|
Replacing forced air gas furnace?
QUESTION:I have a home in southern California with a 1970s vintage Bryant furnace
that I'm contemplating replacing, and have some general questions.
The furnace is still working, but the blower motor is starting to get
noisy and I'm wondering if it might be better to replace it with a more
efficient and modern unit than just repair or replace the motor. While
it does an adequate job of heating and our gas bills are reasonable, I'm
somewhat concerned about possible issues with carbon monoxide from the
vintage heat exchanger as well as potential energy savings and the repair
vs. replace cost choices.
The furnace is centrally located in a closet off the hallway, and sits on
a raised floor with a hole beneath for the cold air return via a grille
under the closet door. The filter is in the bottom of the furnace, and
from looking at spec sheets I think the industry calls this an "Updraft"
configuration. Apparently the same basic furnaces can be mounted either
to blow the hot air up or down or horizontally by re-arranging some
hardware.
It's a Bryant 80-394U with a rating of 80,000 BTU input, 64000 BTU output.
I'd assume that the typical specs are for input, so this is probably what
would be termed an 80KBTU, 80% model, right?
In looking at current production gas furnaces, the typical 90 to 93 percent
efficiency units are termed "direct vent" and have two vent pipe openings,
one for combustion air in and the other for exhaust. My unit has a single
metal vent pipe, slightly oval, about 4 inches in diameter, that goes up
through a hole into the attic and out through the roof above.
If I replace it with a direct vent style, do I need another pipe for the
combustion air in? The present setup appears to draw combustion air in
from the attic via an opening about 4 by 16 inches covered with a metal
screen above the furnace. With the closet door closed the heated air for
the house doesn't appear to mix with this, as it comes up through the filter
in the raised floor and out the top of the furnace into the distribution
ducts, and I'd assume the attic opening to the closet is for combustion
air.
It would seem logical that I could use the existing vent pipe for the
exhaust vent and just leave the combustion air input pipe open to get
attic air as it apparently does now. If a second pipe is needed for
input combustion air, does it need to go through the roof or can it just
terminate open in the attic? What are the advantages of a second pipe?
Also, I've seen references to PVC vent pipe for these newer furnaces.
This seems somewhat unsafe from a temperature/fire perspective. Is there
a reason not to use metal? The roof is new this year, and I'd like to
avoid making any more holes in it.
A google search leads to a lot of manufacturers' sales literature but
not much in terms of explaining the reasoning behind the changes in
venting with the more efficient furnaces. The old furnace is 46 inches
high, 28 inches deep, and 16 1/2 inches wide. Newer units seem to be
about the same dimensions, so I'm hoping for a fairly simple swap. Is
this the type of thing outside the realm of a typical homeowner/handyman?
Should i go with a replacement 80% unit that doesn't have the two-pipe
venting requirement? I'd think that more efficient is better in terms of
energy and the environment, but we have relatively mild winters here and
perhaps the extra cost and hassle aren't worth it. I'd assume that the
builder just put in whatever was cheapest that would do an adequate job.
Would a larger BTU unit make sense?
FWIW, the house is about 1600 sf, slab floor in Santa Barbara.
ANSWER: First question is..when was it serviced last? Most times direct drives WONT
get noisy, they simply fail. Others have had different experences, but those
motors DO have oil ports, and the service guy should have been taking care
of them..altho, if the motor is of 70's vintage, its ran a good life..as has
the entire furnace...time to update. Potential energy savings? No...not potential...you WILL save money.
Also, 30 year old parts, VS new parts with warranty....go figure.. It is. Chances are, depending on your area in Southern CA, you have a slab
built home, and its normal for the combustion air to be brought in from the
attic in that case, or in more modern installations, via a section of KD
from the roof.
|
|
|
|
