Air handler issue
I have a 3 story cape code house that has the air handlers for the air conditioning system installed in the 3 foor knee wall unconditioned space. This set up has caused me a lot of problems with insulation and leaks over the years and I understand the many problems with this set up. The sysem is almost 25 years old and is nearing its life expectancy. The HVAC contractor told us that air handlers have not changed much in design or size since we installed this system and had no other suggestions for moving the system.. My questions are the following:
1. Do I have any other options than keeping the air handlers in the 3rd floor knee wall space? I do have a flat roof area over an addition that I added many years ago but it is one level lower than the existing 3rd floor units and a bit removed thereby requiring a lot of new duct work.
2. Is it true that air handler technology and size has not changed much in the last 25 years?
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Replies
Tim,
I tend to agree -- an air handler is an air handler. Blower motors have improved, however -- choose an ECM blower if you have an option.
If you can't move your air handler, consider bringing the air handler inside the home's thermal envelope by installing spray polyurethane foam in the rafters above the air handler.
Martin
Your answer brings me to my other dilema. The house was built in 1920 and the attic is really a hodgepog of ventilated design and unventilated design. It has 3 doormers in the front and an addition off of the back occupying about 40% of the length of the original house. The soffit has ventilation openings only in one corner in the back. There are no soffit vents in the front of the house and obviously none at the area where the addition was added in the back. There is no ridge vent although I stupidly added 2 attic fans vented through the roof many years ago that do not even work.
The attic floor, reached from the 3rd floor ceiling hatch, orignally had blown cellulose in the stud bays covered by fiberglass batts without air sealing. I removed the fiberglass and added 6 inches of poy iso board over the cellulose and sealed the poly iso boards with acoustical caulk, spray foam and all weather tape. The attic floor is now insulated and air sealed about as well as is possible- a tremendous amount of work. I am just now about to start on the knee wall areas in the back and the eaves in the front. Two big problems are readily apparent
Firstly, the slant area between the knee walls and the attic floor are not all accessible. There is a board running between the rafters in many of the bays at the attic floor level making them unaccessible from the attic floor. The slant bays are open at the knee wall end and currently are about 75% filled with blown cellulose without baffles. The rafter bays over the air handlers have no insulation at all and the eaves distal to the roof shealthing above the air handlers have had some cellulose blown into them.
My first dilema is do I think of this set up as being a ventilated or unventilated roof. It seems to me that it is basically unventilated since the soffit is not ventilated and no ridge vent exists. If I redo the soffit and add a ridge vent I still have to deal with the slant area between the attic floor and the knee wall which cannot be reached thereby making a true vent no practical. Should I just forget about the soffit and ridge venting and simply spray foam the knee wall ceiling rafters and fill the eaves with whatever and consider that I have to live with an unvented roof sheathing. I have made the attic floor air tight and probably can do the same to the eaves (if I can get around the air handlers) but I cannot make the slant area air tight since it is not really accessible.
Lastly, I am contemplating a new roof and could conceivably add external rigid foam but then I have the concerns about placing foam on both sides of the roof sheathing.
Tim,
It's an awkward situation, for sure. In short -- that's no place for an air handler.
You have lots of choices, but none of them are cheap.
Martin, the house is 90 years old and basically the roof sheathing has been unventilated and exposed to internal moisture, and conditioned air all of this time without apparent detriment. Do you think that my best approach would be to spary foam the knee wall ceiling rafter bays, fill the eaves front and back, tape the air handlers as best I can and simply accept an unvented roof sheathing and hope for the best at the slant area?
I would consider moving the air handlers if there was some place to move them to. I also would consider a new roof with external foam board although I know that there still will be leakage at the external wall roof junction no matter what I do.
Your best short advise would be appreciated.
Tim,
It's impossible for me to offer the best solution without a site visit.
If possible, bring the air handler into the thermal envelope of the house by installing spray foam insulation where necessary. If that's not possible, consider moving the air handler.
If neither of those options is possible, you may have to settle for a compromise situation that isn't fully satisfactory. Anyone who lives in an old house makes compromises like that all the time.
Tim,
If you are replacing your roof, you have the option of removing the planking over the spaces you can't get to. This will allow you to remove any old insulation from behind your sloped ceilings and replace it with a layer of spray foam applied to the back of the drywall (lath or whatever it is) If you use closed cell foam you can get a decent amount of r-value and still leave a ventilation gap to feed your upper attic.