Attic too hot

[mariorangel73]

I live in Houston Tx. My attic is less than 600 sqf and has very little if not no ventilation. It can get very hot up there. This is a townhome, 1200 sqft. I just got a new ac system. 3 ton, 410a, 14 seer. The problem is that during the day there's only a 14 degree differential between the air on the return duct and the air coming right from the vents. Furnace,coil and ducts are in the attic, in a very hot environment Apparently, somewhere in the furnace, the air gains 4 to 5 degrees, and maybe 1 or 2 degrees more in the ductwork. When the temp is taken on the return air is 79 (up in the attic), and in between the furnace and the coil is 84 Is this normal? considering the facts? or could something be wrong with the furnace. The condenser has been checked and everything is normal according to the tech. Does the furnace need more insulation? Can you put extra insulation on the furnace?, or adding a turbine fan to ventilate the attic can improve the performance of the equipment? Advice will be greatly appreciated

[mark beiser]

Some passive ventilation will help, like soffit vents down low and a turbin or ridge vent up high, but ventilation won't reduce the amount of heat entering the attic, and in a humid climate may cause other problems.

Look at getting a radiant barrier installed, either spray on or the foil kind applied to the underside of the roof.
The radiant barrier will block most of the heat from entering the attic in the first place.

Don't let anyone install a powered attic ventilator or a radiant barrier on the attic floor.
The PAV won't solve the problem, and likely will cause other problems.
A radiant barrier on the floor of the attic doesn't keep the heat out of the attic, makes it somewhat difficult to get around in the attic, and looses effectiveness over time as it gets dusty.

[mariorangel73]

So if there are no leaks, could it be consider normal for the furnace to gain 4 to 5 degrees in such heat? or something could be wrong with the furnace itself? can you insulate the furnace?

[skippedover]

So if there are no leaks, could it be consider normal for the furnace to gain 4 to 5 degrees in such heat? or something could be wrong with the furnace itself? can you insulate the furnace?

IMO there have to be leaks into the duct system. Your numbers indicate that the return air is picking up 5 degrees between the RA (you don't say where this is measured or how long the trunk is between the point where you've measuring the RA temperature and the AC coil. Of You're measuring at the RA grille in the room, then the first place to look is at the RA duct. Is it insulated? Don't take "silver color" as being insulated because there are felxible silver ducts that are not insulated. Is it sheet metal or flex duct or fiberboard? Have you taken a measurement between the inlest to the furnace and the outlet of the furnace, before the coil?

[dfw_lr]

Some passive ventilation will help, like soffit vents down low and a turbin or ridge vent up high, but ventilation won't reduce the amount of heat entering the attic, and in a humid climate may cause other problems.

Look at getting a radiant barrier installed, either spray on or the foil kind applied to the underside of the roof.
The radiant barrier will block most of the heat from entering the attic in the first place.

Don't let anyone install a powered attic ventilator or a radiant barrier on the attic floor.
The PAV won't solve the problem, and likely will cause other problems.
A radiant barrier on the floor of the attic doesn't keep the heat out of the attic, makes it somewhat difficult to get around in the attic, and looses effectiveness over time as it gets dusty.





I agree that a radiant barrier wound be a good idea, but I disagree that it [must be installed under the roof decking as opposed to on top of the attic floor.

First of all, while it's true that the attic won't be a comfortable as the living space and will remain hot during the summer, it works to your advantage in the winter. Instead of your furnace just heating the living space, you will be wasting energy by heating the attic as well. If you rarely go into the attic, there is no reason you need to waste the energy to keep it as comfortable.

The idea of dust rendering a radiant barrier ineffective is a common misconception. Radiant barriers don't work like mirrors, where if you can't see it it's not working. Dust particles are small and round is shape, so even when they seemingly cover a surface, there is very little surface contact, and surface contact is what really counts.

Having a radiant barrier at all is a great way to block 95% of the heat, however you install it. I just think laying a perforated radiant barrier over the existing insulation is not only easier to install, but more efficient.

