = 5,333 CFM).

Heat index & humidity check

Enter temperature and humidity: the feels-like heat index, the NWS level, and whether evaporative cooling helps.

Where this number comes from

Heat index uses the National Weather Service Rothfusz regression. Live readings come from api.weather.gov (US only, public domain) and stay in your browser — we don’t store your location. Not medical advice.

Why you can trust the answer

This isn’t a lead-capture quiz that funnels everyone to whatever pays us most. It’s arithmetic on published, official numbers, with the honest caveats built in:

  • Air conditioners are sized from ENERGY STAR’s own square-footage → BTU table (validated against the agency’s worked examples).
  • Evaporative coolers use the US Department of Energy’s formula — CFM = (room volume × air changes per hour) ÷ 60 — and we tell you up front that they only work in dry air.
  • Fans get no fake “size” — a fan doesn’t lower the temperature, it moves air so you feel cooler. We match your priority (quiet, smart, budget) to a fan whose real specs fit, and say so.

And when the honest best pick isn’t a brand we can earn a commission on, the tool says so to your face. The recommendation stands on merit, never on our payout.

Want the full breakdown?

The finder is the fast front door. Each tool has a deeper page with the complete, cited math and every honest caveat:

Questions people actually ask

How do I know what size air conditioner I need?
Match the room’s square footage to a cooling capacity in BTU. ENERGY STAR’s table starts at about 5,000 BTU for 100–150 sq ft and rises from there, with adjustments for very sunny or heavily shaded rooms, extra occupants and kitchens. The finder on this page does that math from your room size; the full calculator adds the sun, occupant, kitchen and ceiling-height rules.

What’s the difference between BTU and CFM?
BTU measures heat removed and is how refrigerant air conditioners (window, portable, mini-split) are rated. CFM measures airflow and is how evaporative coolers and fans are rated, because they move air rather than refrigerate it. You can’t convert one to the other — they describe different things. Use the “cool a room down” path for air conditioners and the “dry-climate cooler” path for evaporative coolers.

Will a fan cool my room down?
No — a fan doesn’t lower the air temperature. It moves air across your skin so you feel a few degrees cooler, which is great for sleeping and taking the edge off, but it’s not a fix for dangerous heat. If the air itself is dangerously hot, you need an air conditioner (or, in dry climates, an evaporative cooler), not just a fan.

What if nothing you recommend fits my space?
The finder will tell you. If your room is bigger than anything we cover can handle, it says so and suggests a higher-capacity unit, two units or central air. If your air is too humid for an evaporative cooler, it steers you to a real air conditioner instead. We’d rather send you elsewhere than sell you the wrong box.