Chimney Liner

[bill kurry]

I have been told that a brick or masonry chimney (even if its an inside chimney) needs to be lined when it no longer has a furnace vented into it but still has a water heater. Is this true?

[BaldLoonie]

The National Fuel Gas Code sez:

if the flow area of the chimney is more than 7 times the outlet area of the water heater draft hood, line it.

Unless it is a high BTU model, it will have a 3" outlet. That's around 7 square inches. Times 7 and you get 49 sq in. Under the above rule, if the chimney tile liner is 49 sq inches or less, you can skip the metal liner kit.

On the other hand, I saw a job with a 75K input Rheem Tripower with a 4" outlet alone on an inside masonry chimney. Wouldn't vent til a 4" liner was installed. Go figure!

[berad]

Code aside, it's generaly always a good idea to line masonary chimney when gas appliances are vented into them. At the very least have the thing inspected anualy, I've seen many chimnies with mortar the comes apart or has a clay liner that deteriorates and allow CO into the house and causes moisture problems in the walls and structure of the house.

[t527ed]

liners are cheap and easy for the protection they give.

[dec]

Thats suprising to me that you can get away with having a liner 7 times the size of the water heater flu. I would be suprised it would vent. I know a lot of shops dont line chimneys if they have a liner but I was always taught to shrink them down so that they will hold heat to vent better. Now I would think if it is that cold outside it would have a hard time ever venting if its that oversized and that cold out. .....am I wrong?

[berad]

You size the liner according to the total BTUH going into it. I don't even remember which regulatory commission presides over it any more. Whomever it is they made a nice little reference chart for flue sizing and combustion air sizing. It's handy. I'll look in my truck if I remember and tell you whom the regulatory body is on venting. Probably National fuel and gas code.

[BaldLoonie]

The 7 times rule is in the 1999 National Fuel Gas Code, 10-1.8

[millerman]

You have to check your local codes first. Ours state you must install a liner for natural gas equipment period.

[bertrand]

What material you guys using for liners - Stainless steel or Aluminum?

[Irishmist]

I am going out on a limb here and guessing that you have eliminted the furnace that earlier common vented into the masonry flue with the water heater. Perhaps you updated to a high-efficiency or for some other reason, the furnace is sidewall vented. I can tell you there are specific vent tables that indicated what size you can stub into with just the water heater.

Almost always, the remaining masonry flue is larger in size than is stipulated for the remaining hot water heater alone. What happens is that there is not enough thermal velocity (heat rising) to carry the by-products up and out of the top, and condensation occurs somewhere in the vertical heighth of the masonry flue.

Options that are available to you should be discussed with your contractor, and he can best advise you as to the correct course of action. Be aware, there are strict guidelines for the installation on liners, and in order for the liners to operate properly and for the anticipated length of time, these guidelines must be followed. There is more to it, than simply threading the liner down and out.

[millerman]

Mr. Lloyd is right on the mark. With the condensation issue you will get black nasty goo spilling out where it can, quite possibly there was an oil fired unit in there at one time. With the liner you must clean the chimney before installing.