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mjimenez 10-25-2011 08:06 PM

gas furnace replacement
 
Hi all,

My furnace a Coleman 2632 Series 756 105k input 84k output, gave out this past Sunday. It is the original furnace in a 1958 1 1/2 story 1250 square feet wood shingle Cape very poorly insulated with original insulation located in Connecticut . Well needless to say need to install a new furnace asap.
The problem: Ductwork size is 3 1/2 inches pipes, talk about static pressure.
Walls are 2 by 4 stick construction 3/8 inch Sheetrock

Currently considering the following furnace
Ducane 80G1UH090BP12
88,000 BTU Furnace, 80% Efficiency, Single-Stage Burner, 1,200 CFM Multi-Speed Blower, Upflow / Horizontal Flow Application 70400 output

Strapped for cash I plan to DIY this venture put will hire Plumber and electrician for final expectation before firing it up. Any and all suggestion are welcome. Winter is fast approaching thank you in advance for your help.:icon_confused:

Marty S. 10-25-2011 08:54 PM

Seal and insulate first then find out what size furnace is correct for your house. Duct is going to be an issue that will need addressed,plan on all new or buy a mobile home furnace that's designed for high static. Sounds like a major DIY project with not much time before the cold comes. Good luck.

PS. Check the warranty out from the mfr. since there may be none with a web buy and DIY install.

mjimenez 10-25-2011 09:12 PM

Thank you so much for such a quick response . An on line dealer recommended a mobile furnace I will look further into this suggestion.

Marty S. 10-25-2011 09:25 PM

Don't forget the important first step-seal and insulate. Probably only need a 50K or less furnace once done which makes the pay back quick.

beenthere 10-26-2011 04:20 AM

Mobil home furnaces don't have ducted returns. Does your current furnace have a ducted return?

Mobil home furnaces don't really move much air against high static, its a myth that they do.

By insulating your home first, you may bring down the size of your furnace enough that the current supplies are enough to use.

JackDidley 10-26-2011 08:29 AM

Quote:

Originally Posted by beenthere (Post 756916)
Mobil home furnaces don't have ducted returns.

Can you explain this ? Ive never looked at a mobil home furnace. How do they get return air ?

mjimenez 10-26-2011 09:04 AM

Thank you both for your input, although I must admit I am a bit more confused as far as using a mobile home furnace in this application. The furnance suggested by the online dealer is the Alpine AHMG9S080C16MP popular
80,000 BTU Mobile Home Furnace, 95.5% Efficiency, 1,600 CFM Multi-Speed Blower, Upflow / Downflow Application. If I would side vent the intake and exhaust would this eliminate the return issue and improve the static pressure issue.


Thank you

bungalow_steve 10-26-2011 10:13 AM

Quote:

Originally Posted by mjimenez (Post 756718)
Hi all,

My furnace a Coleman 2632 Series 756 105k input 84k output, gave out this past Sunday. It is the original furnace in a 1958 1 1/2 story 1250 square feet wood shingle Cape very poorly insulated with original insulation located in Connecticut . Well needless to say need to install a new furnace asap.
The problem: Ductwork size is 3 1/2 inches pipes, talk about static pressure.
.:icon_confused:

All the ductwork is 3 1/2 inches? What is the size of the main trunk coming out of the plenum? How many 3 1/2 branches coming out? You can add ductwork off the main trunk while leaving the existing intact (hard to get at ductwork I assume) to reduce static pressure, this is what is normally done and you can do it fairly easily.

bungalow_steve 10-26-2011 10:15 AM

Quote:

Originally Posted by mjimenez (Post 757027)
Thank you both for your input, although I must admit I am a bit more confused as far as using a mobile home furnace in this application. The furnance suggested by the online dealer is the Alpine AHMG9S080C16MP popular
80,000 BTU Mobile Home Furnace, 95.5% Efficiency, 1,600 CFM Multi-Speed Blower, Upflow / Downflow Application. If I would side vent the intake and exhaust would this eliminate the return issue and improve the static pressure issue.


Thank you

No it would not.

mjimenez 10-26-2011 11:45 AM

The 3 1/2 inch pipes come right of the plenum, there are 7 of them.

mjimenez 10-26-2011 11:46 AM

no trunk

bungalow_steve 10-26-2011 12:00 PM

Quote:

Originally Posted by mjimenez (Post 757144)
The 3 1/2 inch pipes come right of the plenum, there are 7 of them.

Yea, that is not even 200cfm. The mobile furnaces have the same standard motor/blower as regular furnaces, the opened return (no ductwork) is what helps them drive the airflow (they don't have to deal with both sucking in the air through return ducts and pushing air through supply ducts).

If you install a mobile furnace in your home it will suck in air from the hot water heater vent, and whatever else is in the area, so I don't recommended it. It's not code either, inspection will fail, warrenty will be void, home insurance claims will be denied etc etc.

beenthere 10-26-2011 03:32 PM

Post pics of your current furnace and duct work. I'm pretty sure I know what furnace you have. And if a properly sized furnace is installed, often there are no problems.

Coleman had 2 versions of the furnace that used small ducts. I believe the 3.5" ducted one also used a relief register in the plenum.

beenthere 10-26-2011 03:35 PM

1 Attachment(s)
Mobil home furnaces have their return come in the front of them through a louvered door.

hvac5646 10-26-2011 04:47 PM

Have any of you guys given any thought as to how a Mobile home unit vents?

The standard model use a direct vent concentric with a speciality termination \.

They are not meant be vented higher than the mobile homes roof line.

Point being: You cant vent a mobile home furnace up the longer flue of a residential flue.
Also it is against the law to put a MB furnace in a residential home.

Says so right in the instructions and NFSC.

As far as the argument of hi-static blowers go; it is inexpensive to just up size the 31/2" ducts to six inch and have them come off the plenum of the new furnace (I would make the plenum larger then the furnace opening by two inches on both sides of the plenum frontal dimension). I for one use Nordyne furnace which have high static blowers and I do gain extra cfm since in most cases I am installing the RIGHT size because the old one was over size.

For what it cost to buy a 80% furnace i think you should pop for a 90% (I would suggest a 60KBtu or 72KBTU 95% NORDYNE)

Here in MI a 80 furnace sells for about $600 and a 90% is around 800 bucks.
This approach I have outlines is the least costly route you can take be taken.
Hope this helps.


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