Robin Jade Conde

PODCAST: Hollow wall anchors and combustion air

Today we discuss direct and power vents and combustion air.

Reuben and Tessa discuss an inquiry about a contractor’s advice to install a direct vent for their water heater replacement. Reuben explains that this was extremely unusual. He defines a power vent and a direct vent. Tessa inquires about changes in the building code.

They also talk about combustion air. Reuben highlights that combustion air is brought into every Minnesota home. Tessa explains what combustion air is. They highlight that combustion air ducts should remain clean and must be checked periodically. 

Reuben shares about spending the weekend with his daughter, Lucy, and talks about a learning opportunity with her.



The following is a transcription from an audio recording. Although the transcription is largely accurate, in some cases it may be slightly incomplete or contain minor inaccuracies due to inaudible passages or transcription errors.



Reuben Saltzman: Welcome to my house. Welcome to the Structure Talk podcast, a production of Structure Tech Home Inspections. My name is Reuben Saltzman, I’m your host, alongside building science geek, Tessa Murry. We help home inspectors up their game through education, and we help homeowners to be better stewards of their houses. We’ve been keeping it real on this podcast since 2019, and we are also the number one home inspection podcast in the world, according to my mom. Welcome back, Tessa, how was your weekend? What’s new in your world? 

Tessa Murry: Hey, Reuben, I’m doing good. I have been working a lot out at the wedding venue. It is, I guess the beginning of wedding season now, and so that’s been keeping me pretty busy, helping prepare for weddings, clean up for weddings, make sure they go smoothly. It’s a whole production. So, yeah, and we celebrated a birthday here, yesterday, it was my sister’s birthday, so that was nice too. And last night, I was up at 1:00 AM to see the Northern Lights.

RS: Are you serious? 

TM: Yes. Yeah.

RS: Okay. So you set your alarm, you got out of bed in the middle of the night, and you are blessed with a clear sky, yes? 

TM: Not exactly, actually.


RS: Okay.

TM: I had attempted to see the Northern Lights earlier last night a couple other times, and I was still awake. It was like, a little after midnight, and then my sister texted me, and she said, “We can see the lights.” And she doesn’t live far from me, so I went out, and then drove to a spot that was high on a hill kind of away from some lights, and then stood out there and watched them for 15 minutes, and it was partly cloudy…

RS: You did this all by yourself? 

TM: Well, I got my parents to come with me too, and so, yes, the whole fam saw them last night, my sister, her husband. Although, my nephew, little Sammy was sleeping. But it was partly cloudy and so they kind of came and went and they weren’t super vibrant, like, they weren’t… You’ve seen the pictures of what they look like when they’re fully visible, they’re beautiful. So this was more just almost like, kind of pulses in the sky of a faint color that was just rippling through the sky. It was really neat.

RS: Okay.

TM: Yeah.

RS: You’re pretty hard core. Did you take any photos or videos? 

TM: I did, yeah, I took a few photos where you can see some lights. It didn’t show up too well in the video though.

RS: Okay. Alright. Well, I gotta see it. I gotta see it. That sounds fun.

TM: That was in the middle of your sleep time, I’m sure, right? You didn’t get up for those? Your sleep is precious.

RS: Oh, very much so, very much. I’m in deep sleep at that point, not to be interrupted.


TM: Yeah, yeah. So, what’s new with you? 

RS: As most people are, I think, Tess. Seriously, 1:30, 1:30 AM. Come on.

TM: That’s true. Yeah, I’m a night owl, I’m a night owl.

RS: Good for you. You are.

TM: Yeah. So what’s happening in your world, Reuben? What’s new? 

RS: Wait a minute, hold on Tess. Before we move on, I wanna revisit our podcast from last week, I think it was last week, we were talking about our tool list for every homeowner…

TM: Yes.


RS: And you sent me a text message, which just made my day. What did you send me? 

TM: I knew it would. My towel rack fell off the wall, [laughter] and so I looked at it and it was the tiniest little screw holding it on, and so I was like, “Shoot, I need a precision screw driver.” [laughter] And I immediately thought of you and our podcast, and I was like, “If only I was like Reuben and I had all these little tools stashed on every level of my house, I would be set.” Instead, I had to search for about 30 minutes and I had to go all through my house, and finally I found a set in the basement, tucked away and I fixed it.

