LESLIE: Well, many older chimneys serve their homes well but over the years, they’ve become unsafe. A main reason for this is the lack of a chimney liner.
TOM: Well, fortunately, new liners can be installed into old chimneys, making 
them usable, once again, for a variety of purposes, including heating systems and fireplaces. Richard Trethewey is the plumbing-and-heating contractor on TV’s This Old House and he joins us now with tips on how to do just that.
Hey, Richard.
RICHARD: Hey, guys. How are you today?
TOM: We’re doing well. So what, exactly, is a chimney liner and why do we need one?
RICHARD: A liner is just as it describes: it’s some sort of material, either clay or metal, which fits inside of an existing chimney. If you looked at a masonry chimney on the outside of a building, it’s usually brick that you see on the outside. And if we just relied on the brick, we would worry about flue products leaking out through the mortar joints and we’d worry about actually, also, so much cold air being against those bricks that the flue products wouldn’t want to leave the chimney.
A liner is really important for two things. One is to make sure the products of combustion – and that includes creosote, one of the byproducts of wood burning, or some of the carbon that’s in oil exhaust – gets completely up and out of the chimney and doesn’t build up on the inside where you could cause a chimney fire. So, liners are important for that. But also, it’s important to make sure we have proper draft inside of it.
LESLIE: So, now, what are these liners made out of? You know, I know we recently had ours replaced because when we had our standard service, everything was opened up for cleaning and crumbled-up pieces of clay were at the bottom, which was a failed liner.
RICHARD: Right, right. Yeah, right.
LESLIE: So, do you go for a new clay one? Do you go with something more like a metal or an aluminum one?
RICHARD: Well, there was a time that the only product was that clay liner. It was usually 6½x6½ on the inside diameter, sometimes 8×8. And it was built at the time that the chimney was first installed. And if it did crack, you would try to repair it and things like that.
Well, later, materials were available – both stainless steel and aluminum – where you could have a metal liner that was corrugated. Now, I’m not a big fan of aluminum as a material inside of a chimney. Aluminum is not a noble enough metal to take the products of combustion. So if you’re going to use a liner, it always should be this stainless-steel liner that can be pulled in in a retrofit.
Now, the best …
LESLIE: I mean it’s kind of interesting to see them do it. It’s like …
RICHARD: That’s right.
TOM: Sort of snake it down from the top, right?
LESLIE: Yeah.
RICHARD: That’s right. Now, the best liner is actually a straight liner – a smooth liner – that goes in sections that you drop down. But many times, the existing conditions don’t allow you to drop because it’s not always straight. And sometimes, there’s protrusions on the inside where the old liner was.
But when I have my druthers – and I’m going to go with conventional efficiency equipment – I’d love to see a nice, smooth, stainless-steel liner that’s connected together and dropped down into place. And now you’ve got nothing to stop the flue products from going out. It helps to insulate a little bit.
At the next case, it would be the stainless steel. At the least case would be the aluminum.
TOM: And this is equally important for, say, an upgrade to a higher-efficiency heating system, as well as, say, taking a really old fireplace and making it usable once again. Because perhaps it never had a liner.
RICHARD: That’s right. Many of them didn’t and that’s why you read through history about so many fabulous older homes that have burnt to the ground. Because sooner or later, that unlined chimney, the creosote is so rich in between the joints that it’s nothing but a big fire stick to light it up.
Now, as we get more and more efficient in our equipment, there’s an important call-out (ph), an important distinction that when you have efficient equipment, it means we’re getting more and more of the heat that we bought and burned into the building and less is going up the chimney. So, now, if I was going to use a conventional, modern, high-efficiency furnace or condensing appliance – what condensing means, it gets so efficient that there’s hardly any flue products left.
If I put that into a regular clay or even a metal chimney, if it’s too big, there’ll be no choice but condensation or water to rain on the inside of the chimney and the liner. Now, you’ll see – at the base of your chimney, you’ll see water and you’ll say, “It’s not even raining. Where did this water come from?”
TOM: Big puddles, yeah.
RICHARD: And it really isn’t. It’s a byproduct of being really efficient. So all the modern appliances have to have a non-metallic liner. You’ll see it. It’ll be done with polypropylene plastic. I’m not a big fan of PVC; I’d rather have a higher-grade of plastic for those flue products. In that case, they’ll use the existing chimney as a chase to run that plastic vent up and out. And nothing beats putting the flue products up and away. I prefer to do that than to see another tailpipe on the outside of a house where you’re seeing flue products all the time.
TOM: Right. We’re talking to Richard Trethewey – he’s the plumbing and heating contractor on TV’s This Old House – about the value of adding liners to chimneys.
So, Richard, how do you know when it’s time to add or replace a liner?
RICHARD: Well, if you’ve got an aged chimney and you suspect that the liner might be – it’s really time to have a professional – some chimney professional – to come and look at it and do an inspection. They will get up on top of the roof, they’ll come down and they’ll put a camera down inside. That’s another tool that didn’t exist 15, 20 years ago.
TOM: Years ago, right.
RICHARD: You know, now you’d look down with a mirror in the old days.
LESLIE: Yeah.
RICHARD: With this, it’s amazing. You go down, you can take a videotape of it. You can see where the cracks are, you can see where the buildup is. So that should be done.
And if you use your fireplace a lot or if you have a chimney that is working hard, you shouldn’t overlook doing this once a year, maybe once every other year. You should do it enough that you’re not in an unsafe condition.
TOM: Good advice. Richard Trethewey from This Old House, thank you so much for stopping by The Money Pit, Rich.
RICHARD: Great to be here.
LESLIE: Alright. You can catch the current season of This Old House and Ask This Old House on PBS. For local listings and step-by-step videos of many common home improvement projects, visit ThisOldHouse.com.
TOM: And This Old House is brought to you on PBS by State Farm. Like a good neighbor, State Farm is there.
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