Central heating downsizing, what to expect?

[stockrex]

Originally Posted By: PandaBear
Currently my house (2/F, 1500sqft, living room is what they call a "cathedral ceiling" of 2 story tall) has a 100000 btu 4 burner furnace. It would turn on for a few minutes then pause for 15-30 minutes all the time. The biggest problem however is the noise it generates by the blower pushing exhaust through a vent inside the wall between 2 rooms, waking everyone up in the middle of the night. The next biggest problem is the high natural gas bill whenever we use it.

Currently we have a 2.5 ton AC that we just installed last year and use the same furnace blower fan and it is sized just right (IMO), very quiet (the air mover is not the problem, it is the powered furnace exhaust that is loud). So if I go to a small furnace, how many BTU / burners should I look for? Does it make sense to go to 93% or higher efficiency? (I understand that we have to adjust the water condensation in the exhaust but it is right there with the AC anyways).

Should I stay with PSC fan or ECM fan?


Panda,
do you have a single stage furnace? or dual stage?
I can't imagine a 100k single stage, that is a lot of juice, plus you are in a warm zone

you can set the fan speed on the furnace it can be varied by 10% on newer furnaces.

in MI, it is -7F outside and I have a 80k btu furnace in a 2200 sqft ranch.

saying that, I don't think u need waste money in replacing the furnace, but tweak it a little.

how old is it? what brand? is the fan DC or AC?

on a side note I would install a fan on the vaulted ceiling and keep it running to mix the air, where is the thermostat located?

 

[PandaBear]

The unit is a Rheem RGDG-10NAMER, Criterion II

Made in 94.
The valve is 60-22866-01
The fan / motor is 1/2 HP, 117104-01.

Do they make multistage burner back then?

 

[IndyIan]

Roxul has a melting point of 2200F. It won't burn if its on the burner. And drywall is around $0.40/sqft. I would get a HVAC pro to give the OK to install roxul or something around the exhaust in any case.
It might be the case that the power vent fan has to be sized to the run of exhaust pipe regardless of how many btu the actual furnace is? I don't know.
I do know that I wouldn't want my 70k btu hot water tank venting through the interior walls in my house, even with its ABS pipe exhaust. Its not quiet.
If you go to the expense of a new furnace, probably you should have them reroute the exhaust more directly outside some how, while they are there.

 

[PandaBear]

Took the furnace apart to take a look and found that:

1) The filter inside is merely a plugged screen, so I washed it and will get a real filter on it soon.

2) The draft inducer motor housing is cracked, not hairline crack but about 1mm wide across 1/3 of the way. I probably will replace the motor housing / assembly and see if it help with the noise.

Are there any difference in noise level between replacement brand / model?

 

[stockrex]

Originally Posted By: PandaBear
Took the furnace apart to take a look and found that:

1) The filter inside is merely a plugged screen, so I washed it and will get a real filter on it soon.

2) The draft inducer motor housing is cracked, not hairline crack but about 1mm wide across 1/3 of the way. I probably will replace the motor housing / assembly and see if it help with the noise.

Are there any difference in noise level between replacement brand / model?


Panda,
I spoke to a buddy of mine who owns his hvac business.

Couple of points he made:
1. yes, heater is TOOOOOO big.
2. your fans CFM he guesses is like 1300 CFM,

Yikes, those screen filers don't do anything and they clog up the fan blades.

you can take the fan and housing out an wash it outside.
can you just put aluminum tape and make it work in the mean time?

tips to save money:
1. reduce the # if times the heater comes on, how about a fan in the high ceiling part? let then fan run and mix the air?

If you are going to get a new fan/motor, look into multiple speed fan that would run in 1 run when just mixing air.

muffler for air vent: I am guessing the shear speed of the air coming our sounds and/or the sound the blower is more than usual.
how about a vented 90 degree cover to quieten it down?

 

[PandaBear]

Stockrex,

Thanks for asking your friends. Yes the heater is way too big, if I were to replace it right now I'd likely get a 30000 BTU 2 stage one (Goodman has one that is 24000 BTU 1st stage and 30000 BTU 2nd stage) instead.

The air mover is actually 4 speed, and yes it is 1300 CFM, but it is actually quiet enough that is not a problem. The majority of the noise is the air rushing through the 6" vent and the inducer (both the motor whine and the air speed). I didn't thought about the 90 deg turn to insulate the sound (not sure if it will really slow it down, but it will reduce the pressure for sure), I'll research more into it.

With the temperature starting to rise this week I think I have a bit more time in looking for the fix. Home Depot here is having a $1742 installed deal for a 50000BTU 80% efficient Rheem, and I found a few places online selling Goodman 2 stage 30000 BTU 80% units for around $550 that seems to be just the right size for my places. How hard is it to replace the entire furnace yourself if the dimension is not just right? My current furnace is slightly wider and I probably have to do some sheet metal bending / adapter to the existing duct. How much is the labor if you ask someone to do this kind of work?

 

[stockrex]

Originally Posted By: PandaBear
Stockrex,

Thanks for asking your friends. Yes the heater is way too big, if I were to replace it right now I'd likely get a 30000 BTU 2 stage one (Goodman has one that is 24000 BTU 1st stage and 30000 BTU 2nd stage) instead.

The air mover is actually 4 speed, and yes it is 1300 CFM, but it is actually quiet enough that is not a problem. The majority of the noise is the air rushing through the 6" vent and the inducer (both the motor whine and the air speed). I didn't thought about the 90 deg turn to insulate the sound (not sure if it will really slow it down, but it will reduce the pressure for sure), I'll research more into it.

With the temperature starting to rise this week I think I have a bit more time in looking for the fix. Home Depot here is having a $1742 installed deal for a 50000BTU 80% efficient Rheem, and I found a few places online selling Goodman 2 stage 30000 BTU 80% units for around $550 that seems to be just the right size for my places. How hard is it to replace the entire furnace yourself if the dimension is not just right? My current furnace is slightly wider and I probably have to do some sheet metal bending / adapter to the existing duct. How much is the labor if you ask someone to do this kind of work?



Panda,
Pls don't get 80% furnace, if your current one is more than 80%,
Also, look into rebates from local utils, the $$ amount is more for more efficient models. Don't forget the fed tax credit if that is still there.

I say go for, just get the same make model but lower btu so it is a drop in,
there are guys on craigs who are qualified but do it on the side for much less.

manufac won't warranty if not install by qualifed individuals, read fine print, but you will save a boat load of cash.