Do I need a Chimney Liner....

[Warstud]

A guy from a local HVAC company came out today to give me a quote on a new furnace. He also figured in a chimney liner into the final cost. I questioned him about the liner and why it was necessary when the furnace vents out the back of the house thru a PVC pipe. He says because the water heater vents thru the chimney and when the inspector comes out to look at the furnace install he'll make them install the liner...due to code.
Does this sound right?

 

[earlyre]

no, but yes.

 

[simple_gifts]

I suspect yes, since the furnace "could" vent into the flue. Around here there is (1) appliance per flue; if it is occupied by the HWH, not sure how the furnace could be ducted there too.

I had chimney work done and the guy lined it with a stainless pipe, backfilling the area around it with heat resistant insulation. This was a UL approved device he said was required since my floor joists actually touch the brick chimney and there is no ceramic tiling inside.

 

[MrHorspwer]

Your installer is correct.

An old standard, low effiency furnace (68-72% AFUE) wastes a lot of heat going out the chimney. This heat tends to keep moisture levels in the flue low.

Stepping up to a mid-effiency system (80-83% AFUE) doesn't waste near as much heat out the chimney. This allows moisture to form in the flue and will combine with the waste combusion gases to create acidic condensation that will destroy an existing masonry flue liner. A new liner is needed to prevent this.

Your new high effiency furnace (92%+ AFUE) vents out the side of the house in a PVC pipe. The only combustion gasses exiting through the chimney will be that of your water heater. Most chimney are naturally drafting. They are sized based on the amount of combustion gasses expected to be flowing through them. When you take away the furnace, not only are you taking away the heat like the mid-effiency unit, introducing a moisture concern, but you are also venting that little water heater into a chimney that is much, much too large. So large that it may lose some of it's natural draft and not be able to fully exhuast the combustion gasses. The flue liner will be sized accordingly, much smaller than your current flue, keeping the natural draft of the chimney.

Some reading:
http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12530

 

[MONKEYMAN]

When they installed furnace that vents out the house they were supposed to install a flu liner. They failed to do that, and the hot water heater would not vent properly. Flu liner installed and problem was solved. It was $500 for a contractor to install. Hot water heater was replaced and everything needed to be set to code.