Replies

1. 
   bill_burns | May 05, 2001 03:02pm | #1

   *
   if your ac unit is in the basement, your return vents from upstairs may be inadequate to pull hot air down from ceiling on second floor. they might not be high enough, or large enough.
   you also may have undersized supplies to this area.
   second floors are usually warmer, but should not be hot. you might want to have an ac guy check system and see if it is functioning well and is balanced for flow.

1. 
   Mongo_ | May 05, 2001 04:10pm | #2

   *Ron, Most attic spaces suffer from radiant heat gain. The sun heats the shingles, the shingles transfer the heat through to the sheathing. With the sheathing being a higher temp than the ambient attic space, the sheathing essentially becomes one huge radiant panel, radiating heat into your attic space. Yes, there is also some heat gain from conduction and associated delta-T convection...but radiant appears to rule in most attics.Venting the attic air usually does not help much at all. Adding more FG insulation is mostly ineffective as well, as FG is essentially transparent to radiant heat (the spun glass fibers trap air to limit convective heat, but do nothing for radiant).Here's the rub...I've read pro/con sides to the following and have heard the same at trade shows/seminars:To stop the radiant gain you need a radiant barrier. This can be done by installing a foil-faced (radiant barrier) material in eachg rafter bay, with an air space between the foil and the underside of the roof sheathing...often foil-faced RFBI is installed as part of the soffit-to-ridge air chamber between rafters. If your attic insulation is on your attic floor, some simply lay the foil over the insulation on the atic floor. The effctiveness of the foil decreases as dust and dirt collect on its surface.Another option is cellulose insulation. For the most part, radiant heat can not pass through cells, it's absorbed by the uppermost portion of the cells. In my practical experience? An attic with cells is cooler than an attic with FG. An attic with foil-faced RFBI and cells is cooler than an attic with just cells.Then, there is the option of using light-colored shingles on your roof...

1. 
   ChuckT_ | May 05, 2001 04:33pm | #3

   *How about some opinions on adding a second system in the attic? I'm considering a second system to resolve a similar problem that I have on the second floor. I wouldn't say it's hot, but it's a good 10° warmer up there. It seems to me that my problem is lack of quantity of returns and sufficiently sized supplies; not to mention trying to push cold air uphill. Any thoughts on this?

1. 
   Courtney_Ostaff | May 10, 2001 03:03am | #4

   *I once lived in a room that had the secondstory central heat/ac close by - the noise and heat radiation was hell....ie insulate the living areas from heat and sound....

1. 
   Rob_Susz_ | May 11, 2001 06:25am | #5

   *Here's my thoughts Chuck T.You may be right, in fact it's probably a guarantee that the ducts are not sized properly. The fact that they all leak isn't helping either. But it comes down to one thing... cost.A mechanical fix has a significant up front cost and continued opertaing expense FOREVER!Fixing the envelope (with spray foam or cels) costs usually less, reduces the heat load and REDUCES operating expense. Furthermore, once the heat load is reduced, the bad ducts will be closer to being good ducts.The mechanical fix seems deceptively easy, but there is always a downside.-Rob

2. 
   Bob_Carney | May 16, 2001 04:34am | #6

   *Chuck - I went up with a 2nd storey addition 6 yrs. ago for a master bedroom, huge bathroom, and kids room. The existing system I had was forced air located in basement with no central air. The house is approx. 90 yrs. old with all vent openings in floor. Since the new layout of the 2nd flr. walls were not very much in line with the existing 1st. flr. walls, and talking to numerous HVAC guys, we decided to add a seperate air handler, coil and ductwork in the attic and downfeed the entire house with central air. Even though we have a lot of cathedral ceilings and 6 skylights in the new 2nd flr, you could hang meat up there. It works great. But it was pretty expensive to furnish and install. I think what also helps is we put all AC supply and returns either in the ceilings or high up on the walls on both floors, and all the heat supply and returns are in the floor. This takes advantage of the natural properties of cool air drops and warm air rises. Even though it was expensive, I would do it again. Good Luck BOBC

3. 
   Jim_Hassberger | May 16, 2001 08:34pm | #7

   *A few years ago we added a second floor. Prior to the addition, we added central A/C to the original house. Anticipating the 2nd-story addition, our HVAC guy recommended a unit large enough to support the additional load, and suggested we "zone" the system when we added the 2nd unit. By the time we went up, he was retired, and no local HVAC contractor wanted to touch a zoned system. Most recommended a 2nd system for the upstairs.For both cost and space reasons, this was not a great option. We ended up running off the existing unit, but with an in-duct booster blower in the main upstairs supply line, operated off a separate upstairs thermostat. Works great. When the downstairs wants HVAC and the US doesn't, the US blower stays off and relatively little HVAC is wasted on the US. Of course, the upstairs only gets HVAC if the main (downstairs) T/S calls for it, but thats never been a big issue.

4. 
   Matthew_Willahan | May 17, 2001 03:15am | #8

   *well the reason the 2nd floor is hot,,, is because you had a sex... and it cause 200% huminty,, hee hee,, no offense,,

2. 
   Ron_Jacovetty | May 17, 2001 03:15am | #9

   *
   I have a 4 yr old 2-story home with hip roofs all around and only ridge vent w/ continuous vented soffit. The 2nd floor stays very hot, even when we run the AC. It's 3300 sq. foot total, nothing in attic but insulation (no duct work, etc.). I'm thinking about power venting but a search of this site shows alot of negative opinions on power vents and few if any positives. Would another layer of fiberglass insulation be a better investment? Ridge vent is the stuff that comes in a roll. I live in Cleveland so a whole house fan wouldn't help much in August when in August when it stays hot at night with 100% humidity. Thanks in advance for any advise.