Installing an Air Tight Chimney Cap to Stop Air Leakage

In this specific job, Dr. Energy Saver was called in to help this home owner cut energy loss while enjoying the heat of a very peculiar fireplace configuration. His fireplace was fitted with a wood stove, and a stainless steel chimney pipe ran through the masonry flue. In homes with a fireplace, the chimney is one of the biggest air leakage sources in the entire structure, regardless of whether the fireplace is lit or not. Heated air in the living space tends to rise towards areas with colder temperature, and the flue from the fireplace to the top of the chimney is basically a hole in your house providing the ideal escape route for heated air. Closing traditional chimney dampers will not stop air leakages because the typical cast iron damper doesn't seal too well and allows air to get by.

Eliminate The Excess Air Leakage

This is Larry Janesky from Dr. Energy Saver. When we are trying to eliminate the excess air leakage in a home, to make it more energy efficient, one of the biggest leaks we find is up through a fire place. From the flue to the top of the chimney is basically a giant hole in your home. Now there are dampers that close in the firebox, but often people don't close them and even when they do they're cast iron and they don't seat well.

Chimney Caps

There are several different kinds of chimney tops that would work. Today we use the flip top simply because the size that we had in that particular model, but this, is a spring top and it uses pretty much the same type of hardware. In fact, exactly the same type of hardware and you will run the cable through here with a knot on top and when you pull this down it closes tightly for your seal, either one works equally as well. Another advantage of these locked tops is that they really can't be seen. When this one is down you can't see it from the ground. The flip top, when it is closed, you can't see it from the ground compared to something like this, which wasn't air tight at all and is pretty ugly compared to your really nice masonry chimney.

Chimney Cap Sealed Tight

We have our cable from our chimney cap. If I pull on this I could hear it close up on the top on the top of the chimney just 30 feet above here. I am going to put a bracket here so that the homeowner could pull it down, close it and lock it down. Here we are in the final product, pull the chain you could hear the damper close and lock it down. Now this will stop the air leakage out of this chimney when this stove is not being used.

Read Full Video Transcript Below:

Hey, This is Larry Janesky from Dr. Energy Saver. When we are trying to eliminate the excess air leakage in a home, to make it more energy efficient, one of the biggest leaks we find is up through a fire place. From the flue to the top of the chimney is basically a giant hole in your home. Now there are dampers that close in the firebox, but often people don't close them and even when they do they're cast iron and they don't seat well.

Now in this homeowner's house he put a wood fire place insert or wood stove and it has a stainless steel flue inside the masonry flue all the way up to the top. There is a cap that gets put on and this is very loose here. Air is just coming right out of the top. You can never get these caps to seal properly on top because the stainless steel pipe inside the chimney will expand and contract as it gets hot, or cold. So, we know that, for example: a 40 foot, aluminum rain gutter will expand and contract as much as an inch between summer and winter. That is just with outdoor air temperature changes.

Here, we are talking about temperatures between - maybe 80 degrees and 500 degrees. So, that stainless steel pipe will really expand and contract, or break the seal on the top of the chimney. What we are going to do here is, fix the problem with an air tight chimney cap that won't come lose. We are going to install this air tight cap, instead of that one. This one has a cable that runs down the flue and it will hook to a bracket on the inside of the firebox. When the homeowner pulls on the table it will close this air tight cap, effectively sealing his chimney. When he wants to use the wood burning stove he unhooks it from the bracket and it falls open. There are several different kinds of chimney tops that would work. Today we use the flip top simply because the size that we had in that particular model, but this, is a spring top and it uses pretty much the same type of hardware. In fact, exactly the same type of hardware and you will run the cable through here with a knot on top and when you pull this down it closes tightly for your seal, either one works equally as well. Another advantage of these locked tops is that they really can't be seen. When this one is down you can't see it from the ground. The flip top, when it is closed, you can't see it from the ground compared to something like this, which wasn't air tight at all and is pretty ugly compared to your really nice masonry chimney.

The cap that is here is on the end of a stainless steel pipe. For many, many years they would put the stainless steel flue up the masonry flue in a situation like this they would only stick the stainless steel pipe up the masonry flue pipe maybe 5 or 6 feet and then just let the gases come out of the pipe and go up the masonry chimney. But the argument was that the masonry chimney is cold. It has got a lot of thermal mass and is cooling the gases. You are getting creosote build up on the inside of the masonry flue and also losing a bit of your draft. Many millions of inserts are done that way. If the flue comes all the way to the top then the gases can get all the way out and they don't slow down or build up creosote on the inside of the flue. What we are going to do is a little bit of a combination. I cut the stainless steel flue pipe about 8 inches below the top of the masonry flu. Now, we have room for our chimney top cap to operate and the stainless steel pipe is still 35 feet above the wood burning stove. All right, so now we are going to use the silicone sealant, provided with the kit. I don't want to miss any, or make any, gaps because that will cause an air leak. We will set that right on our silicone. The top of the chimney is obviously out in the elements and when water gets inside the cracks of the chimney it will freeze making those cracks bigger and bigger. Eventually, you have chunks of the crown coming off and bricks coming off. Now, I can feel warm air coming out of here from the living space and that is the air, we are going to stop.

Okay, so here we are down at the fireplace. We see our wood stove insert and the homeowner put this into burn wood, obviously, you know the ambiance, the esthetics, are nice, but, also to create heat. The problem is this stove will create heat better outside the house than in. We have, inside the firebox, a damper, that is a big rectangle shape and we open the damper and we close the damper without the stove in here. With the stove in, we shoved a 7 inch stainless steel pipe all the way to the top and we have to open that damper all the way. Basically, a round peg in a square hole. This leaves big spaces on the left and right of the pipe for air to constantly go up the chimney. So, on a day like today, warm air from the house will go up the chimney carrying heat, from the house to the sky. This is a big open hole from here to the sky and there is no way to seal it.

Now, with the stove running it's pulling air, for combustion, into the stove and sends it up the chimney, that's bad enough. We made it worse because of holes around the damper and when that stainless steel pipe heats up, the flue heats. Air will rise even faster because it is being heated and we get air loss from inside the house around the flue and inside the flu both when the stove is running and just around the flu when the stove is not running. What will happen is, when this stove is running, all the air is leaking out of the house. It will be warm here from the radiant heat from the stove, but if you go to the far ends of the house you will have windows that are leaking, more doors that are leaking, and more ducts that are leaking, more because new air from the outside has to come in to replace the air that left. So, really you are paying a penalty by running the stove. You are making this room warmer, but you are making the rest of the room colder, not good.

We have our cable from our chimney cap. If I pull on this I could hear it close up on the top on the top of the chimney just 30 feet above here. I am going to put a bracket here so that the homeowner could pull it down, close it and lock it down. Here we are in the final product, pull the chain you could hear the damper close and lock it down. Now this will stop the air leakage out of this chimney when this stove is not being used. I want you to make a big difference in the comfort, the drafts and the fuel bills in your home forever. If you have a house that you would like to have us take a look at; we can make it more comfortable and less expensive to own, call Dr. Energy Saver, we love to help you. Contact Dr. Energy Saver for a home energy evaluation and written estimate.