Chimney Liner question.

misterheat

We recently realized we didnt have a lined chimney. We have had a gas boiler with steam heat for years. We are getting liner installed this week . Will there be any noticable differences? Its an IN 5 . What happens to an unlined chimney that has a gas furnace exhausting in to it? TIA

Bob Harper

Chimneys have required liners since 1927. The liner is there to protect the surrounding masonry from the attack by the acids in the condensate of combustion by-products and to contain the heat & flue gases. The size of the flue must be appropriate for the class of service. When sizing corrugated stainless steel liners, be sure your contractor derated it as specified in the code. Corrugated liners get derated 20% right off the bat plus additional derating for offsets. However, a recent improvement is the smooth wall liner that does not require derating. It is more expensive but, in my book worth it. A lot is made about insulating liners. It is required for solid fuel applications only to meet the listing. If you seal the top support plate and base and the chimney doesn't leak like a sieve, you have air insulated it. I recommend getting a liner with a transferrable lifetime warranty. If you are common venting a fan assisted appliance or oil, I recommend incorporating a tee as a condensate trap. Otherwise, you are allowed to sweep it in or do a "pull-through". Most liners these days are 316Ti for gas or oil but AL29-4c is recommended for highly corrosive environments. The chimney should have a level II inspection prior to relining, which includes video scanning. If the chimney is rotten with gaps between masonry units or you do not have the requisite 4" of "solid masonry units" then you have to rebuild the chimney. Liners are only listed if you have the nominal 4" solid wythe. I recommend this work to a chimney pro as he should be up on all this and have the equipment to do it properly and hold the relevant certifications and be insured for it. HTH

Jack

Bob, who is making a SS pipe in sections that can be installed? Flex is great in a difficult chimney. I have always been surprised how many offset chimneys there are. In a straight flue I like a smooth walled liner. I agree that a Certified Chimney Sweep is best for this work.

JUGHNE

If a straight chimney, is it better and more economical to lower B vent down??

D107

@Bob Harper If a corrugated liner is de-rated 20%, does that mean that if the boiler manufacturer requires a 4-inch liner, a 5-inch corrugated liner will have to be put in? (which would actually be 25% larger, or 5% larger than the 20% de-rating.)

misterheat

Will there be any noticable difference in efficiency of the boiler with the liner as apposed to without?

Jamie Hall

misterheat said:

Will there be any noticable difference in efficiency of the boiler with the liner as apposed to without?

No. Not if there is still adequate draught and the tech. setting the boiler up does it properly.

Bob Harper

To de-rate you have to look at the input BTU/hr rating in the code sizing charts. You find you common vent total under a liner diameter. Calculate 80% of that value then see if that size liner will still work. If not, you'll have two choices: go with the next size up or use a smooth wall liner that does not require de-rating. Now, just understand those values in the codes are calculations-not actual readings for that condition. I've never met an appliance that could read a chart to know whether it should work or not. The most important thing is if it works or not. To know that you must test.

Jack

Over the years representing, Dura-Vent, Selkirk, Z-Flex I would frequently hear, “I wanted to make sure I had plenty of draft, so I went the next size up.” Frequently, the next size down would have been correct. Never the larger.