RS: But you had one.

TM: Yeah, had one and I fixed it.

RS: Okay.

TM: But I thought what a great tool and every homeowner should have one of these.

RS: Yes. Yes. I think you were kind of a tough sell on that one, but alright, alright, we won’t have to…

TM: I was like, I use one every few years in here. It was like a week later, I needed one.

RS: Yeah. Oh, that’s fantastic. Okay. I love it, I love it. I spent a lot of the weekend doing a deep dive into my daughter’s room, like, doing a super deep clean, where it’s like, it’s the Kon Mari thing. You just… You empty out everything…

TM: Kon Mari? Who’s Kon Mari? 

RS: And it seems like you declared bankrupt… Maybe not, maybe her name’s not Kon Mari.

TM: Marie Kondo? 

RS: Marie Kondo. That’s it. Yep.

TM: Yeah.

RS: But that’s the method that she has, I think.

TM: Yes.

RS: Or maybe it’s… Her book is called “Spark Joy.” I have no idea what I’m talking about. I’ve seen…

TM: No, I know what you’re talking about, yeah, it’s Marie Kondo, you take everything out of the closet, all the clothes everywhere, and you throw them on the bed, you see what you have, and then you start sorting them, is that what you were doing? 

RS: Yeah, yeah. Yeah, we did such a deep clean, we spent all day on Saturday, my daughter and I going through her room, so that was… That looked good and then…

TM: Dad points for you. Dad points for you.

RS: Dad points. You know what, that just felt like, it was a labor of love, but I’ll tell you what I feel like I got dad points for was, one of the things was my daughter wanted to put these shelves up and she wants to store some stuff, just these tiny little shelves. They’re just these little things and it’s no big deal, a few hollow wall anchors, but yesterday, I was like, “Okay, this is a learning opportunity, because how many young adults do you see putting screws directly into drywall, and it doesn’t do the trick.” And I had built a model wall for some mold experiment that I was trying to do, where I kept saturating a wall over and over again, every day I’d pour water on this wall to see how long it’d take to grow mold. And long story short, I had a miniature wall built out of 2x4s and drywall, and I was like, “This is it, I’m gonna show her.” So, we took it into the kitchen and I was like, “Alright, I want you to drive a screw through the dry wall, now try to pull it out,” and it just pulls right out like, with your fingers. I’m like, “Alright, now put it into the stud.” And like, okay, what…

RS: How far studs are spaced, we got the infrared camera, we looked at the outside walls to see, “Look there they really are, the studs are every 16 inches, let’s measure.” And we got into… It was like an hour lesson on hollow wall anchors about, “Why you need hollow wall anchors and the difference between… It’s nice to go into a stud if you can, but if you can’t, you can use this and here’s how it works, and here’s the drill.” And how to find studs, we went into all that.

TM: Wow.

RS: And I’m like, “Do you know how to find a stud?” She’s like, “Yeah, just use your infrared camera.” I laughed, I’m like, “Most people don’t have a $2000 camera, and you probably won’t either.” So we went over knocking on the wall and using a magnet and stud finder, all that stuff, it was great and I thought…

TM: That’s so amazing.

RS: “I need to record a video.”

TM: Yes, I was just thinking that, I thought, “Reuben, that is such valuable information and there’s so many homeowners or just people out there that probably don’t know those tricks and tips, and why they need wall anchors and all of that.” That would be a really great class.

RS: Yeah, thank you. Okay, good, good, good. I’m glad to hear you say that, ’cause it’s one of those things I’ve taken for granted my whole life, knowing this, since I was like Lucy’s age, since I was a little kid.

TM: It’s like breathing. Yeah.

RS: Yeah, yeah. But it’s like, “I bet a lot of people don’t quite get all of this,” it might be a fun video, it’ll take a long time, but look for that in the future.

TM: You can have Lucy help you. Yes, I love it.

RS: I could.

TM: Yeah. Lucy should help you with that.

RS: You’re right. [laughter] Yeah, that’s a great idea. Great idea.

TM: Oh, that’s cool, very cool.

