Hot air Furnace replacement

[xman23]

I'm getting quotes to replace my hot air furnace. To qualify for a gas company $500 energy savings rebate, I need to use a 92% AFLU rated unit. With these type units they use a PVC vent, as they have condensing exhaust. I have a 6X6 masonry chimney. It has the existing gas hot water heater and the existing furnace going into it. So why can't that be reused?

 

[semipro]

Doesn't that type of unit require both an outside air intake and exhaust like below?

If so, you'd want them to be a the same atmospheric pressure, that is, exiting your house at the same location.
Don't see how you could do that with a masonry chimney.
I believe also that you're allowed only one device per flue per current building codes.

 

[heat seeker]

Maybe you'd get a lot of condensation in the flue?

 

[Dave A.]

My understanding is the exhaust from high efficiency condensing furnaces will erode a clay lined masonry chimney from it's high acid content.

 

[yooperdave]

By dumping the exhaust from a high efficiency furnace into a masonry chimney, you would have to ensure that there is enough heat in the exhaust to vent up and out of the chimney. This is not the case of high efficiency furnaces. The exhaust is also laden with moisture, another no no for the masonry chimney.
Stick to the plan and use the PVC that is required...no short-cuts!
And by rights, the water heater that vents into the 6 x 6 chimney by itself does not does not create enough heat to vent properly all the time...(specifically, while only on pilot). You will eventually see your chimney deteriorate.

 

[xman23]

Researching it , it's become clearer to me why the PVC. I believe some or all off these furnaces have a blower on the exhaust. They even require a pitched flue pipe and water drain on the flue. Thanks for the information, your right on the money.