furnace fan speed

[Dutch445]

Looking at buying a house (built 2002) with a ComfortAir/ Conquest 90
75,000 BTU updraft furnace. I think it's a tad
undersized for the home, but i'm not really
an expert.
The fan seems to be very limited in airflow thru
the ducts, at least in the rooms. I will admit there
are probably too many runs on the system.
(cape cod home with 2nd floor finished into 2 bedrooms
and bathroom)
The manuals I find online may be for newer units, but
many of the similar units show multiple fan speeds for
the blower. It is only a 11x7 blower, 1/2 hp from what
I read.
I believe the fan runs at high speed for the A/C but low
speed for the furnace, is it possible to change it? most
specs show it has 3 speeds (the fan)
being a newer home, and high efficiency furnace, we may
be ok with the size, but with a little more cfm we may
be happier.
here is a document with some specs published in 2004, mine
is probably an 01 or 02 model.:

 

[murphy1244]

You need to check your difference in temp from return to outlet. You will find the spec in the book. If air speed is too high, you will have cooler air-not good. If air speed too low the temperture will cause a possible meltdown-Really not good. Most newer furnaces are 3 speed. Good luck.

 

[Car Doc]

Cant tell you on those specs but recently I put in a 5 ton package unit cooling only at my shop. I switched it from low to high just by moving one wire on the motor, all you can do is try it see what happens it cant hurt anything.

My electrician said it was on low for the heat and cool unit so the heat exchange would be better but for cooling only I could get away with it. fwtw

 

[murphy1244]

The stat you want is tempeture rise- That is the difference from incoming air and out going air. The 90plus furnaces run a tad cooler at end of cycle to get all that warm air that is normally wasted. Yes I do this for a living.Also make sure youhave a clean filter.

 

[Dutch445]

I'll speak with my gas service guy, he'll be able to
see what changes are possible without hurting
performance/economy.

my fear is it's borderline too small for the house as it
is now, but we'll see.

the other part of this is we are in the waiting game
for closing , they think mid January, and the house is
empty, so i took responsibility to have the heat on until
then so it doesn't freeze up.

 

[Fixemall]

Dutch, I would see if I could get in there and at least blow out the water lines so as to prevent a real issue, you are only a power failure away from disaster.

 

[zzvyb6]

Check to see what kind of filter you are using. Most of the new micro-particle filters reduce the air flow rate in order to get the allergens. In my case, use of these filters caused my furnace to be starved for air and it overheated, melting the thernal sensor. The furnace blower is easy to rewire so that the heat setting speeds can be changed. Believe it or not, many owners want the low speed only for noise reasons, not efficiency considerations. My new Trane (which replaced the Chernobled unit), runs the fan at a low speed for circulation reasons all the time. The result is a very uniform heat in all the house rooms and no more dust.

 

[kenmac]

Without mod # I'm just guessing. 3Ton should be 1200 CFM'S given 400 CFM per ton dirty evap./ return air filter could also hinder air flow

 

[Dutch445]

the model I have is GLUA75-E3A, 75k btu, updraft, 92.8% efficient,
that attached pdf may not be the exact year, or exact spec, but it
sure looks like what i have.

not concerned with A/C performance yet, maybe next summer that
will get used. (never had central a/c )

for this initial run, i have pulled the filters out, including the one that
had pulled thru and into the side of the fan housing. (pretty plugged)
there are 2 bedrooms/living room/2 bathrooms/kitchen/dining
rooms in the first floor. furnace was probably ok with that,
but upstairs is 2 more large bedrooms and a bathroom that added
some more runs to the system.

i am looking at adding onto the system also, currently burn coal
in a handfired stove and would like to come up with another source
for heat in the new house. being newer construction, i'm sure insulation
factor is much greater than the older house i'm in now, so i'm hoping
it's easier to heat than this larger ranch i'm in now.

 

[kenmac]

I would be concerned that the evap. coil would have some blockage given the lack of maint. (filters stopped up,).There could also be a good amount of dust/dirt within the duct work. If the unit isn't performing well in heat mode, It's not likely to perform well when you are ready for A/C. I assume It's an up flow furnace & you are calling it an updraft furnace. I would suspect it maybe too small . If were sized for the home & later, the home was added to. The 3 in the mod # would indicate 3 Ton. I would have an HVAC company to check the unit B-4 purchasing. Unless you'er getting a deal & don't mind paying the cost to upgrade the system if needed. I don't know how the house is built but, you may be able to add a seprate system for the upstairs . Just a thought