RS: Alright. So that was satisfying. Love those teaching moments. I was able to hold her interest, probably only because she knew it all ended with her getting shelves, [laughter] it was a little carrot and the stick, but fun to get into that.

TM: Well, and you have a $2000 IR camera. So that makes it fun.

RS: Yeah, yeah, exactly. Everything’s more fun with an infrared camera.

TM: Yeah, definitely. Cool.

RS: Okay, so for today’s podcast, I wanted to talk a little bit about combustion air, because I received an email over the weekend or the office did. I may be fuzzy on the details, I believe, it was a real estate agent who was asking on behalf of his client. His client needed to replace his water heater and hired a contractor to do it, and the contractor said, “We need to put in a direct vent water heater.” Now, the first problem with that is that he surely did not mean direct vent, he said direct vent, but by definition, a direct vent appliance is “Something that takes all of its combustion air directly from the outdoors. It’s a sealed unit, it’s factory-sealed, it mixes the air in the fuel, it burns it, and then it directs the exhaust gas back to the outdoors.” It’s a sealed unit, that’s what direct vent is by definition, that’s what the code book says.

RS: Now, a direct vent water heater is extremely unusual. I won’t say I’ve never seen one, but I don’t think I come across more than one a year, probably not even that. It’s extremely unusual. What he surely meant to say was a power vent water heater. And a power vent is one that it has a fan and it blows the exhaust gas directly to the outdoors, and it will basically never back draft, right? 

TM: Yeah, it’s what you see in all the new construction houses, it’s got one PVC pipe coming off the top of it that vents out through your rim joist typically or out to the side of the wall and takes that exhaust gas out. So it does have a pipe and it does exhaust the combustion gases, but it’s not completely sealed, like a direct vent.

RS: No, no. So, the email said, “Alright, so he’s gotta have a new water heater and his contractor’s telling him all that’s allowed is what he meant to say was power vent water heaters, you can’t replace an existing one.” Tess, I’ve never heard of such a thing. Have you heard of such a thing? 

TM: No, but I guess I’m curious, is there a new code that’s out there now that’s requiring it, either through the building performance or through plumbing or something like that, are you aware of any new code? 

RS: No, and if there was… This is one of those challenging things where it’s like if you wanna find the requirement for something, it’s easy to look in a code book and figure out where it is, but then to find a negative, it’s a lot tougher to say there is nothing that says this. It’s like the old thing about, there was always this rumor that you had to have a closet to call something a bedroom, “How do you prove that there’s none of this in writing anywhere?” That’s a really tough thing to prove, and I think this is the same thing. I’m not aware of any prohibition that says this, and if there were some rule that said, “You can no longer install an atmospherically vented water heater, a traditional water heater,” we would have heard about this, this would be making huge waves.

RS: I just heard recently that you’re no longer gonna be required to install receptacles at islands in kitchens, and that’s mind-bending. “Whoa, this is a huge change, you’ve always been required to do that.” This hasn’t even gone into effect yet, but my mind is blown and we’re gonna be talking about this, and everyone’s gonna know about it before it goes into effect. There’s no way you’d have some gigantic rule change like this on water heaters saying, “They’re no longer allowed by code,” and we wouldn’t have heard about it. Am I right? 

TM: Part of me won’t even… Yeah, it is big… That’s a huge change, what about furnaces? I’m just thinking with a lot of the older type furnaces, is there anything that requires a high-efficiency furnace to be installed, if you’re building a new house or putting in a new furnace? 

RS: Nope. No. Well, for new construction, I don’t know. Boy, it’s been a while since I did the calculation. I think when it comes to new construction, it just makes way more sense to install a high efficiency. I’m certain that there is no prohibition on installing a low-efficiency furnace, if somebody was totally bent on doing it, I think you still could.

TM: It’s almost like with cars, car manufacturers, they’re required to have a certain fuel efficiency, and they get tested for that. And we’ve got certain standards that are out there. The same thing I would think would go for combustion appliances, too, it’s like, the industry is requiring us to up our game and install these more energy-efficient systems that require less fossil fuels. And so, I wouldn’t be surprised if there’s some kind of standard out there that says, “You need a 90% efficient furnace or better.” But I guess, I can’t… I’m not aware of any code that says that same thing for water heaters, so.

