About HowManyBTUs.com
HowManyBTUs.com is a free, privacy-first calculator site designed to help you estimate heating and cooling needs for rooms and homes.
Last updated: 2026-02-25
On this page: What this site is · What it isn’t · Our calculators · How it works · Privacy · Affiliate disclosure · FAQ
What this site is
Sizing HVAC equipment can be confusing. People often ask: “How many BTUs do I need for this room?” or “What tonnage AC should I buy?”
HowManyBTUs.com provides easy calculators that estimate BTU/hr needs using common, practical sizing inputs: room dimensions, ceiling height, insulation quality, windows, sun exposure, occupants, duct condition, and more.
The goal: help you get into the right ballpark quickly so you can compare equipment options, understand contractor recommendations, and avoid obvious under- or over-sizing.
What these calculators are (and aren’t)
The results are planning estimates — great for room-by-room sizing, quick comparisons, and understanding what “looks reasonable.”
However, this site does not replace professional HVAC design. Whole-home sizing and equipment selection can require detailed load calculations (ACCA Manual J) and matching equipment performance data (Manual S), plus duct design (Manual D) when applicable.
Safety reminder: HVAC work can involve electricity, gas, refrigerant, ladders/attics, and permits. Always follow manufacturer instructions and local codes.
Our calculators
HowManyBTUs.com includes 13 calculators and guides covering cooling, heating, efficiency, and comfort:
Cooling & heating sizing
- BTU Calculator (quick) — fast estimate by room size
- Advanced BTU Calculator — detailed load with climate zone, insulation, windows, ducts
- AC Size Calculator — BTUs to tons for central AC
- Mini Split Calculator — single and multi-zone ductless sizing
- Window AC Calculator — room-by-room window unit BTUs
- Portable AC Calculator — SACC-adjusted portable AC sizing
- Heat Pump Calculator — year-round heating + cooling sizing
- Furnace Size Calculator — BTU output by square footage and climate
- Space Heater Calculator — wattage and BTUs for supplemental heating
Comfort, efficiency & costs
- Dehumidifier Calculator — pint capacity by room size and dampness
- SEER Savings Calculator — compare efficiency ratings and payback
- Energy Cost Calculator — monthly HVAC operating cost by fuel type
- Ceiling Fan Calculator — blade span, CFM, and downrod by room
- Air Filter Size Calculator — filter dimensions, MERV, and replacement schedule
Equipment & shopping
- Heating & Cooling Equipment by BTU Range — browse ACs, mini splits, heat pumps, heaters, fans, and filters
Some calculators have region-specific versions for Texas, Florida, California, Canada, and Ontario — pre-set with sensible climate zone and insulation defaults for each area.
How it works (in plain English)
At a high level, the calculator starts with a baseline BTU/hr estimate from the size of the space, then adjusts for real-world factors like ceiling height, insulation quality, windows and sun exposure, number of occupants, and duct losses.
These adjustments are designed to reflect how homes actually feel in summer and winter — especially in hot/humid regions where humidity and attic ductwork can change the “real” cooling load.
All calculations run locally in your browser using JavaScript. No data is sent to a server.
If you need code-compliant sizing for a full system, a Manual J calculation is the right next step.
Privacy-first by default
Calculator inputs are processed locally in your browser. The values you enter are not stored and are not transmitted to our servers as part of normal use.
We use Google Analytics in a privacy-friendly configuration (IP anonymization, no ad signals, no personalization, consent defaults to denied) to understand general usage patterns. See our Privacy Policy for details.
Affiliate disclosure
HowManyBTUs.com is a free resource supported in part by affiliate commissions. If you click a product link and make a purchase, we may earn a small commission at no extra cost to you.
We aim to link to products that are relevant to the calculator or topic being viewed. You are never required to purchase anything through our links.
See Affiliate Disclosure for more details.
Frequently asked questions
Are these BTU calculators accurate?
They’re designed to be accurate for planning and typical use cases. Results are estimates based on your inputs and sizing heuristics. For whole-home sizing and final equipment selection, a professional Manual J calculation is recommended.
Do you store the data I enter?
No. Calculations run entirely in your browser. The values you enter are not stored or transmitted to our servers.
Do I need to create an account?
No. All calculators are free to use and do not require registration.
Why do region pages exist (e.g., Florida, Texas, Canada)?
Region pages pre-set sensible defaults (like climate zone, insulation quality, and preferred units) to make the calculator faster to use. You can still adjust all inputs for your specific home.
How is this site funded?
HowManyBTUs.com is supported by affiliate commissions. When you click a product link and make a purchase, we may earn a small commission at no extra cost to you. Product links are always relevant to the calculator or topic, and you are never required to purchase anything. See the affiliate disclosure for details.
Questions or feedback?
If you found an error, have a suggestion, or want to report a broken link, please contact us. See the full sitemap to browse all pages.