Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 04-05-2009, 06:16 PM   #1
Newbie
 
Join Date: Jul 2006
Posts: 29
Share |
Default

A/C struggles in hot weather


My house has dual HVAC zones, and when the weather gets really hot (upper 90s with humidity), the unit in my attic struggles to cool the upper level. The inside temp starts to creep into the upper 70s, and the unit runs non-stop. I had 2 attic fans installed a few years ago, and that helped. I noticed that my attic is insulated to R30, and I am wondering if going to say R38-R40 would make a noticeable difference with my upper unit A/C. I guess at some point there are diminishing returns on insulation.

Would it be worth the cost to get a contractor to blow in more attic insulation? If so, what would be a reasonable cost per square foot to go from R30 to R40?


Last edited by kennelm; 04-05-2009 at 06:19 PM.
kennelm is offline   Reply With Quote
Old 04-05-2009, 06:25 PM   #2
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 9,073
Default

A/C struggles in hot weather


Have you had the unit properly serviced? Freon level needs checking etc etc. More insulation is better but you have to phone some contractors for prices. The ducts in the attic should be checked to make sure they are properly sealed, now is the time to do it and not when it gets HOT.

yuri is online now   Reply With Quote
Old 04-05-2009, 06:30 PM   #3
Member
 
Join Date: Mar 2009
Location: Pennsylvania
Posts: 719
Default

A/C struggles in hot weather


Every unit struggles in 90-100 degree weather and runs most hours of the day.
Depending where you live design conditions in a lot of areas of the USA are 95deg.

In addition I would say tighten up your house, insulate good, and make sure your equipment is clean and running as good as it can.
SULTINI is offline   Reply With Quote
Old 04-05-2009, 06:51 PM   #4
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,615
Default

A/C struggles in hot weather


the coil on that air handler can only do 18F difference on the entering and leaving air and you need to verify that the return air is true space air and noting from the attic is being be sucked in to jack that return up.do you just have a single return grill in the 2nd floor hallway,and does it go right into the back of the air handler.then the suply ducts are they insulated flex runs with minimal elbows and turns.the charge has to be up to operating levels if anything less your tonnage is less in doing that 18F split.if your condenser is being banged by the sun that adds to the operating conditions compared to a shaded area...start with the ducts then get the charge checked. 18F air splits on the air handler(drop) as mentioned then 10F on the condenser(rise)
biggles is online now   Reply With Quote
Old 04-05-2009, 07:43 PM   #5
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,546
Default

A/C struggles in hot weather


Have the unit sericed.
Also have the duct work checked for leaks.

Then also seal up any air leaks you can find in your house.
beenthere is online now   Reply With Quote
Old 04-06-2009, 07:34 PM   #6
Newbie
 
Join Date: Jul 2006
Posts: 29
Default

A/C struggles in hot weather


As recommended, I am getting the unit serviced. Meanwhile, no one has offered an opinion on the merits of increasing the insulation from R30 to R40. Would this be a worthwhile investment? Or is R30 "good enough"?
kennelm is offline   Reply With Quote
Old 04-06-2009, 07:59 PM   #7
HVAC / Plumbing
 
Join Date: Feb 2009
Posts: 1,801
Default

A/C struggles in hot weather


just opinion. Every little bit you can do will help. I doubt you'll really notice any difference & pay back will probably take years.. You already have R30 which is far more than most ( atleast in my area) All your duct work ,coil etc, is in a hot attic. If the duct work is metal . Your a/c has to cool all this metal down.. If I were going to insulate anything, it would be an outside wrap of the duct work & coil
kenmac is offline   Reply With Quote
Old 04-06-2009, 10:25 PM   #8
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Default

A/C struggles in hot weather


Attic fans?

The air being displaced in the attic has to be replenished from somewhere. I know you have R30 but you are actually pulling air from the upper floor into the attic. You are actually adding more infiltration load.
__________________
Just slow, not stupid.

