Proper duct sizing
#1
04-04-15, 03:11 AM
Proper duct sizing
My law enforcement, retired friend wants to add air to his existing system. Two different estimates has him wondering, 1700 sq ft raised ranch.
1) put A coil on top of furnace in basement and use existing 4 inch ducts
Or 2) put unit in attic and re-duct down from there with 6 inch ducts.
Also not sure which is proper size condenser?
One contractor says you can't push enough air thru 4" the other says no problem? He doesn't know who to believe.
Your thoughts welcomed, thks.
1) put A coil on top of furnace in basement and use existing 4 inch ducts
Or 2) put unit in attic and re-duct down from there with 6 inch ducts.
Also not sure which is proper size condenser?
One contractor says you can't push enough air thru 4" the other says no problem? He doesn't know who to believe.
Your thoughts welcomed, thks.
#2
04-04-15, 09:30 AM
Group Moderator
I have a furnace in the basement that I added an A coil to. The system performs well on the first floor but the second floor is an issue.
It's hard to get an efficient system using a furnace since the ducts are low on the wall or in the floor. Cold air doesn't rise and just settles at the floor.
I don't like putting an air handler in a hot attic but in your case it would make the most sense.
It's hard to get an efficient system using a furnace since the ducts are low on the wall or in the floor. Cold air doesn't rise and just settles at the floor.
I don't like putting an air handler in a hot attic but in your case it would make the most sense.
#3
04-04-15, 10:24 AM
Join Date: Mar 2006
Location: Wet side of Washington state.
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Unless your friend has many four-inch ducts coming from a large trunk duct the four inch is too small for heating much less for cooling. Since the temperature differential is less for cooling there must be greater airflow and that requires larger ducts. I would not even think about calling back the salesman that recommended the four inch ducts could be used.
Condenser size must match the evaporator size and that is dictated by the amount of cooling in BTUs per hour is required. A Manual J (manual as in book) calculation for heat gain is necessary to determine the amount of cooling required.
Condenser size must match the evaporator size and that is dictated by the amount of cooling in BTUs per hour is required. A Manual J (manual as in book) calculation for heat gain is necessary to determine the amount of cooling required.
#4
04-05-15, 07:13 AM
thanks, is it reasonable for them to consider adding additional 6 inch ducts to supplement the 4 inch, just so they don't have to rip out/change everything?
