Free Manual J 7 load calculator. Built by Dave Hartzell, Master HVAC, Kingfisher OK.
I have been sizing systems in Central Oklahoma for 45 years. Most contractors guess at tonnage off square footage and end up with oversized AC that short-cycles, sweats ducts, and never really takes the humidity out. A real load calc takes the guesswork out. This tool runs the same Manual J 7 math I use on every Hartzell’s bid.
Plug in your rooms below. I will give you total heat loss, total heat gain, design CFM per room, branch duct sizes, and a recommended tonnage. If you want it stamped for a permit, an IGSHPA geothermal install, or an ENERGY STAR Homes packet, I run that on Cool Calc Pro or Wrightsoft Right-J. Call me at 405-375-4822 for a stamped report.
Need this run for you? Email me your floor plan and I will run it free. 4.8 stars / 276 reviews. Master HVAC license. NATE certified. IGSHPA accredited.
Project basics
Rooms
Add each conditioned room. Sqft is the floor area. Perimeter is exterior wall feet only.
Windows are total glass area in each direction.
Custom new construction, IGSHPA geothermal, ENERGY STAR Homes, and IECC code submittal require ACCA Manual J 8.
Call 405-375-4822 if you need a stamped MJ8 report.
Frequently asked questions
How much does a Manual J load calculation cost in Kingfisher Oklahoma?
Run the calculator on this page free. If you want me to verify the numbers in person before a replacement quote, the in-home estimate is free too. The $111 diagnostic fee only applies when I’m troubleshooting a broken system, not sizing a new one.
Why does Manual J sizing matter for my Oklahoma home?
Oklahoma summers run 100 degrees with humidity, and our winters drop below 20. An oversized AC short-cycles, never pulls humidity, and dies young. An undersized one runs nonstop on the hottest day. Manual J is the only honest way to size it right.
Can I use the load calc result to get a quote from Hartzell’s?
Yes. Save the PDF or screenshot the result and call me at 405-375-4822. I’ll cross-check it against your home in person, then build a quote on the right tonnage. No guessing, no rule-of-thumb.
How accurate is an online Manual J versus a full in-home calc?
This calculator gets you within roughly half a ton when your inputs are honest. For a final replacement bid I still walk the house, measure windows, check insulation, and run a full ACCA-grade calc. Free, no obligation.
Do you also size geothermal systems with Manual J?
Every geothermal install I do starts with a Manual J load, then a Manual S equipment match, then a loop sizing. I’ve been IGSHPA accredited since I started doing geo, and I won’t drill a single hole until those numbers line up.