HVAC System Sizing Oklahoma: How I Size a System

The most common mistake I see is a system that is the wrong size. An oversized system short-cycles and leaves your house humid. An undersized one runs constantly and never keeps up. I have been in this trade 47 years, and sizing is something I do in your home with a heat load calculation, not on a web form. Enter your details below and I will show you what I check and how to get a free in-home sizing check.

How do I size an HVAC system for an Oklahoma home?

I size a system with a heat load calculation, and I run one before I size any system. For a home that is an ACCA Manual J, worked room by room, which adds up how much heat the house gains in summer and loses in winter.

The equipment gets matched to that load, not to the old unit or the floor area. ACCA describes Manual J as the national ANSI-recognized standard for producing equipment sizing loads for single-family homes, townhouses, condominiums, small multi-unit buildings and manufactured homes. I have been in this trade 47 years, I hold a Master HVAC License and I am NATE Certified, and the load calculation is still the step I will not skip. A wrong size costs you comfort for the life of the system. Sizing is part of my free estimate on a new system. Call 405-375-4822 and I will come measure the house.

What does a heat load calculation measure?

A heat load calculation measures every way your house gains and loses heat. I measure each room, the walls, ceilings and floors, the insulation in them, every window and which way it faces, the doors, how much outside air leaks in, the people who live there and the heat from appliances.

Then I add the ductwork and the design weather for our part of Oklahoma. Each piece gets its own number, room by room, and the totals give me the heating load and the cooling load in BTU per hour. The room numbers also tell me how much air each room needs, which is how I check whether the ducts can deliver it. Two houses the same size on the same street can come out very differently, because the windows, insulation and attic are different. That is why I measure your house instead of borrowing a number from somebody else’s. Call 405-375-4822 to set up a free estimate.

Why won’t this sizing estimator give me a tonnage?

Because a web form cannot see your house, and a guessed tonnage is how people end up with the wrong system. The estimator above collects the details I will ask about, but it does not print a size on purpose.

Your ductwork, attic, windows and the way the house sits on the lot move the answer more than its floor area does. A number on a screen feels official, and people take it to a contractor and buy to it. If it is too big, the system short-cycles and leaves the house clammy. If it is too small, it runs all afternoon in July and never catches up. Either mistake lasts as long as the equipment does. So use the form to gather your details, write down the model number off your outdoor unit, and call me. I will come out, run the heat load calculation and tell you the size your house needs and why. Call 405-375-4822.

How do you size a shop, daycare, barbershop or apartment building?

I size them with a load calculation too, just a different one. A shop, office, daycare or barbershop gets a commercial load calculation that counts the people in the space, the lighting, the equipment and the fresh outside air the space requires.

An apartment building gets a residential calculation for each unit, because every apartment has its own walls, windows and exposure. A barbershop with dryers running and a full waiting room carries a very different load than a quiet office the same size. A daycare needs fresh air for a room full of kids. A kitchen with ovens or a shop with welders adds heat of its own. Those are the things a floor-area guess misses, and they are why a commercial space can stay hot with a big unit on the roof. Tell me what happens in the building and how many people are in it, and I will size it from there. Call 405-375-4822.