"xanuda" writes:
Hi all. We are looking to replace our old furnace. We have had a few
estimates and now we are trying to decide between an 80% and 90%
efficient heaters and 1 stage / 2 stage / variable models. The price
difference between 80% and 90% seems to be about 600-800 for Trane.
The price difference between different stages is also several hundred
$$$. How do we make a decision whether it is worth money to go with a
more expansive model. I'm looking for a dummy-oriented advice as my
knowledge here is pretty mich zero

Hey Gene,

First, I'll pull this homeowner question into alt.home.repair and set
followups to it. I suppose you'll see why soon enough when some of
the regulars go into Lord of the Flies mode. Yes, it's odd that a
clearly hvac question is not welcome in such a named group, but what
can ya do?

First, where do ya live, that helps focus how much heating this
furnace is going to be doing. How long do you plan to stay in the
home is another factor, as it determines whether the payback period
for additional efficiency will every be enjoyed by you.

The best I can divine from a variety of resources as I was through
similar decisions, 2 stage and variable speed are mostly comfort
benefits. 2 stage is relatively simple--it's just that the gas valve
has two settings. You run mostly on the lower setting until it gets
damned cold or you're trying to heat the house from a set back
temperature. This prevents the furnace from short cycling, and gives
you less dips in temperature, may prolong the life of the heat
exchanger and blower. It doesn't seem to come at much risk of adding
to maintenance later as the mechanism seems to boil down to a gas
valve that has Off, low and high settings, and some control logic that
dictates when to kick it into high.

Variable speed seems to be contentious. It too is to afford you more
comfort and better ddistribution of heating and cooling by keeping air
cirulating in the house without having to have the noise and
electricity use of running a single speed fan full bore all the time.
Whether the energy savings translates into $ savings is subject to
some debate since some point out that variable speed motors are very
expensive and have a lot more stuff to break on them, while single
speed motors have a long history and are pretty simple and relatively
inexpensive. Others say variable speed is the cat's ass and makes a
huge comfort difference. Other benefits include that you can keep
your air moving and achieve better filtration as such, and supposedly
you get some added dehumidification benefits as a variable speed's
continuous air flow will keep things less humid in the AC season as
air is circulated over the cold coil in the periodcs the A/C is off.

80 vs 90%. Take a look at your gas bills. Try to divine how much you
use each winter for heating. Figure out how long it'd take to get
your money back if your gas usage was 12% lower for the heating
portion. Also factor in that for the installation they'll need to run
some PVC pipe to vent outside out house as the 90% won't use your
existing flue, but are so efficient they vent out PVC. There is some
concern that higher efficiency furnaces are less reliable and may cost
more in repairs down the road. I haven't yet determined if that's a
real concern or not myself. Finally, take your crystal ball and
divine whether you see current natural gas prices staying relatively
flat, or increasing in the future. This also plays into the packback
scenario.

All that said, I've also been told yo're better off energy wise with a
2-stage 80% than a 1 stage 90% at least in my situation, since the 2
stage will achieve comfort perhaps at a lower thermostat setting due
to the longer cycle and better heat distribution to the extremities of
your duct system that will result.

I'm sure I managed to utter some misconception or errors in all this
info that will be mercilessly shredded by folks less interested in
helping you and more interested in being able to be right by pointing
out something that's wrong, but I hope you found some of this helpful
in figuring out what's best for your situation.

Best Regards,
--
Todd H.
http://www.toddh.net/