RS: There was a national standard, that it got passed, and for a long time leading up to a certain date, and I don’t have my dates, I didn’t research it, I didn’t know we were gonna be talking this deep into it, but for a long time, that was something that was coming, where you weren’t gonna be allowed to install an 80%-efficient furnace anymore. It was all 90% plus, and that day was coming, coming, coming and all the contractors were telling their clients, “Hey, look, you’ve got a townhome and you’re surrounded by neighbors on both sides, and it’d be impossible… ” Not impossible…

TM: Difficult.

RS: “It’d be really expensive to replace your furnace with a power vent or direct vent or high efficiency furnace. So, if you’re gonna be here, you need to get your furnace replaced now, before this goes into effect.” And they’re using it as a sales tool to tell everybody, “Look, if you want the old style, you gotta get it replaced before this date.” And we went right up to that date, and then the rule got overturned, and it never went into effect.

TM: Oh, really? Okay.

RS: If you’ve heard about this in the past, there was a thing, it existed, but it got overruled, so.

TM: Thanks for clarifying that, ’cause I do remember that point in time, I can’t remember what years that was happening, but I remember that, but then it got overruled. So it would be interesting, yeah, I wonder if this is a case where a telephone game where maybe the contractor said something to the homeowner, the homeowner said something to the real estate agent and the real estate agent said something to us and something got missed in translation, but…

RS: Yes, I think that’s gotta be it. I think what the situation probably was, was you’ve got a water heater, an atmospherically vented water heater, it means that it’s using air in that room for combustion, and it’s just relying on the exhaust gases being very hot and therefore very light, and they leave the house through gravity. That’s a very weak way of assuring that you’re gonna get the exhaust gas to leave the house. They probably had a system like that, they probably had a fairly small room that the water heater was installed in, and it probably had a bunch of fans throughout the house that are going to compete for air. And they knew that you can’t just swap out the water heater. I mean, you need to have some way of providing air, and if you don’t, then you’d have to install a power vent. And that’s all very true, you do need to have an air source, but it doesn’t mean you can’t replace the water heater with the same one. It just means you need to make some changes, you need to make sure that it’s safe, if you’re gonna install a gravity water heater, right? 

TM: Yeah, I think everything you said is very true. I just wanna add one thing to that, too. In the weatherization world, a lot of times there was… They do combustion safety testing to make sure that the water heaters were drafting properly, like you said, and there’s this test that you would do. And the Building Performance Institute has a certification for people that go through training to do it, and they put the house in a worst case depressurization setup and turn on all the fans and do that. And we at Structure Tech do that, too, that was part of our training for home inspectors, was to kind of make sure that these natural-draft water heaters are able to vent properly, because if they aren’t, you’re getting all this carbon dioxide and harmful flue gases coming back into your house, so it’s an important thing to check. And there are so many houses that have these natural-draft water heaters, at least where we live, that’s I think the primary type of water heater we run into, unless it’s new construction, where you see the power vents, so it’s relevant. And the one thing I’d add to what you said, though, is that even if you do a test on that day, the worst-case depressurization test and the water heater does okay, it doesn’t mean that it’s gonna do okay tomorrow or down the road.

TM: If the homeowner decides to make improvements or if the weather changes, if there’s wind, what the temperatures are, if they add bath fans, if they add a kitchen fan, or they do an air sealing project, they make their house more airtight, all of those different things can impact our water heater drafts. And so, I would say that you can do that test and you might get “The thumbs up, go ahead. It’s doing fine.” But the safest thing to do, if you don’t ever wanna have to worry about potential backdrafting and you may be making changes or you’re concerned that changes in weather or pressures could impact the water heater if it’s not a super strong draft, then the safest thing to do is to just install a power vent.

RS: True, I agree. It is safer.

TM: And maybe that’s what the contractor would think.

RS: I don’t like a power vent personally though.

TM: Well, yeah, and maybe the contractor came in and said all of that, but what the homeowner took away was, “I have to install this.” [laughter] It’s very possible. It’s complicated.

RS: Yes. Yes. Yeah, I gotta think that it was… It’s exactly, what you said, a game of telephone, and the right message was not relayed. And I wanna just tell you, some of my beefs with the power vent, you can get a natural-draft water heater with a 12-year warranty, power vent, six years.