Last edited by hvaclover; 04-06-2009 at 10:27 PM.
hvaclover is offline   Reply With Quote
Old 04-07-2009, 01:33 AM   #9
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,546
Default

A/C struggles in hot weather


Quote:
Originally Posted by kennelm View Post
As recommended, I am getting the unit serviced. Meanwhile, no one has offered an opinion on the merits of increasing the insulation from R30 to R40. Would this be a worthwhile investment? Or is R30 "good enough"?
If your attic reaches a temp of 150F, and you keep your house temp at 70F.
Increasing from R30, to R40, lowers your heat gain by 1,000 BTUs total, on a 1500 sq ft ceiling.

Not a cost saving thing for cooling alone.
And only helps the A/C minimally.

Sealing air leaks in your home will do far more to save you money.
beenthere is online now   Reply With Quote
Old 04-07-2009, 08:41 PM   #10
Newbie
 
Join Date: Jul 2006
Posts: 29
Default

A/C struggles in hot weather


Quote:
Originally Posted by hvaclover View Post
Attic fans?

The air being displaced in the attic has to be replenished from somewhere.
Isn't that what the soffit vents and the end gable vents are for?

Quote:
Originally Posted by hvaclover View Post
I know you have R30 but you are actually pulling air from the upper floor into the attic. You are actually adding more infiltration load.
Well, I noticed an improvement after the vents were installed. It definitely pulls that super-heated air from the attic...
kennelm is offline   Reply With Quote
Old 04-07-2009, 08:52 PM   #11
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,546
Default

A/C struggles in hot weather


Is it making the first floor unit work more though?

Seal your attic access(weather stripping).

I like power vents for attics also. But, they do pull air from the occupied area, if the house isn't sealed right.

The sofit vents, are generally only installed)(sized) for natural convection. Not powered exhaust.
beenthere is online now   Reply With Quote
Old 04-07-2009, 08:58 PM   #12
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Default

A/C struggles in hot weather


Quote:
Originally Posted by kennelm View Post
Isn't that what the soffit vents and the end gable vents are for?



Well, I noticed an improvement after the vents were installed. It definitely pulls that super-heated air from the attic...
Yeah but it's only an incremental improvement and your unit is running more in proportion to the improvement . Put plainly, your paying more for the slight improvement in longer run time.
__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
Old 04-07-2009, 09:12 PM   #13
HVAC / Plumbing
 
Join Date: Feb 2009
Posts: 1,801
Default

A/C struggles in hot weather


Quote:
Originally Posted by beenthere View Post

The sofit vents, are generally only installed)(sized) for natural convection. Not powered exhaust.



Yep, he needs air exchange depending on how much air his power vents move or remove...
kenmac is offline   Reply With Quote
Old 04-08-2009, 01:55 PM   #14
30 year tech
 
hvac122's Avatar
 
Join Date: Dec 2007
Location: Lincoln, Nebraska
Posts: 427
Default

A/C struggles in hot weather


Quote:
Originally Posted by kennelm View Post
Isn't that what the soffit vents and the end gable vents are for? As said they were designed for passive ventilation only. They are not big enough for power ventilaters,



Well, I noticed an improvement after the vents were installed. It definitely pulls that super-heated air from the attic...
Yes the attic is cooler but studies have found that your pulling around 20% of that air from the house through the attic floor. This is air that you have already paid to condition. This also could put your house in a negitive pressure which could cause health problems and unsafe conditions.

You would be much better off sealing the attic floor (remove insulation, seal and then put insulation back. Also installing a radiant barrier at the roof line will stop the infrared infiltration through the roof.
hvac122 is offline   Reply With Quote
Old 04-08-2009, 05:12 PM   #15
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Default

A/C struggles in hot weather


There is a Law of Diminishing Returns for insulation and a lot of other things; the first dollar you spend on insulation gives you a lot more benefit than the last dollar.
http://www.energystar.gov/index.cfm?...sulation_table


Last edited by Yoyizit; 04-08-2009 at 05:18 PM.
Yoyizit is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
replacing weather stripping on front door cao911 Remodeling 5 09-07-2012 04:29 PM
Oakland/East Bay weather vs. Seattle brooklynsual Off Topic 2 12-06-2008 10:01 PM
Oakland/East Bay weather vs. Seattle jek.don Off Topic 1 11-11-2008 12:58 PM
Weather Head problem. integlikewhoa Electrical 5 02-18-2008 11:08 PM
Wiring weather heads and meters rick32 Electrical 7 09-17-2006 07:27 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.