In Episode 60 of The Ask Derek Cole Show, Derek Cole answers two common homeowner questions. First, he explains why furnace heat‑exchangers crack, describing how material choice (aluminum, steel, aluminized metal) and manufacturing design create weak spots, especially at curved sections. He contrasts brands, noting that Carrier and Trane are more prone to cracking at these unreinforced curves, while Goodman reinforces the curves and offers a lifetime heat‑exchanger warranty. Second, he strongly advises never to close supply vents in any room. He explains that homes are engineered for a specific airflow balance; closing vents creates pressure resistance, forces the blower to work harder, reduces efficiency, and can lead to uneven conditioning of exterior walls. He also mentions that closing doors can be acceptable only if adequate return airflow remains. Throughout, he stresses regular furnace maintenance to detect cracks early and keep the system operating efficiently.
Chapters
Hey, on this episode we talk about closing the vents in your home and what causes my heat exchanger to have a crack.
What causes the cracks to form in my furnace's heat exchanger?
Depending on the brand you have, depends on if you have aluminum, steel, or just kind of aluminized metal. So depending on what you have depends on how it's formed and depends on where cracks set. So a Carrier will crack differently than a Goodman or a Trane because they're made differently. Now what the Goodman product does is it actually reinforces the weak side. So if you see their heat exchanger, it actually goes like this, like a tube, but they reinforce all the curves because what happens is every time you curve that metal gets weak. It's a weak spot. So usually what you see cracks or failures in, or anything were to rust or crack, would be in those weak spots, which would be the curves, the edges, because it's not reinforced. Um, that's one reason why Goodman gives a lifetime warranty on their heat exchanger for a gas furnace is because it doesn't fail because it has this reinforced edge on each of the weak spots. So as it gets hot, of course, it expands. As it's cool, it contracts. So you get enough of this going on, eventually it's going to get weak enough to crack. So it's always a good idea to have a maintenance done just to check all this out to make sure you're not in that spot where there is a crack and you could be having a problem.
How often should I close the vents off in rooms that I don't use?
Yeah, I get this question quite a bit. You should close the vents off. Never, ever, ever close the vents off in your house. Your house is made and designed to condition with those amounts of grills or runs in that room or in that space. So you should never close off that room, close the door to that room. Well, I'll take it back. You can close the door if you have enough room for the air to get back to the return. So you go into some houses and they have really thick carpet. You close the door and you have to kind of slam it shut. Okay, well, air is going to have a hard time getting through that space. And some homes have a good undercut under the door. So you close it and the air still flows out. So what goes in must come out. Same thing here with air. If it goes into the house, it must come back to the return. So you want to make that as easy as possible because air is like water. Again, it's going to get— it's going to get the air. You want to get it clean conditioned air versus air from outside, crawl space, through the walls. You can't control that unconditioned air. You can control the air in your house. But to get back to the vents, yes, never ever close the vents. So the reason you have vents on the outside of your house is because it's trying to take care of that perimeter. So you don't see— unless you're sitting in a mobile home that has two tracks of duct system, you will not see a grill on the inside wall in your house because it wants to take care of the perimeter outside wall that is affected by the weather. So closing off the grill affects that. Also affects the airflow going into the room. So if I have a split unit and my fan coil is blowing the air out and where it's blowing to cannot get out, what is the air going to do? It's going to try to come back, maybe. So that fan has to work harder to push it back out. Because it's getting some resistance because the vent's closed off, that's going to cause a problem. So if the fan has to work harder to get the air to where it needs to go, is it saving you money or costing you money? Right, it's costing you more money because the fan's working harder. And with this equipment, you want it to work as easily as it can. That's why you need to do maintenance and have it clean. That way it can operate normally and efficiently and the way it's supposed to and not have the added pressure of more air strain coming back to the unit. So I would never close off the vents, and I would never use the— you go to some houses, you see the little plastic diverters, you know, blows the air in the middle of the house. Again, another bad idea, because if you were to do a smoke test in your house What you would see is when the air comes out of the grill, you'll see it go up to the ceiling and then fall down the wall. It's trying to condition that outside wall. So by pushing it to the inside of the room, it's not doing any good. So I would stay away from that and never close your vents. So it's never okay. I don't care. It's never okay. All right, that's it. Episode 60. Got a little serious there, but Really, I get the question a lot. When can I close the vents? I don't use this room a whole lot. Is it okay to close the vents? No, it's never okay to close the vents because you're causing more problems than what you're trying to solve. What you're trying to do is, because you're not in that space, you're trying to get that air back in the spaces you are in, and it doesn't work that way. I mean, it's not made to operate in that fashion. So Again, you have to do what the system is designed for, which is to condition the whole home. It's all sized properly and all the air is on the outside condition. It's trying to get that wall conditioned so you don't— it's not hot, it's not cold, you're good to go. So if you close it off, you're causing more and more problems.
