I will soon be moving in to a new (to me) house, and I have been advised
that the existing furnace and heat pump are at the end of their useful
lives. The house was built in 1971 and the natural gas furnace appears
to be original to the house; the outside electric heat pump unit dates
to the early 1980s and may have been the first A/C that the house had.
The home inspector said that the heat exchanger in the furnace has rust
holes in it, which is allowing combustion gases to leak into the house.
The heat pump didn't have any obvious problems, but he said a 20-25 year
lifetime was about right for this area. So it looks like I get to buy
a furnace and A/C.
The existing furnace is a Lennox G8D1-82C forced air gas furnace, and
the A/C is a Carrier 38QB036300 air-to-air heat pump. It is set up as a
heat pump - for heating, if it's not too cold outside, it tries to run
the compressor first before firing up the gas. (I didn't even know you
could do that with a gas furnace, but apparently you can.)
The house is two stories total, with a basement (~50% garage, the rest
of it two finished rooms plus the laundry and mechanical area) and a
first floor (kitchen, dining, bedrooms, etc.) The basement is poured
concrete and the first floor is wood frame with full brick veneer. It
has a hip roof with regular composition shingles. The total floor area
of the house is about 1400 square feet and the house is in the Kansas
City, Missouri metro area. According to fedstats.gov, over 1961-1990,
there were about 5400 heating degree days and 1300 cooling degree days
at this location.
The entry-level replacement is probably an 80% efficient forced-air gas
furnace and a 13 SEER electric A/C. Since I currently plan to be in
this house for several years, it might pay to go for a 95% furnace and a
more efficient electric A/C. Approximately what kind of a price premium
am I looking at for 95% vs 80%? Is there a rule of thumb for what the
payback period is? (The local gas company says gas is $1.09 for 100,000
Btu as of the first of February, but I don't know if that includes all
the fees and taxes.)
Right now, the furnace and gas hot water heater share a metal vent that
goes all the way up through the first floor to the roof. I understand
that the 95% furnaces can use plastic vents because their exhaust is not
as hot. Could a 95% furnace still be plumbed into the shared metal
vent, or does it need its own vent?
I am not sure how much I like the idea of a heat pump. I guess they
work well in places further south where you don't need that much
heating, and running your A/C backwards for a few weeks a year is
simpler and cheaper than installing some kind of burner in your system.
But in Kansas City I wonder if it's a net win to just fire up the gas
right away when you need heat. Any ideas? Are gas furnace + electric
A/C heat pump systems still available?
The furnace was originally installed in an unfinished area of the
basement, with its back to the partition wall between the basement and
the garage. The return air comes in the side, near the bottom, and the
heated/cooled air comes out of the top. Sometime later, more of the
basement was finished, and the wall of the newly-finished part comes
kind of close (maybe within 1.5 or 2 feet) to the front of the furnace.
I can squeeze in there but not everyone could; I was advised that there
is supposed to be more clear space in front of the furnace for
servicing. If the new furnace could be turned 90 degrees relative to
the current one, there would be bunches of room in front of the furnace,
but I have the (possibly incorrect) idea that it's easier to turn one of
these kinds of furnaces 180 degrees than it is to turn it 90 degrees.
Is this true or am I confused?
If turning it 180 degrees is easier, I would need to cut a doorway into
the garage; this is a non-load-bearing wall so that's not a very big
deal. I figure I would take out at least two studs and cut the drywall
back to make a four-foot-wide hole, let the HVAC guy do his thing, then
frame it back to some reasonable door width and fix the drywall. Since
it goes in the garage wall, I know this has to be a one hour fire rated
door, without any vents in it. Any obvious flaws in this plan?
As far as sizing the system goes, there are lots of houses like mine in
this area, so "same as next door" might not be a totally bad idea. On
the other hand, paying a few more bucks to get it sized correctly now
might save me a lot of money later - gas and electricity don't appear to
be getting cheaper with time. Is it worth asking the installer to do a
full heat load calculation for the house?
My plan right now is to call a Trane dealer, a Lennox dealer, and a
Carrier dealer and get a bid from each one. These seem to be the
"big names", and I've lived in houses with all three brands and had
reasonable luck. (Although I think Carrier selling furnaces is a semi-
recent development; for a while I thought they just sold A/C systems
that were added on to other people's furnaces. I could be wrong.) I
will give each one of them all of the information above, plus they will
be able to wander around the house and see the current setup in person.
Is there anything in particular I should ask the guy, or look for, when
All three brands seem to have some kind of "premium super ultra nifty"
rating for some of their dealers; is there any benefit to calling one
of these dealers vs. one without such a rating?
One thing in my favor is that the house is currently vacant and my move-
in date is a little flexible. I don't want to wait a month to get the
new stuff installed, but I'm also not needing a new furnace RIGHT NOW at
10 PM on Sunday. :)
Thanks for your help!