HELP - high loss in attic ducts

S. Orbine

I have a new home - 4000 SF heavily insulated, with 2 air handlers (1 per floor) with hot water coils. The heat bills are quite high. It turns out the 2nd floor system has high heat loss. The air handler and ducts are located in cold attic space. I made some temperature readings as follows:

Attic temp: 32 deg f
return air temp (at register): 71 deg F
return air at air handler: 63 deg F
supply air (36" from hot water coil): 158 def F
supply air (at register): 142 deg F

The air handler is running at 1100 cfm, so you're talking about substantial btu/hr loss while the system is running, and probably some loss when it's not running due to convection flow. The flex ducts are mostly R6, some R4.2, the hard ducts are wrapped (tightly=bad) with R6.

Now the question: Is there a good way to insulate the ducts? Are there like R20 flex ducts available? I would consider replacing the entire 2nd floor with hot water baseboard, bu that still leaves the AC in the summer. Any suggestions out there?

Constantin

Here is what I would consider...

... if you don't have asphalt shingles on the roof, you can insulate the roof deck from below and make the attic part of the conditioned space. Then, insulating the cabinets, ductwork, etc. is no longer as important. Blowing icynene into rafter bays is very easy and makes for an air-tight seal.

If this is not an option, consider properly sealing the attic-to-2nd floor ceiling interface. Get a thermal camera, pinpoint leaks and seal them shut. Expanding foams usually work best, because they are impermeable, while fiberglass allows warm air to pass. Also, if there isn't something like R30-40 of insulation up there, consider blowing some in... dense-pack cellulose is cheap and infiltration resistant.

For your ductwork, consider Aeroseal, which appears to be a nifty technology that does duct sealing from the inside by blowing an aerosol into the ductwork that clumps on leaks. However, with the return temp being as low as it is, it sounds to me like there is a return or two that has gotten disconnected. This is what I would check for first.

Weezbo

Where are the coils and air handeler 's Located?

S. Orbine

York 4-ton variable speed air handler running at 1100 cfm is located in unconditioned attic space. Hot water coil is about 2 feet downstream of the air handler output.

S. Orbine

Roof is (50yr timberline) asphalt shingle.

The 2nd floor to attic is R30 w/ 3/4 plywood (attic floor) over about two-thirds, and R38 elsewhere. The attic floor is not in question at the moment, I'm looking at the duct loss.

That Aeroseal is very interesting. I'd like to know how much loss is leakage, and how much is lost throught the duct walls. I figure (an educated guesstimate) that there might be 900 to 1000 square feet of duct wall. Some is R4.2, some is R6, some (air handler, etc) has no insulation. Figuring R5 on average, 1000 square feet, wouldn't that account for almost all the loss?

I did one other test: I ran the air handler but shut off the hot water supply. I gave it 20 minutes of running to stabilize, and found 70 degrees going in, 55 degrees coming out. (again 32 deg attic temp.) There are no obvious big leaks.

It seems like the best solution for heat and cool would be to move the ducts into their own insulated space.

Weezbo

i am liking your idea of a dedicated space,

especially an insulated dedicated air space,with an eye to easy service . Constantines word on the Aeroseal would cover any loss along seals in the distribution piping that may some how have been overlooked during installation. i do not know the way to direct you to a link however this is just some "food for thought....look under a recent post regarding radiant walls,scroll to Hot Rods entry click on the existing link how to get there from here this site Has the right notion for the healthy environmental home,perhaps some thing will be especially useful ,or give you a picture of a ready made answer....