The most common furnace mistakes I see in Pittsburgh basements
After decades walking into Pittsburgh basements, the same handful of furnace mistakes keep showing up. Here they are, and how to avoid them.
The most common furnace mistakes we see in Pittsburgh basements are undersized ductwork, filters that never get changed or are the wrong size and type, intakes pulling combustion air right out of the basement instead of being properly vented, and a furnace that is simply oversized for the home. Most of these come down to one thing, somebody skipped the load calculation and guessed. Get the sizing right, get the air right, and a furnace will run quiet, efficient, and last.
Why do the same furnace mistakes keep showing up in Pittsburgh?
I have been in more Pittsburgh basements than I can count, and I will tell you, the same problems keep coming up over and over. It is not bad luck. It is contractors taking the easy way out instead of doing the homework. The industry we live in is closer to the wild West than most homeowners would believe, and a lot of how your furnace ends up running comes down to who you hired, not the codes on the books.
Here are the four I see most, and what each one actually does to your comfort and your equipment.
Mistake 1: undersized ductwork
This is the big one in Pittsburgh, and almost nobody talks about it. A furnace can only push as much air as the ductwork lets it. If the ducts are too small, you choke the system. You get high static pressure (that is the back-pressure the blower fights against), noisy registers, rooms that never get comfortable, and a furnace working way harder than it should.
No company knows how to size ductwork like we do. We have gone through extensive out-of-state training over the years specifically to get duct design right, and we deliberately lower the air velocity at the equipment so the system runs quieter, moves air better, and filters better. Custom ductwork done correctly is one of the biggest differences between a Wahl install and the other guy.
Mistake 2: the wrong filter, or one that never gets changed
I cannot tell you how many filters I find that are filthy, the wrong size, or the wrong type entirely. A plugged filter starves the furnace for air, drives up your static pressure, and shortens the life of the equipment. The cheapest thing you can do to make any system last longer is change the filter on schedule and use the correct one for your setup.
Mistake 3: combustion air pulled from the basement
An older furnace needs air to burn fuel safely. I keep finding setups where the intake is just sucking air out of the basement and the unit is not properly vented. That is a safety issue, plain and simple. A furnace that is short on combustion air or fighting a bad vent is a furnace I do not want in anybody’s home.
Mistake 4: the furnace is oversized
This might be the most common of all in Pittsburgh, and it is the one homeowners ask for on purpose, thinking bigger is better. It is not. When a furnace is too large, the heat cannot leave the heat exchanger fast enough, and the heat exchanger burns up prematurely. It can short cycle, the unit fires, overrides its own safeties, shuts off, the blower keeps running, then it fires again, over and over. I wrote a whole separate piece on the oversized furnace problem because it deserves it.
How do you avoid all of this?
- Insist on a real load calculation, not a rule of thumb or matching whatever was there before.
- Make sure the ductwork is evaluated and sized, not just bolted onto the new furnace.
- Use the correct filter and change it on schedule.
- Confirm the unit gets proper combustion air and is vented to code.
- Have the static pressure checked at startup. If your installer does not know that number, that tells you something.
If you want the honest, no-pressure version of how to choose the right unit, we put it all in our guide on how to pick a furnace. And if you are shopping gas furnaces for an older Pittsburgh home, we know exactly what to look for.
The quick version
- The four mistakes we see most: undersized ductwork, the wrong or dirty filter, combustion air pulled from the basement, and an oversized furnace.
- An oversized furnace burns up the heat exchanger and short cycles. Bigger is not better.
- Undersized ductwork chokes the system, makes it loud, and leaves rooms uncomfortable.
- Most of these trace back to a skipped load calculation. Insist on one.
- Changing the right filter on schedule is the cheapest way to make a furnace last.
Almost every furnace headache I find in a Pittsburgh basement comes down to somebody guessing instead of doing the math.
Bigger is not better, the ductwork matters as much as the box, and the filter is not optional. Get those three right and your furnace will outlast the people who installed it.
David WahlCEO & Master Plumber, Wahl Family
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Call 1-855-GET-WAHLFrequently asked questions
Is an oversized furnace really a problem?
Yes. When a furnace is too big for the home, the heat cannot leave the heat exchanger fast enough, so it runs extremely hot and burns up the heat exchanger early. It also short cycles, firing and shutting off again and again, which is hard on every part of the system. Right-sizing from a load calculation is the fix.
How often should I change my furnace filter in Pittsburgh?
It depends on the filter type and your home, but most 1 inch filters need changing every 1 to 3 months, and thicker media filters can run longer. The bigger issue we see is the wrong size or type of filter altogether. A clean, correctly sized filter protects the blower and keeps static pressure where it belongs.
Why does undersized ductwork matter so much?
Your furnace can only move as much air as the ducts allow. Undersized ductwork chokes the system, raises static pressure, makes the registers noisy, and leaves rooms uncomfortable while the equipment works overtime. Proper duct sizing is one of the most overlooked parts of a good install.
What is combustion air and why does my furnace need it?
A gas furnace needs a supply of air to burn fuel safely and vent the exhaust away. We sometimes find intakes simply pulling air out of the basement with no proper venting, which is a safety problem. The unit needs adequate combustion air and a vent that meets code, every time.
How do I know if my furnace was sized correctly?
The only honest way is a load calculation that accounts for your home’s size, insulation, windows, and layout. If a contractor sized your furnace by matching the old one or eyeballing the square footage, there is a real chance it is oversized. We are happy to evaluate an existing system and tell you the truth.
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