ceabbott2

Hey Guys,

I built an addition two years ago (standard gable with no eave vents). It's approx 800-900 sq/ft. living space. The contractor installed a 2.5 ton heat pump along with a Trane xv90 blower unit and a trane prog thermostat. The additions living room (485 sq/ft) has an elevated ceiling approx 10.5 feet while the remaining 400 sq/ft has an 8.5 feet ceiling. It's on a concrete slab so all returns are in the walls panned in and the supply comes in through the attic. The blower unit is located in an attached garage that is NOT climate controlled. Over the past two years during the summer months especially when the temperatures exceed 90 degrees the addition will not stay below 75 degrees. If it's 95 outside than it's 77 inside. The rest of the house has two separate split systems (gas furnace with a condenser outside) they have no trouble maintaining any temperature I set them to (FYI return air is in crawl space supply side in the attic). They are both Trane systems I purchased ten years ago from the same contractor. The attic space in the new addition is about half of the size of the attic space in the older part of the house due in part to the elevated ceiling in the new living room. The attic last summer was somewhere between 150-155 degrees (new addition...didn't test the older part of the house's attic). Way too hot! When we added the addition we tore off the old roof on the older section and roofed everything again and we used FULL vinyl soffit vents and a Cobra II ridge vent. The return air and supply ducts run parallel to each other in the hot attic (new addition only). We asked the contractor not to line the inside of the duct with fiberglass (we were worried about breathing issues with loose fiberglass particles) Any way he wrapped the trunks with a foil bubble wrap on the outside. I believe I have two problems: 1) Attic Is Too Hot so I was considering a Powered Attic roof Mount Ventilator with an Thermidastat/Humidistat and wrapping the ducts with some other kind of ADDITIONAL insulation. Am I on the right track? Anyone have any other suggestions? The contractor came out last summer and drilled a small hole in the supply side duct just past the A-Coil and it was cooling properly. So my guess is the extremely hot air trapped in the new attic space and the under insulated ducts are the problems. By the way the supply ducts for all rooms are run from the main supply trunck with 6.0 R factor flex duct???All walls and ceilings have fiberglass insulation in the new part. The old part just has blown in fiberglass in the attic space (approx 30"). Any help or suggestions would be greatly appreciated. By the way I really like my contractor he's a great guy! I just want the AC to work in the summer. By the way when we run the heat pump in the winter we don't seem to have any issues as far as the mini assist (50 amp heater) kicking on all of the time. Thanks guys I appreciate it!

Sincerely,
Charles Abbott

beenthere

Sounds like either its not installed or charged right. or you don't have the insulation you think you have.

What the temp difference across the coil?

naptown CR

This has apparently been checked

I would look into adding more insulation to the ductwork.

ceabbott2

So neither of you recommend the power attic roof mount ventilator? I have r-30 kraft faced between the trusses with 7/16 osb decking on top (light storage). The main supply and return air trunk lines are on top of one side of the decking with flex duct making the connections to the registers and returns. I realize now I should have put the fiberglass inside but I gotta work with what I have. My contractor said he would sell me some fiberglass duct wrap at his cost so I will definately do that. But I thought a very large roof mount attic ventilator could reduce the attic temp by 20-25 degrees. I was definately going to wrap the ducts some more. Thanks again for your expertise. Charles.

beenthere

What ever size vent fan you install. You have to make sure, you have enough air going into the attic.

What temp is the air coing out of the supplies.

ceabbott2

Thanks Beenthere,

One thing I forgot to mention is the system catches up around 11 or 12 at night. I am not for sure if this helps any. I am not for sure what the temp is at the supply side registers. Thanks Charles.

beenthere

IF, you have enough sofit/gable vent that a powered exhaust fan doesn't put air from the house.

It will probably help.