TM: Six years. That’s true, yeah.

RS: You get half the warranty, they cost more money, you need power to operate them, if your power goes out, you don’t have a water heater, it will not operate, and they’re noisy, you know, every time it kicks on. I don’t like them, I have it at my own house, that’s what I got, and that’s all I will ever have at my own house, ’cause there is no vent at my current house.

TM: Yeah, no chimney for it to vent.

RS: So that’s what I have to do. But I don’t like it.

TM: Yeah. I know. Well, you could update your blog, ’cause you have a good blog out there for anyone that wants to read about it, the debate about the power vents and the natural-draft water heaters, and you bring up valid points and I’m hoping and crossing my fingers some day there’s something better out there [chuckle] than what we have now. And I would say, you know what, maybe we’ll move towards just using on-demand boilers for our water heaters.

RS: That could be, or the heat pump water heaters, we know about those.

TM: Heat pump water heaters. Yes, there’s other options out there, although I can’t say that they’re more affordable, [chuckle] but hopefully they will be.

RS: ‘Cause heat pump water heaters are very expensive, and if you’re going from natural gas to a heat pump you’ll…

TM: Yikes.

RS: I’m pretty sure you will never recover your money, they make sense if you’re going from electric to electric or that’s it.

TM: Or you’re building a brand new house.

RS: Yeah, yeah. That might make sense too. Sure. But Tessa, let’s just talk briefly about combustion air, I don’t know that we’re gonna cover all of it, maybe next week, we could kinda do a deep dive into combustion air, but just to cover the basics of this, because you have combustion air brought in to just about every Minnesota Home. And I know that in other parts of the country, we go to conferences and whatnot, and we’ll talk about this, and home inspectors get this glazed look, like, they have no idea what we’re talking about. So I know this doesn’t exist all over the country, but Tessa, how would you describe a combustion air duct? 

TM: Well, typically it’s just a round duct that… It’s like about six inches in diameter that is in a flexible tube that you’ll find somewhere in your basement that’s connected to the outdoors. And on the outside of the house, you’ll see some type of little hood or vent terminal on the outside, and if you look underneath that, then you’ll see… You should see a screen hopefully. But it’s just a open duct that connects the inside of your house to the outside of your house that allows fresh air to come in, and it’s required for the proper functioning of your combustion appliances.

RS: Yeah, yeah, that’s well put. And it’s like you said, it’s a flexible duct, it’ll always be insulated. And if you’re doing a code calculation to figure out what size of duct you need, for most Minnesota homes, they tell you you need to have a 5-inch duct. As long as you got a 5-inch duct, that’ll satisfy just about all the requirements until you get into some crazy stuff, and then they say, but if you’re gonna use flexible material, you need to increase the size of the duct by an inch, and that’s why you always see exactly what you describe the 6-inch duct, ’cause when you go to flex you need to increase it an inch. And so, that’s what we almost always see is this flex-insulated duct that drops down in the utility room, and then a lot of the time people… Just so you don’t have cold air dumping onto the basement floor, people will make a little J at the bottom of it, kind of like a little trap, so the air has gotta actually rise up to come back in. I don’t know how much of a difference it actually makes, I’d be interested in doing some testing on it to figure out…

TM: Ooh, a little experiment.

RS: How much of a difference it really makes, I probably won’t, but I am curious. You know what I got at my house, Tess? 

TM: What? 

RS: I got the weirdest thing. It is so frustrating. Maybe you’ve got a suggestion for me, I’ve got… In the winter, I’ve got a cold spot on my living room floor, it’s freezing cold, and it’s right in the middle of the living room and it’s all finished space below me. I mean, it’s all basement below me.

TM: Okay.

RS: And I can take it with the infrared camera, it’s just solid blue in the middle of winter and you step on it, you can feel it with your feet, I’m positive that… That’s exactly, I know, that’s about where my combustion air duct runs. I think it’s separated or it’s got a huge hole in it, and there’s cold outdoor air that leaks out into the floor space, or what would be the basement ceiling space. And there’s nothing I can do about it, unless I decide to cut open the basement ceiling. What would you do, would you fix it? 

