15+ years • 6,500+ jobs completed • 1,500+ Oklahoma homes served
★ HAPPY 4TH OF JULY ★
July 4th in Oklahoma means a full house, a hot kitchen, and the AC running flat out. Before the cookout, let me make sure yours can keep up. I hold same-day spots open for no-cool calls across Kingfisher and Central Oklahoma, and new-system estimates are always free. $99 dispatch, $111 diagnostic on repairs. 4.8 stars, 290+ reviews. Happy Independence Day from my family to yours. Call 405-375-4822 or book at hartzellsheatair.com.
Straightforward pricing
- $99 dispatch on every truck roll. Free on new-install estimates.
- $111 diagnostic, part of the $210 flat repair-call price. Accept the estimate within 10 days and I give the $99 dispatch back.
- Free estimates on new installs. No charge to walk through replacement options.
Call (405) 375-4822. 4.8 stars / 290+ reviews.
HVAC Sizing EstimatorHow many tons does your Oklahoma home need?
The most common mistake I see is systems that are the wrong size. Oversized systems short-cycle and leave your house humid. Undersized systems run constantly and never keep up. I’ve been doing Manual J load calculations for 45 years, this estimator gives you a solid ballpark before we talk. Enter your details below.
Estimate Your System Size
I do a full Manual J load calculation on every install, no guessing. Free estimate, no pressure.
Get a Free Estimate from Dave
405-375-4822 | Free estimate on all new installs
This estimator uses Oklahoma climate zone data (Zone 3/4 mixed-humid) and Rule-of-Thumb sizing guidelines. Actual sizing requires a Manual J calculation accounting for your specific home’s envelope, ductwork, orientation, internal heat gains, and local design temperatures. Oversizing by more than 0.5 tons causes humidity problems and short cycling. Do not size by square footage alone.
HVAC Sizing in Oklahoma: What You Need to Know
Oklahoma sits in Climate Zone 3/4, mixed-humid, with brutal summers (design temperature 99°F in Kingfisher) and cold enough winters that you need real heating capacity. The rule of thumb is 400, 500 BTU per square foot for cooling, but that changes dramatically based on your home’s envelope. I have seen two identical-square-footage homes in the same neighborhood need systems half a ton apart because of insulation and window differences.
The industry standard sizing method is Manual J. It accounts for your home’s exact dimensions, ceiling heights, insulation values, window U-factors, orientation, internal heat gains (appliances, people, lighting), ductwork efficiency, and local design temperatures. I run Manual J on every install because guessing wastes your money one way or another.
What happens if my HVAC system is oversized?
An oversized system short-cycles, it cools or heats too fast, shuts off, and never runs long enough to remove humidity. In Oklahoma’s humid summers, this leaves your house cold but clammy. Short-cycling also wears out the compressor faster. Most contractors oversize because a bigger unit makes customers feel confident. The right size is the one that runs the longest cycles at design conditions.
What happens if my system is undersized?
It runs constantly and cannot maintain temperature on the hottest or coldest days. Your energy bills are high, the equipment wears out faster, and you are uncomfortable. On a 100°F Oklahoma day, an undersized system will fall behind by noon and never recover.
Is the rule of 400 sq ft per ton accurate?
It is a starting point, not a finish line. In a new well-insulated Oklahoma home, you might need 450-500 sq ft per ton. In a 1960s frame house with no insulation, maybe 250-300 sq ft per ton. Ceiling height, window area, and sun exposure matter just as much as square footage. The rule is useful for a ballpark conversation, not for ordering equipment.
How do I know what size system I have now?
Look at the model number on your outdoor unit. Most manufacturers encode the nominal capacity in the model number. Common codes: 018=1.5 ton, 024=2 ton, 030=2.5 ton, 036=3 ton, 042=3.5 ton, 048=4 ton, 060=5 ton. The number is BTU/hr divided by 1,000. Divide by 12 to get tons. If you cannot find it, call me and I can usually identify it from the model number over the phone.
Should I oversize my system to be safe?
No. This is the single most common mistake contractors make, and most of them know better. Oversizing does not give you a buffer. It gives you a humidity problem and a shorter equipment life. Proper sizing for Oklahoma means your system should struggle slightly on the absolute hottest 1% of days. That is how Manual J works. If it always keeps up easily, it is probably too big.
Does geothermal use the same sizing rules?
Same Manual J process, but geothermal systems are sized differently because they handle both heating and cooling efficiently. The loop field is also sized to match the system. I run a complete ground loop design alongside the Manual J for every geothermal install. This is part of what IGSHPA accreditation covers.
Free Manual J Sizing, Every Install
I do not guess. Every new system I install gets a full Manual J load calculation. I tell you exactly what size you need and why. No upselling a bigger unit. No guessing and hoping.
Call Dave: 405-375-4822
4.8 stars / 290+ reviews | IGSHPA Accredited | 45 years experience | BBB A+