Gas and Oil Home Heating Furnaces - Undersized Furnace Intake? Enlarge It?
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drbob76
01-04-03, 05:23 PM
I have a gas furnace/air conditioner to service my downstairs area. The square footage of the heated/cooled area is about 1700 square feet. The AC unit is 4 tons! The furnace is a Trane XE60. The house is on a slab so the AC ducts are routed through sofits in the ceiling area.
The flow through the ducts is pathetic.
My first thought is to enlarge the inlet to the furnace. The inlet filter is 20 x 20" but the inlet behind it is only 10 x 20 (200 sq inches). I did some measuring and I can make the inlet area about 400 sq. inches just by opening up the area where the filter is now. The fan is a squirrel-cage type fan beneat the unit. The bottom frame of the unit is only 10 inches off the deck. I have attached a picture. The burner, inlet for the furnace is on the front of the furnace (90 degress from the plane of this inlet). The inlet area is sealed from the face of the furnace.
Would it be worth a try to enlarge this inlet/filter area area by 100% (extra 200 sq inches)? If so, where can I get parts and would it need to be inspected?
We have turned the speed down on the motor. I have gotten three bids for replacing the system at around $5-6,000. Obviously it is an older furnace and will need to be replace withing a few years. THe other things that could improve the flow is to redo some of the deaheading turns that come out of the furnace. I though that I might save that for the new furnace if I could improve my flow situation
The flow through the ducts is pathetic.
My first thought is to enlarge the inlet to the furnace. The inlet filter is 20 x 20" but the inlet behind it is only 10 x 20 (200 sq inches). I did some measuring and I can make the inlet area about 400 sq. inches just by opening up the area where the filter is now. The fan is a squirrel-cage type fan beneat the unit. The bottom frame of the unit is only 10 inches off the deck. I have attached a picture. The burner, inlet for the furnace is on the front of the furnace (90 degress from the plane of this inlet). The inlet area is sealed from the face of the furnace.
Would it be worth a try to enlarge this inlet/filter area area by 100% (extra 200 sq inches)? If so, where can I get parts and would it need to be inspected?
We have turned the speed down on the motor. I have gotten three bids for replacing the system at around $5-6,000. Obviously it is an older furnace and will need to be replace withing a few years. THe other things that could improve the flow is to redo some of the deaheading turns that come out of the furnace. I though that I might save that for the new furnace if I could improve my flow situation
Ed Imeduc
01-04-03, 06:28 PM
You dont say what your ac load on the home is . 4 ton for 1700 sq on a slab,that sounds like alot to me. An old rule on the duct size is 60" to 80" per ton so your return duct should be around 320sq" tops. I would open this up for more air first and see how it helps for now. Dont know where you are or what your code is there. You should be able to do the cold air yourself. If you need more air why did you slow the blower down ???.
When you go to change get 3 bids from hvac guys and have them look at the duct work you now have and see what they say;) ED
When you go to change get 3 bids from hvac guys and have them look at the duct work you now have and see what they say;) ED