NickTech

a common problem with additions like these are that the heat load calculated doesn't count that the walls and ceilings are exposed areas that allow for more heat transmission than regular walls and attic floors. if the unit is undersized then your temps and pressures will all be the same as a properly sized one. the deciding factor would be the t stat not satisfying in an appropriate amount of time. this sound like the problem here. the return should be evaluated to see if it is pulling the hot air out of the area, also, you stated that when the sun goes down and it finally starts to cool down then thet stat satisfies, this supports the under sized idea. the color of the roof makes a big contrbution to heating the area. try a lighter color roof, roof ventilation or cooling the roof with water. have a contractor come in and do another manual J calc. to dbl check. hope you solve this!

ceabbott2

Thanks beenthere and Nicktech. The roof is weathered wood sort of a brown. I've been wondering about the size of this unit and or the reurn air. There is a return air duct that goes across two studs (panned in) for my living room (22 x 22) with the 10.5 ceilings. Is it possible that I don't have enough return air for this room? Or what do you guys think about the foil bubble wrap just not being enough insulation to keep the steel duct work from absorbing all of the heat in the attic (150 + degrees)? Thanks again Charles.

beenthere

If they wrapped it(bubble wrap) right against the duct.
Your only getting about ½ its R value.

NickTech

right on beenthere, there should be a short strip of insul. there to create more of an air gap to bump up the r value. but with a 150 deg. attic i dont think that would do it anyway. the big problem is this hot attic. take steps to see if you can eliminate that load first.

ceabbott2

The bubble wrap is directly against the duct. Sorry to be a pain but one other idea occured. At the time of the install we used a full vented soffit. I didn't take into account the air coming out of the top of the heat pump is probably going straight up into the attic space via the vented soffit (the distance between the top of the heat pump and soffit is probably 5 to 6 feet). Rather than tearing off and replacingthe soffit could I install some fiberglass in the soffit above the heat pump to prevent heated air from infiltrating the attic space or would it be better to use a non vented piece of plastic? Thanks again guys I keep looking at this thing and coming up with new possible contributing factors. The unit was placed that close to the house 22" because the wife didn't want it sticking out on the patio. I'll defend her in that we didn't know the heat pump would be that large and I had not considered the fully vented soffit vents when I installed them. Thanks Guys I hope this info helps. Charles.

beenthere

You can put non vented sofits in.
Doubt that will help much though.
Depending which bubble wrap they used. You have between an R2 and R4 insulation value.

flashheatingand

The attic is not heating up to 140+ due to the air coming off the heat-pump. You can cover up that vent, but I doubt that will change matters drastically. If your wife wanted the unit tight to the house, it is understandable. I don't like them being tight because debris will build-up on the coil, and can cause premature damage to the compressor. You want to make sure that all sides of the coil are clean. There are a couple of reasons why it's best to leave at least 10" from the side but it's there and the reasons aren't overly crucial.

Have you installed a exhaust fan yet?

ceabbott2

My vacation starts July 2 so I plan on putting in a large 1600 cfm with an adjustable thermostat. Thanks again guys for all of the help! Charles Abbott. You guys are the BEST!

ceabbott2

Well I installed the roof mount powered ventilator. The main room which has the raised ceiling (10.5') the attic space is blocked because the original roof above was never cut out when the new addition was tied into the old house. Imagine two gables ranch style perpindicular to each other forming an L shape. Anyway I am going to go up in the attic and pretend to be Nadia Comaneci and get to where the old roof is still intact and cut the decking away exposing the rafters underneath. When the HVAC contractor ran his two flex duct supplies they just cut squares large enough for the flex duct to fit through. Since the area above the living room has the raised ceiling I think if I can get that area open the powered ventilator may be able to get some of the hot air out of the attic space. I've also decided to insulate the heck out of the attic with blown in celluose (sp) ? I'm thinking 12" on top of the R-19 btts that are between the trusses. I feel if I can insulate the indoor living space and the ductwork in the attic from the hot attic air maybe that will do the trick.
What do you guys think. I'm sure R-19 isn't enough.

MechAcc

Have them measure the air temperature at the return air grilles and then at the return of the air handler/furnace. If you have a significantly higher temperature at the air handler than the return grilles you have duct leakage and the ducts should be sealed.

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