I have a friend who just bought a cottage with an old airtight wood stove. This stove has an 8" flue, with double wall black pipe to the 8" stainless Selkirk metalbestos chimney. I believe the chimney is about 25 years old, but looks to be clean and in good shape. The stove burns well as she has had several fires and it seems to work well. The problem is that the wood stove is not certified by either UL or CSA, and the insurance company has said that it must be replaced with a new, certified stove. No problem except that all new stoves seem to be 6" flue, and the existing chimney is 8". Can a liner be added to the chimney to make it 6" or must the chimney be replaced as well?
Thanks for any input.

Have you considered just replacing the stove and using the 8 inch certified chimney with an adapter from 6 to 8. It can be done depending upon the way it is installed.

Thanks hvac1000 for your reply.
When my house was built, 9 years ago, I asked the contractor to install a chimney for a wood stove that I did not have yet at the time. He installed a 7" metalbestos chimney, and every stove I looked at to buy was 6". The store where I bought it said that it would be OK as the maximum limit for creating a good draft is 1" over the stove flue size. I have had some trouble over the years with back draft and have found that if the fire is really going, I am OK, but it struggles to burn when I reduce the air intake to the stove for slowing down the burn, after all it is an "air tight" stove that should burn slowly, I thought. My fear with following your suggestion would be that with a 2" difference between the stove flue, and the chimney, they might have similar or worse draft difficulties. AM I right here? I am no expert in wood stoves or chimneys.

A lot depends upon weather the chimney is located mostly indoors or if it goes directly outdoors and up the outside wall. Which type of install do you have?

The chimney goes straight up from the stove to the ceiling using double wall black stove pipe, then connects to the metalbestos chimney which passes through a 18" high attic space and then outside. The length of chimney outside is about 10 or 11 feet, required to obtain the 10 ft unobstructed radius at the top. There is a proper rain cap to finish off the chimney. My thinking is that there is a lot of "cold" chimney which may have a detrimental effect on the draw if a 6" stove is connected to it.

My thinking is that there is a lot of "cold" chimney which may have a detrimental effect on the draw if a 6" stove is connected to it.

Your thinking is correct and there is no listed safe way to shrink up the 8 inch pipe.

As a inspector myself I have allowed the non listed wood stoves to be installed if they met the CABO code or the commercial mechanical code. We could safely certify the older stoves if they met all the conditions.

Click the link to see what I am talking about

NASD: Wood Stove Installation and Operation


You might get the insurance inspector to buyoff on this OR the local building department. I inspected for the state and local counties in this area and the same situation you are iun now came up 15 years ago in this area. It seems many people changed insurance companys to save money but then found out there wood stove would not meet the new insurance companys requirements. Many of the people applied for a woodstove permit which allowed me to go out and tell them how to fix it then once fixed I would approve the install EXACTLY as I saw it at the time of the inspection including a checklist with all the clerances and special hearth extension rugs if necessary. This way I was clear in case they decided to change back or modify my approved install. Once inspected they forwarded a copy of my approval to the insurnance company. The insurance company always accepted my approval since the unit was actually looked at by a professional.

Thanks hvac1000. Just so I am certain, the chimney must be replaced and I can't slide a liner of some sort down to make it 6". If this is the case, I, personally am not opposed as the chimney is at least 25 yrs old and it might be wise to have it replaced. It is probably OK, but why take a chance? If a liner can be used, then there would be some considerable cost savings. Can you please confirm what I believe you said above, that a liner cannot be used?
Thanks.

To the best of my knowledge there is NO factory adapter/liner that is designed to be used with Metalbestos factory designed pipe as to a method of reducing the inside diameter from 8 to 6 inches on a continuous basis for the length of the chimney. I am not saying it cannot be done but Metalbestos does not offer the item to accomplish this. Since it is a factory made assembly and UL/CSA listed as such any attachments to reduce the internal diameter would have to be made by Metalbestos to be used with that model number pipe. SO to stay within the safety code you cannot shrink it down internally.

When you start buying a new stove and a new chimney the cost gets real high. That is why I thought I would give you a heads up as to how to possibly work around the problem. If you have the cash then buy all new and install EXACTLY to the manufactures instructions. If this new system will need a inspection for your insurance company I suggest you contact the inspection official or independent inspector to see if they will need a ruff inspection of the chimney as it passes through the ceiling/roof assembly so they can check to make sure the clearance from combustibles/insulation is correct before you cover it up.

Thanks for your insight. Best course of action is to replace all of the chimney and the stove. I shall advise my friend and let them decide.
Much appreciated.