replacement flue liner options

lemesi

We recently bought my grandparents' house so now we're getting caught up on a number of maintenance items and upgrades. As part of this, I had the chimney cleaned and inspected. This probably hadn't been done in decades as the fireplace has almost never been used in my understanding (though we do want to use it next year).

We have two rectangular flues with tiles (11"x7" inner dimensions, I think). I'd guess the total chimney height is about 25' (back of the envelope calculations for single story + attic + basement). We have a Weil-McLain WGO-3 oil boiler (115,000 BTU), with a 7-inch pipe coming out of it and I guess what you'd call a barometric damper. Our attic is not insulated.

The inspector determined that, due to deterioration, we need a new liner just for the boiler flue. His quote is for a 6" hybrid smooth wall liner.

I ultimately decided I didn't really like that guy much because he didn't really want to answer my questions. Therefore, I also had a second company come out to confirm the diagnosis and give a quote. This guy was very willing to discuss options. He says that code doesn't normally allow him to reduce the size of the pipe coming out of the boiler (7") and this presents a problem because he won't be able to fit a 7" liner within our current tile liner. This will necessitate removing all of the existing tile. Even worse, we have no gap between our flues, so he will also have to remove all of the tiles in the fireplace flue and replace that as well. He says doing this will allow him to run two new flue liners, a 7" round one for the boiler and I think he said an oval one for the fireplace. He showed me two options for the liners themselves, both flexible but one with a smoother inside (I think maybe this is the "hybrid" liner the first guy referred to).

The second guy presented another option as well. He says that the 6" round liner actually drafts better than the existing rectangular liner I have currently. So he says if I can convince the building inspector to allow it, then he is happy to go that route.

So I have questions:
1) Will my Weil-McLain WGO-3 oil boiler be fine with a 6" flue liner? Is this truly a better draft than the rectangular liner I currently have?
2) Is it true that code doesn't allow downsizing the pipe coming out of the boiler? Is it realistic to get an inspector to allow it otherwise?
3) Are you familiar with this smoother-walled option? Is that the same thing as "hybrid?"
4) Would I benefit from an insulated liner, since it passes through my uninsulated attic?

My goal is first and foremost to optimize the safety and efficiency of the boiler. Price is a secondary consideration, but obviously I want to be smart about things. Given those goals, do you have any other thoughts on how to do this project properly?

EdTheHeaterMan

5" is fine for that boiler

The reason the opening is 7" is because Weil McLain only makes one rear section for that GO series boiler. 7" is required for the GO-9 boilers, You can use 5" on a WGO-3 boiler. Says so on page 16 of the installation manual.

Bob Harper

The liner can be smaller than the connector and should be sized to the boiler's input rating and per mfr instructions. The connector should remain the same diameter as the appliance flue collar right to the liner then neck it down at the wall to attach to the liner. No galvanized steel connector permanently cemented in the wall-ss only. Try to get the maximum vent rise you can while maintaining clearances to combustibles.

lemesi

@EdTheHeaterMan What are Minimum Breeching Diameter and Minimum AHRI Chimney Size? I'm not familiar with those terms.

EdTheHeaterMan

"Breaching" is the term for the exhaust opening of a boiler or furnace. Minimum AHRI chimney size is determined by members of an organization known as the Air conditioning Heating and Refrigeration Institute (AHRI). They're the people who determine the standards in the boiler industry.

Since you have a 25 ft chimney, you exceed the minimum requirement of 15 ft The 5" diameter is the minimum size you can connect to the back of the heater (so a 7" x 5" reducer fitting may be used there). as far as the 8 x 8 rectangular or 6" diameter, you should be able to fit that 6" liner inside your existing tile liner.

No need for special approval, the numbers are already approved by the manufacturer's specifications. Include this information with your permit application.

Mr.Ed

PS.
Depending on the inspector and his understanding of how chimneys actually work, you may be able to use a 7" pipe to the liner and reduce to 6"... or you may need to reduce from 7" at the boiler opening to 5" as indicated by the manufacturer instruction. Then increase to 6" at the liner connection. Both ways are acceptable. I believe the 7" connector to the 6" liner is preferred because you can install a 7" barometric regulator. That will offer you more control over changing draft conditions of the chimney.

A 5" connector can only accommodate a 6" barometric regulator... but the 5" connector will also restrict the flue gas flow inside the heat exchanger allowing for more heat transfer into the boiler water. That is a good thing... that is why both are acceptable.

lemesi

So I'm happy to see that a 6" liner seems fine. That will save me a lot of money and trouble. Any input on the other questions?

3) Are you familiar with this smoother-walled option? Is that the same thing as "hybrid?"
4) Would I benefit from an insulated liner, since it passes through my uninsulated attic?