TM: Well, I guess, how uncomfortable is that cold spot for you? Put on slippers, that’s gonna be the easiest thing.


RS: You never stand there. It’s a travel path, it’s just “Oh, that one step was cold.” So, it’s nothing more than a slight nuisance. The only thing is that I know that a bunch of the combustion air isn’t actually making its way into the utility room…

TM: Where it needs to go.

RS: It’s going into the ceiling space, which is technically connected to the utility room, so the air is getting there, it’s just not traveling inside the duct like I would like it to.

TM: Man, I wanna cut open your ceiling and see what it looks like…

RS: Does it matter? 

TM: Yeah, it probably doesn’t matter in terms of just the functioning of the combustion appliances, it’s getting there, it’s got the air it needs. But I’m just thinking in the summer time, reverse the situation. If you’re pulling in really hot humid air in your air conditioning, in your house and your floor cavities are cooler, if you’ve got duct leakage or anything like that, you could end up with potential condensation issues, maybe.

RS: Yeah, that’s true. Alright, yeah, I’ll leave it alone. Some day, if I tear it open, I’ll take pictures, I’ll share them with you. We’ll know what it is.

TM: Another idea, you know the stuff they use to seal ductwork in new construction, they use like a duct blaster and they blow this material through the ductwork and it finds little holes and it seals it up? 

RS: Yeah.

TM: I wonder if they can do that to your… Or just put a new… Slide a smaller liner through the inside of what’s already there, snake it through.

RS: Start at the outside and snake it through.

TM: Yeah, snake it through.

RS: Yeah, yeah, that’d be interesting. Or I could always get one of our sewer inspection cameras to see if somebody could…

TM: Yes, to scope it.

RS: Beam the sewer inspection camera through there and scope it.

TM: Yes.

RS: Alright. Alright. I might.

TM: Oh, my gosh, we are such nerds.

RS: We are such nerds.

TM: But I’m getting excited thinking about all the different things we could do.

RS: Alright. Well, I’ll keep you updated, but bottom line is, just about every Minnesota home has one of these combustion air ducts, and on the outside, it should remain clean, it’s something that homeowners need to check on periodically. And on the inside, it needs to remain open, don’t stuff any towels in there. I know you’re gonna feel cold air coming in your house, but it’s air that needs to come in, and if you’re having an older appliance replaced, your contractor may need to put one of these ducts in to make this, I wanna say, a code-compliant installation. But as home inspectors, we’re not super concerned about code, we’re concerned about safety, so I won’t say code-compliant, I will say to make it a safe and properly functioning installation.

RS: You may need to have a combustion air duct added, and it’s not a piece of cake to put one of these in in an existing house, you need to cut a hole in the side of your house, probably going through your rim joist. I mean, that’s a lot of wood you’re cutting through, you need to put a register there, you need to put a big insulated duct, and if you’ve got a finished basement, you gotta pass through finished space, that’s a pain in the butt.

TM: I mean, that… The cost of that is… Yeah, it’s gonna hurt. I wonder how many contractors out there installing water heaters actually do that though? Do the testing, say you need to put it in and do it if it’s not already there? 

RS: Well, at some point, I wonder where the cost to install a power vent is actually gonna be less, than putting one of these in, and then they say, “Well, this is code, I have to.” And then the client hears, “Oh, it’s just code to install a power vent.” Maybe we figure this all out by talking through it, Tess, I don’t know.


TM: It’s very likely, it’s very likely. As we know in this industry, a lot of times you tell the homeowner something, and by the time it makes it back to the real estate agent, it sounds completely different, so it’s very feasible.

RS: Yep. Yep. Alright, well, that was a fun discussion, Tess, maybe next week we will do a deep dive, we’ll talk more about combustion air ducts, or maybe not, I don’t know, we’ll see what’s on our mind next week. But I think that’ll wrap it up for this week. Thanks for recording with me, Tess. I appreciate it.

TM: Hey, this was fun, and thanks everybody for listening, and if you have any comments or questions or ideas for topics, how do they reach us, Reuben? 

RS: Please email us or visit us online. You can go to, and that page goes right to our podcast information, you can see all the show notes, all that other fun stuff.

TM: Cool.

RS: Alright. Thank you for listening, everyone. Take care.