Why Does My Furnace Sound Like It’s Backfiring? Ask an HVAC Expert

furnace sounds like its backfiring

Tim in Sacramento is having somewhat of a scary issue with his furnace this weekend, so he’s reaching out to ask an HVAC expert about it. Tim writes:

“Hey Bell Brothers crew, I hope you all are having a nice winter. I know it gets much busier toward the middle and the end, when basically everyone here in Sacramento is running their furnaces at the same time. I can only imagine how many calls you all have to respond to from now until the weather gets warmer again! Sending positive vibes your way. Now, I’m going to try to save you one potential call today by asking a question instead: Why does my furnace sound like it’s backfiring?

Let me tell you a bit about my furnace. It’s getting up there in years. I’d have to check my records, but I’m pretty sure it’s somewhere between 15 and 20 years old. Also, it just started making that noise this winter, and, to be totally honest, I’m not all that surprised because this is the first time in I don’t know how long that I’ve skipped my annual heating and air checkup with you all. Anyway, thanks for your time, and I look forward to hearing from you!” -Tim in Sacramento

Hey there, Tim! Wow, you certainly did send a lot of kind words our way, words that are much appreciated. This question about why your furnace sounds like it’s backfiring is definitely one we’ve heard often. So, what do you say we do our best today to shed some clarity on the issue, going over why it happens, what you can do about it, and whether it means it’s time for someone with a furnace as old as yours to invest in a new model?

Why Does My Furnace Sound Like It’s Backfiring? It Depends.

Why does my furnace sound like its backfiring?

Of all the things that can go wrong with a furnace or AC, I think a furnace or AC making a loud sound is the one that causes people the most distress. An odd smell or a sudden drop in efficiency is, of course, problematic as well, but there’s nothing so jarring as when equipment deep in your walls starts making noises that you aren’t used to, whether it’s an AC hissing or a when a furnace sounds like its backfiring, as is the case for Tim.

There are a few different answers to the question about why a furnace sounds like it’s backfiring, though. The most common answer is that the age of your furnace may mean that worn down parts are causing gas to backup in a way that eventually leads to a sudden release and boom. We’ll go over this in the next section, but unfortunately for Tim, who was hoping to avoid having to have an HVAC tech out to his home, this is not one of those problems I recommend homeowners tackle themselves. To get to the actual root of this issue, a professional will need to come out and take a look.

What to Do If Your Furnace Sounds Like It’s Backfiring

When a furnace starts to make a boom noise like it’s backfiring, as I noted above, it’s often because of a gas buildup occurring. When this happens, call a professional HVAC tech out to your home to take care of it ASAP.

There are a couple of reasons you don’t want to handle this issue yourself or leave it unchecked for a large amount of time. Chief among them is that any time there is an issue with the gas being supplied to your furnace, it makes for dangerous DIY conditions. The nature of gas is that it’s combustible, and an unskilled tech just shouldn’t be working with it.

Second, you want to call out an HVAC tech right away when you have a problem like Tim’s because, if left unchecked, that boom noise could get louder and louder. The louder the noise, the more gas that’s backing up and eventually being released all at once. If a forceful enough boom occurs, it can crack your heat exchanger and lead to a much more costly repair process.

Getting Your Furnace Replaced If It Sounds Like It’s Backfiring

This last section is a special note for homeowners, like Tim, whose furnaces may be approaching the 20-year range. We’ve talked about how efficient your 20-year-old furnace is before, but this is info that’s worth repeating. Long story short, once your furnace gets to be as old as Tim’s (between 15 and 20 years old), it starts to see a massive drop in efficiency. There are also signs that start cropping up to indicate that it could be time to have it replaced.

We’ve talked about signs your furnace needs to be replaced in the past, and a great many of them apply to old and aging furnaces. Things out of the ordinary, like odd noises, smells, and uneven heating, are all good indicators. Another good indicator is simply the age. By year 20, you really need to start having a conversation about your next furnace, especially given the advances in HVAC technology that have taken place in the past two decades.

I hope that info helped Tim and others hearing odd noises from their furnace. Not that it provides much solace, but it is a fairly common ailment to have. As I said above, I highly recommend that you call an HVAC pro out right away. Odd noises are things that you’ll want to have looked at ASAP.

Contact Bell Brothers to schedule your next furnace check, tune-up, or a free in-home estimate on furnace repairs today. Our “No Surprise Guys” have been serving the Sacramento and Northern California area for more than 30 years. The price we quote is the price you’ll pay—guaranteed.

Image courtesy Wayhome Studio