Furnace placement – attic or crawlspace
debden
| Posted in Energy, Heating & Insulation on
Help! We bought a new house and are replacing an old oil heater with a gas furnace. Existing furnace is in the crawl space with all duct work in crawlspace. Currently we can’t fit a new furnace through crawl space opening so it would require cutting a hole in the floor to get a new one in (and old out). One HVAC contractor is recommending adding New furnace to the attic and running a duct down from new furnace to original ductwork in the crawl space. We would be adding one new duct and vent in a room that was added to house and that ductwork would run through the attic. The attic certainly seems easier as we have a large easily accessible attic but would love any thoughts on this arrangement and suggested placement.
Replies
Your A/C will also be up in the attic. You're going to need a condensate line for both the A/C and the high efficiency (condensing) furnace. Hope a condensate line doesn't get blocked. You'll therefore need a pan below the furnace with a float alarm to warn if the there's a leak. Depending upon where you live, you're going to need a humidifier up there also. Do you really want one of those with their cheap saddle valves and float valves above a finished ceiling in your home (even with the aforementioned pan)? How do you easily prevent that water supply line from freezing up in the attic during the winter? ...not to mention going up to the attic to clean the humidifier each spring. ...and install furnace filters a few times each year.
I also think that the whole thing is going to be less efficient. You can insulate the ducts but what about the furnace itself. The air that flows through the furnace will be subjected to the extremes in both the summer and winter.
Me? I'd make the the hole in the crawlspace bigger.
Our attics here in Canada are pretty nasty with insulation and the trusses. --and have to be careful where you put your foot so that you won't go through the ceiling. You, on the other hand, might have insulation and the vapour barrier between the rafters of the roof and a wood floor in the attic. ...and then again I've seen some pretty nasty crawl spaces.
Just my 2 cents.
What size is the main ducts on the existing furnace?
If attic installed, both the supply and return ducts will need to be connected.
Do you have space available for that?
I vote for making access to that crawlspace, and replacing in-kind.
run heating for the addition under as well.
perhaps you can rig up an Addams Family style access under the stairway, or perhaps a Munsters style trap door.
Do you have a closet that would present a good location for a trap door? Remember you will need to provide for continued access for service as well as eventual replacement.
How did the crawl space access get plugged up in the first place?
If the HVAC system will be located in an encapsulated crawl space what size foundation wall access opening is recommended?
R408.4 Access.
Access shall be provided to all under-floor spaces. Access openings through the floor shall be a minimum of 18 inches by 24 inches (457 mm by 610 mm). Openings through a perimeter wall shall be not less than 16 inches by 24 inches (407 mm by 610 mm). Where any portion of the through-wall access is below grade, an areaway not less than 16 inches by 24 inches (407 mm by 610 mm) shall be provided. The bottom of the areaway shall be below the threshold of the access opening. Through wall access openings shall not be located under a door to the residence. See Section M1305.1.4 for access requirements where mechanical equipment is located under floors.
Planning ahead, you also need to make the opening, immediate area outside, and the path from the opening to equipment location large enough to allow equipment to be moved in, installed, serviced, and replaced.