See the link below for a posting on the effects of dust on a radiant barrier.


http://hvac-talk.com/vbb/showthread.php?t=143021&highlight=radiant+barrier

[skippedover]

So if there are no leaks, could it be consider normal for the furnace to gain 4 to 5 degrees in such heat? or something could be wrong with the furnace itself? can you insulate the furnace?

You've never actually said what the attic temperature is. I work in attics on a regular basis with AC units installed and it can be 140 degrees on a sunny day with the metal on an air handler or furnace so hot, you can burn the underside of your arm on it. So just how hot is it in your attic? 180, 190, 200? Can you boil water or fry an egg? Keep in mind that the air is moving through the duct system relatively quickly. Just like you can move your hand quickly over a candle flame and not get burned, the air moving through the duct system shouldn't pick up much heat if the system is properly insulated.

[mark beiser]

I agree that a radiant barrier wound be a good idea, but I disagree that it [must be installed under the roof decking as opposed to on top of the attic floor.

First of all, while it's true that the attic won't be a comfortable as the living space and will remain hot during the summer, it works to your advantage in the winter. Instead of your furnace just heating the living space, you will be wasting energy by heating the attic as well. If you rarely go into the attic, there is no reason you need to waste the energy to keep it as comfortable.

The idea of dust rendering a radiant barrier ineffective is a common misconception. Radiant barriers don't work like mirrors, where if you can't see it it's not working. Dust particles are small and round is shape, so even when they seemingly cover a surface, there is very little surface contact, and surface contact is what really counts.

Having a radiant barrier at all is a great way to block 95% of the heat, however you install it. I just think laying a perforated radiant barrier over the existing insulation is not only easier to install, but more efficient.

See the link below for a posting on the effects of dust on a radiant barrier.


http://hvac-talk.com/vbb/showthread.php?t=143021&highlight=radiant+barrier


Having the radiant barrier on the floor of the attic still makes it a PITA, if not dangerous, to get around in the attic if any work needs to be done.
The idea in my climate, and the OPs climate, is to keep the heat out of the attic in the first place, since that is where most of us have our ductwork and even the indoor equipment itself.

[energy_rater_La]

Intresting study.
I notice that it is a 20% accumulation of dust that is tested on the radiant barrier placed on top of insulation.
My readings have lead to a 50% reduction of reflectivity due to dust build up,
and the common time frame to reach this 59% reduction is 5 years. I would think that would vary depending on many factors.

Personally I had no hesitation in installing my single sided radiant barrier to the undersides of the rafters with foil facing into the attic space.
What a difference it made. Immediately!
And I have been told by the goverment department that I answer to, that a install such as was described (on top of insulation on attic floor) was a waste of time effort & money. Same for installing radiant barrier to undersides of attic with foil facing the roof, dust accumulation was the issue there also.

Radiant barriers have little to no effect in heating seasons in a well sealed insulated attic. (buildingscience.com)

Just thinking it through, why would you want to allow the heat into the attic space anyway? If you can install the radiant barrier on the roof line instead of the attic space, it reflects heat from the roofline, not from the attic floor.
I can't see any savings in misapplying a good product.

Florida Solar Energy Center's website has good unbiased information on radiant barriers, and is a good source for the op as is building science site.

Much good info has been posted for op, stop duct leakage, stop attic to house infiltration, radiant barrier. Power vents actually cause more issues than they solve by pulling air from leakage sites (unsealed ducts, recessed lights, incomplete air barriers into conditioned spaces). That would be the one option I would pass on.

And OP, yes you can add insulation to the heating system in form of a R-6 to R-8 wrap, but I doubt that it would help with your issue.
Stopping leaks in both ductwork and @ attic floor & adding a radiant barrier would be the best direction to go, again IMHO.

thanks for posting the link to the study dwf_lr it was interesting to read their take on the install/product.