On Fri, 19 Oct 2007 09:55:04 -0700, wrote:


As for the water heater, I don't know what kind it is. I don't think
you can vent it through the same PVC, even if it's a power-vent type, and
if it's an ordinary heater it will need to use the chimney, not PVC.
Is the contractor you are using, who recommended the liner, the one
you "trust the most", as mentioned below?

Should the high efficiency furnace be installed then the PVC pipe
intake and exhaust for this furnace must be entirely separate runs and
nowhere near the hot metal flues. I am convinced about the high
efficiency claim because the waste gas coming out at the furnace
plenum is cool enough to put one's hands around them. In the old
style furnaces that will be too hot to touch and that's waste heat
going up the flue. In fact keep the PVC piping as far away from the
current exhaust's stack on the roof to avoid the PVC intake sucking in
poisonous exhaust gasses. My preference will be to run the PVC
through a side wall to reduce the run length and the convenience of
just making two holes through the floor joist instead of running them
through the first floor, the ceiling and roof. And I will have to do
this in a way that the PVC pipes won't intrude into the decor of the
house insides, keep a respectable distance from the hot water exhaust
flue........ too much of a hassle all round.

My hot water heater's 4 inch flue is connected into the main 6 1/2
inch flue for the furnace. This is made of galvanized steel sheet and
too hot to touch when the burners fire up. The now disconnected
from the old "no longer there" furnace 6 1/2 inch flue will certainly
be too large to vent just the heater waste. It will likely risk
having hot water heater exhaust gas blown back into the basement (or
the rising hot exhaust may drive a convection current up the flue thus
drawing useful heated air from the basement??). The installation
manual recommendation is to run the 4 inch flue all the way up through
the roof as a liner inside the 6 1/2 inch pipe. That way you don't
need to do any major work cutting through though the ceiling, roof,
flashing, etc. You cannot run the PVC piping up the same 6 1/2 flue
as the hot 4 inch flue will melt the PVC pipe. I have a high and very
steep roof and the run is equivalent to two floor lengths. It worth
to me the $250 asked for the labor and materials. The material cost
is minimal. The other contractors may have included this in their
quote without identifying it as a separate item. This modification
should be mandatory. It would be a negligent for a installer to omit
it and force the homeowner to correect the omission at a later date.

As for BTU calculations it takes only a grade 8 qualification to enter
a Trade Apprenticeship program. Doing math is not a strong skill. I
can understand their reluctance to provide the math. The current
furnace should give a strong feel as to whether its undersized or
oversized. Go from there.