The Life Cycle of a Furnace, AC, and Heat Pump
Their Life, Death, and the Trouble Between
–
Dame Goodall could describe the life and times of a chimp because she hung around them for most of her life. Well I’ve been fraternizing with furnaces, air conditioners, and heat pumps for most of mine. They usually smell better than chimps and at least one of them can live nearly as long. To understand how your HVAC lives and dies, you need to know just a little about it works.
How Do They Heat and Cool?
During the summer an air conditioner and a heat pump are essentially the same. They both have a compressor at the bottom of an outdoor unit that pumps refrigerant. The refrigerant moves heat from inside your house to outside your house. Neither one destroys the heat in your house. Rather, they both move it outside. Where an AC and a heat pump differ is in winter.
During the winter an air conditioner can’t provide heat, so in our part of the world it’s usually paired with a natural gas furnace. I’ll refer to such pairings as a “furnace+AC”. When a home with a furnace+AC needs heat, the furnace burns gas and the AC is dormant. That means the AC’s compressor is dormant too. As you’ll soon see, that’s a good thing.
During the winter a heat pump provides heat by reversing the AC process. It moves heat from outside your house to inside your house during winter. If that’s a little confusing, you can watch explainer videos. Or just take it at face value that a heat pump is an AC that can work in reverse. That means a heat pump’s compressor runs in summer and winter. That’s a bad thing.
Life is Good: The Furnace and Air Conditioner’s Tale
If a simple furnace+AC system is installed well and properly maintained, then it’s probably going to have few if any problems for the first ten years. Eventually it’ll need to be repaired of course. It may not be cheap to fix. However, as long as you can find an honest contractor, it probably won’t be too expensive either. And of course as time goes by the failure rate goes up a little.
Then, at some point in its twenties or thirties, a furnace+AC may have an unfixable failure. That’s a failure that’s so expensive or difficult that no contractor is willing to fix it. One of the most common examples of an unfixable failure in an AC is compressor failure. Once the compressor fails in an AC that’s over twenty years old, the usual remedy is to buy a new furnace+AC.
The most common unfixable failure in furnaces is a cracked heat exchanger. Once the heat exchanger fails in a furnace that’s over twenty years old, the usual remedy is to buy a new furnace+AC. You don’t normally have to replace the AC with the furnace or vice versa. However, if you’re changing one and the other is old, it usually makes sense to do both.
Locally at least, I’ve found that most unfixable failures in a furnace+AC system happen to the AC first. And that’s with the furnace being used twice as much as the AC! Naturally there are exceptions, especially with extremely complex furnaces. So buy a relatively simple furnace+AC and it just might have a chimp-like lifespan of thirty years or more.
Life is Short: A Heat Pump’s Tale
A heat pump’s life story is going to be similar to that of a furnace+AC, but shorter. It’ll probably have its first repairs in the five to ten year range with increasing regularity as time goes by. And given the modern heat pump’s finicky and delicate nature, its efficiency is likely to drop more quickly than that of a simple furnace+AC system.
Then comes the heat pump’s unfixable failure. Like an AC, it’s often the compressor. And since it’s literally an “AC that heats”, it’s using that compressor for nine months a year instead of three. If an AC’s compressor often dies in its twenties or thirties, how much more quickly will a heat pump’s compressor die with three times the usage? A lot of them will be lucky to see twenty.
It doesn’t help that a heat pump’s heating mode is more stressful on its compressor than air conditioning mode. If converting from a furnace+AC to a heat pump increases compressor usage by a factor of three, it may very well increase compressor wear and tear by a factor of four. That doesn’t mean the compressor will die four times faster, but it WILL die a lot faster.
More Reasons for a Heat Pump’s Early Demise
First, most simple air conditioners and simple heat pumps come with scroll compressors. Most scroll compressors are tough. Unfortunately most contractors are pushing variable-speed heat pumps that come with rotary compressors. Rotary compressors run hotter and have lower fault tolerance. They’re garbage IMO. Get one of those and your compressor may very well die four times faster. I don’t think that will be common, but I’ve already seen it happen.
Second, even if your variable-speed rotary compressor does last, the inverter that drives it probably won’t. What’s an inverter? It’s an expensive, complicated, high voltage, high wattage circuit board that works under extreme conditions outside. What could possibly go wrong? :) I bet most inverters will fail in their teens, if not sooner. Have one of those fail outside of its warranty and that’s when the contractor who installed the failed heat pump just might say…
[Begin Parody]
“This here charcoal spot indicates that your eleven year old inverter has failed. It’s too bad the warranty is only ten years. Uhm, yes. You did pay us for preventive maintenance every year for the last decade with the idea that we would prevent something. Eh, right again. We did sell you a $500 surge protector that cost us $50 with the exact same idea. Sorry. Act of God or whatever.
Anyway, the new inverter costs $4K installed. It supplies the compressor with power, so we can’t test the compressor until after we install the new inverter. Unfortunately our supplier doesn’t take back inverters that have been installed. So if we install it, and if the compressor is bad, you pay for the inverter anyway. Add $6K for a new compressor. You know… ‘sunk cost’.
Even if the compressor works now, it’s going to die soon anyway because rotary compressors are weak. Then it’ll spit out particulate that jams up the reversing valve. That’ll be another $3K. Do you really want to risk $13K on this ‘old’ heat pump? Wouldn’t it be better to put the past behind us and start fresh with a brand new hyper-heat variable-speed heat pump for only $30K?
You are correct. Your previous furnace and AC didn’t have any of these unreliable parts. A new simple furnace and AC wouldn’t either. But, to be frank, anyone who burns fossil fuel hates the planet and loves ‘Big Oil’. If our glorious electrified future requires replacing your HVAC system twice as often as we used to, well that’s a price we’re willing for you to pay! I love the leader!“
[/End Parody]
Yeah, yeah. The Simpsons is so Gen X. Anyhoo…
That’s just as much a prophecy as it is a parody. I’m sure there will be thousands of owners of turbo-heat, hyper-heat, hypno-heat, affinity, infinity, indefinity, variable-speed, green-speed, and I-feel-the-need-for-speed heat pumps who will face situations like that. That might be OK if those owners had made fully informed decisions about their heat pump purchase and, therefore, knew what they were getting into.
Unfortunately many homeowners who convert from gas to a heat pump make underinformed decisions because their HVAC contractors procure the proverbial posture of their primate pals: See no evil, hear no evil, and speak no evil about heat pumps. Instead they ape “Big HVAC’s” heat pump hype and fling them with abandon. Their profit is their motive. Your education is mine. Keeping learning about heat pumps and they just might lose their a-peel.
If you just came from “Heat Pumps Are Inferior”, click here to return or hit your back button.