Today on Ask This Old House. And in most houses like this, twenty to thirty percent of the air in the ductwork never makes it to the living space because of small leaks like this. So today, I'm gonna seal the ducts from the inside. That's next on ask this old house. Well, Mark, your house is just beautiful. Thank you, Rishi. We love it here. So what's up? Well, we wrote to you guys about our heating and cooling system. It's a forced air system. Alright. I can see a supply register right here. That's gonna blow warm air in the winter right against the glass right there. That's good. You should have a return here somewhere. You have a return right around the corner. Alright. So the air goes back to the furnace to be reheated right there. So what's up? Well, we put a new furnace in about eleven months ago. We're hoping for a greater return on our investment. Our utility bills are much higher than we thought they'd be. That's not good. No. It's not good. And, you know, the other big problem here is that we'd like to see more consistent temperatures in the house. Inside the house? Specifically upstairs. Okay. Well, you're not alone. A lot of people with a forced warm air system complain about being uncomfortable. Yeah. It really has been. And, you know, another thing we noticed is that it's just very dusty. There's just dust everywhere. It's very annoying. Let's see what you got. So here it is. You have a furnace. Looks to be gas fired. Yep. Okay. So inside this box, you've got a blower down here that pushes the air up across a heat exchanger. That'll heat the air in the winter. Above it, you've got an air condition coil right here that'll cool the air in the summer. Now that fan pushes the air up into this trunk. Now this trunk right here, I can tell you, is a supply trunk because it's insulated. And you can see right here, there's branches that go up upstairs right there. Looks like you got some other branches. Yep. Branches that go all the way along all the way along right here. Now this ductwork is insulated, but it's not sealed. People see this insulation and say, oh, my ducts are sealed perfectly. Well, I've seen it so bad that when you turn on the furnace, all of a sudden, the insulation blows up like that, which means the air is coming right out. Right. And it's a big deal in this country. You can lose as much as twenty to thirty percent of duct losses where it doesn't actually get up to the place you wanna be. Wow. You lose it to the attic, lose it to outside, you lose it to the basement. Okay? So this is the supply trunk right here insulated, but over here you can actually see really the issue with ductwork. Here's the return coming from upstairs, here's the return right here. When these come together, you can see that the installer has sealed this with a mastic, sort of a rubberized cement to seal up the joints. The mastic is applied with a brush at any place that air could ever leak out. It's messy, but it's really effective. You also could use a foil tape to seal any of the joints that are easily accessible. Look at the challenge. You got a metal trunk, a metal trunk, and the only thing holding it together is this metal cleat, that's not airtight. So your system is not unusual. You've got all this ductwork exposed down here, and what we could try to do would be to seal the ductwork from the outside. Well, it's pretty straightforward on the return side right here. Right? We can get at it. Right. It's not as straightforward on the supply because you have to pull down that insulation, seal the ducts, and then reinsulate. And even if we did all that perfectly, you've still got some great percentage of your ductwork that's actually up inside your building that we can't get at. Right. So it could leak to the attic and everywhere else. So what I actually wanna do is do something new. I wanna show a technology where we can seal every bit of this ductwork perfectly from the inside. Sounds great. Alright. Mark Salon is Steve Taylor. He's gonna help us seal the ducts today. Hey, Steve. How are Hi, Mark. So how'd you get started? So we've already started upstairs. We've sealed all of the supply and all of the return registers. So now any leakage that we measure is coming just from the ductwork. Okay. Great. And then you tested the ducts? We did. We ran a pretest. Okay. So we used the fan in this box K. To blow air into the duct system and see how much air is gonna leak out through the loop. So that pressurized the ducts and you got tied into the computer here. Correct. So how do we do? We lost three hundred and seven CFM cubic feet per minute, and that's equivalent to a hole in your ductwork of about fifty eight square inches. That's a big hole. Wow. So let's do the math. Three hundred and seven CFM. This is a four ton system. That's, like, just under twenty percent. Right? Correct. Okay. So twenty percent is not coming back to be reheated. You're heating your neighbor's house. It's unbelievable. Alright. So how do you seal the ducts? Well, first, we're gonna start with the sealant. So that's a liquid. Is that what this is here? It is. K. Sort of milky. Sort of rubbery. Okay. So, great, how do you get it into the ductwork? It's a liquid. So in order to seal the ducts, we need to do it as an aerosol. So we're gonna use the sealant. We use the same fan that we used for the pretest. Yep. We have a nozzle that injects the liquid into the duct. The small particles that are now in aerosol travels through this flexible duct here to a y branch. Gotcha. Then it can go to the return and the supply and we seal both at the same time. So I understand why we would we would seal the supply but why do we seal the return? Well, think about it, you know, you got heated air coming out here, we want to keep that in the ductwork. Well, on the return side, it's under a negative pressure so it's pulling air in. Remember you complained about dust? Yeah. Well, if these leak and there was any dust down here, it would be sucked into the ductwork and then distributed all into your house. Okay. So all this happens from inside the ducts? It does. We're not gonna actually line all the ductwork. We're actually gonna only seal where the breaches are, the breaks in the ductwork. So we might see a little bit leaking out from right here. In order to prove to you how it works, though, we're actually gonna cut in a hole right here with a screen to really see that work. Great. So with this hole and the window screen over it, I've actually simulated some of the duct leakage you have upstairs in the building. Okay. So we all set to go, Steve? We are. Let her rip. So we'll activate the machine. Okay. The fan will turn on, and it'll start to inject the sealant. Here it comes. Right now, the airborne sealant is flowing through the pressurized ductwork and it's squeezing out just where they have an opening in the ductwork. As it flows through those little cracks, it catches on the crack and actually coagulates to seal any duct leakage. Alright. So we've been running for about ten minutes, and we've gone from three hundred CFM of leakage down to a hundred already, and we're not done yet. Pretty cool. Now any of the steel that happens to leak into the living space can be captured from this scrubber fan onto the filters. Alright. Well, we are done, and now I can actually show you just how effective this was. So instead of the hole, look at this. The window screen where the hole was is completely sealed, and that's really the same as all the leaks in your ductwork. That's cool. Alright. So, Steve, what's our final numbers? How do we do? Well, if you remember, we started off at three hundred and seven CFM, which is equivalent to about a fifty eight square inch hole in the ductwork. Yep. So now we're down to nineteen CFM. Twenty. Great. And that's only a four inch square hole. Well, this is what gets my attention right here, Mark. A ninety four percent reduction in duct leakage. That work for you? Yeah. That's great. I think your whole system is gonna work better too. It's gonna be more comfortable, more energy efficient, and it's gonna be cleaner in the ductwork. Great. Thank you for your great work, Steve. Thanks, guys. I really appreciate Yes, sir.