chimney liner

Paul S_3

I have to run a chimney liner on a boiler replacement ...the customer is telling me it has to be stainless. Its for a atmospheric cast iron boiler....does it have to be stainless....last boiler failed due to low return water and oversized flue...there was major signs of condensation

Ironman

Doesn't HAVE to be unless the local jurisdiction requires it, but it's prudent to do it that way. The aluminum ones have been known to have premature failures.

If it's on an outside wall, then it needs to be insulated also.

A power venter is another option.

This is why I lean heavily toward mod/cons. Once you've factored everything in like this, it's not much more in cost and may be less in labor. But if you go this route, don't leave the existing gas water heater orphaned on the old chimney.

SWEI

Ironman said:

This is why I lean heavily toward mod/cons. Once you've factored everything in like this, it's not much more in cost and may be less in labor. But if you go this route, don't leave the existing gas water heater orphaned on the old chimney.

Completely agreed. The last three jobs where we've priced it out, the mod/con plus PP flex vent minus the utility rebate have made the decision a no-brainer.

Jack M

Paul S said:

...over sized flue..... major signs of condensation

Did the condensation rot out the boiler? How "oversized" was it? I would be looking for other sources contributing to moisture in the flue. A failed chimney cap? Another appliance sharing the flue? Poor draft control? Is the smoke pipe so long that the flue temps are dropping before they reach the chimney? Is the mortar/masonry sound in the existing unlined chimney? What signs point to the flue as a contributing cause with the moisture issue? Could a leak in the boiler have been sending water up the chimney and creating the low water issue? Older or low efficiency boilers sometimes send so much waste heat up the chimney that they compensate for an improperly sized flue.

Paul S_3

gas fired atmospheric 165 input.... flue is square 10 x 10...only appliance on chimney

Robert O'Connor_12

Why can't a loop/bypass be installed to protect the boiler from cold return temps?
If it's a cold exterior oversized chimney then a liner is right way to go.
The chimney is over 3&1/2 x's the size of flue. Not terrible, but not great either.
Go correct size Stainless.

Robert O'Connor/NJ

ChrisJ

How about an insulated SS liner?
Seems like it'd be the smart move to me in such an oversized flue.

Paul S_3

Would just a simple bypass protect the boiler at all times ....its all in floor radiant

Jack M

Paul S said:

....last boiler failed due to an.. oversized flue...there was major signs of condensation

I'm not following how condensation in the flue led to the boiler's failure, but that aside from what I have read, the liner chosen (it can be any one) has to meet the requirements of UL Standard 1777 "Chimney Liners" and be listed and labeled.
UL 1777 is a performance standard, it does not specify a material or particular approach. Manufacturers are free to use virtually any design (aluminum, steel, tin cans) provided that they pass tests in the standard. For this reason it's difficult to answer generalities like " does it have to be stainless?".
The label stamp on the liner will specify whether the liner is suitable for Category 1 gas- or propane fired appliances, for oil-fired appliances, or solid fuel appliances. The manufacturer may make other recommendations such as the venting of coal-fired appliances.
And with respect to insulating the liner; the only circumstances in which insulation is not required is if the clearances of the existing chimney comply with the requirements of NFPA211 or the building codes enforced locally. But the majority of masonry chimneys do not have sufficient clearance to combustible materials and the effort required to thoroughly inspect a masonry chimney to confirm clearances can be a difficult and time consuming. Given all this, its easier to assume that insulation is required around the liner.
Even if clearances comply with the code there are good reasons to insulate.

Rrey

I think the failure was more due to cold return water keeping the castings cool causing condensation inside the boiler. I agree with the bypass to allow the boiler to reach and maintain temperature high enough to prevent it.

Rrey

And my a low limit circle control for good measure

Jason_13

My lining guy physically pointed out in the NFGC that any boiler efficiency less than 84% can be aluminum but 84% and higher must be stainless. Happened a few years ago.