Manual J Lite • Works instantly in your browser
Calculate the exact BTU load and correct furnace, AC, or heat pump size for any room or whole house — before a contractor quotes you.
Get Instant Access — $19Works instantly in your browser — no account needed
Oversized HVAC systems short-cycle, waste energy, and cost more upfront. Undersized systems can't keep up. This calculator gives you the numbers to have an informed conversation.
See the correct tonnage for your space so contractors can't upsell you a bigger, pricier system than you need.
Hand contractors a clean BTU and sizing breakdown so every quote is compared against the same numbers.
A properly sized system runs longer cycles, dehumidifies better, and keeps every room at an even temperature.
Square footage, insulation level, window count, climate zone, ceiling height, and occupancy.
The Manual J Lite engine estimates heating and cooling BTU load and recommends unit tonnage.
Download a clean, printable sizing report to bring to any HVAC contractor.
No spreadsheets, no guesswork, no waiting on a contractor to run the numbers.
Get Instant Access — $19Works instantly in your browser — no account needed
It's a simplified "Manual J Lite" estimate built for homeowners. It gives you a strong, informed ballpark for BTU load and unit sizing so you can sanity-check contractor quotes — not a stamped engineering document for permits.
No. It works instantly in your browser — no account, no downloads, no setup. Enter your details and get results immediately.
Yes. Calculate a single room, a zone, or the entire house. Each calculation produces its own printable report you can save or bring to a contractor.