I have a problem keeping the second floor of our house cool in the summer with air conditioning, especially during these recent hot days. The second floor is noticeably warmer than the first floor, usually 5-10 degrees. I want to get some opinions on some solutions to this problem.
The house, built in 1993 in southern Ohio, is about 2400sf with 3 bedrooms on the second floor. It has a geothermal heating/cooling system which works really well and is efficient, except for the second floor problem in the summer. The system is not zoned, and the thermostat is on the first floor. All of the second floor bedrooms have both a floor register and return air ducts in the ceiling, in addition to a return air duct in the hallway. The walls are standard 2×4 with fiberglass insulation with ½” foam board insulation over that. The attic insulation is blown-in to a depth of 6-8 inches, probably not enough, but I read somewhere that more may not help much with this problem. Last year I installed a whole house fan in the second floor hallway ceiling, this of course only helps when the temperature outside is less than the temperature inside (on cooler evenings).
It seems to me that I need to get the heat out of the attic. Some possible solutions I have looked into include an attic fan that automatically runs during times of high temperature and humidity, and stapling a foil radiant barrier to the bottom of the rafters to shield the attic from the heat absorbed by the shingles. What is the effectiveness of each of these remedies? Is there anything else I should look into?
Thanks in advance for your help.
Phil Riley
Replies
You might have to restrict the airflow to the ground floor somewhat during the summer.
Well, if you have an open stairway, this is going to happen. In our house, if you stand under the second-floor balcony you can feel the cool air pouring down to the first floor. Assuming you have cold air returns in every room, if you keep all the doors closed on the second floor and allow them to have their own circulation they will stay a lot cooler. You can also use Chinese-style screens to reduce the layering effect and flow through hallways.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
6-8" of fiberglass insulation is not going to do much to reduce the cooling load on your house, never mind the 2d floor...
if i were reinsulating your house i would ADD 12" - 16" of cellulose right over the top of the fiberglass..
fogeddabout whole house fans..
if you want to vent your attic add soffit and ridge vents.. if you don't want to vent your attic don't.. but you are NOT going to lower the temp. of the attic appreciably at ANY time when you have the sun directly overhead on a summer day..
you can prevent that heat from penetrating your 2d floor ceiling..
the same thing is also true for your winter heating load...oh.. and BTW.. you can have that much cellulose blown in for not much more than the cost of buying and installing a whole-house fanMike Smith Rhode Island : Design / Build / Repair / Restore
Phil,
Just a note of sympathy and shared experience as I am very frustrated by the same problem right now - and I just spent $6k on a new HVAC system which I had expectations would help me on this issue and it hasn't.
I have installed a power attic/roof fan and found that my attic has gone from an average of 140-150 degree to around 100-105, though I can't say it's had any discernable effect on the heat "push-down" into the second floor loving space.
One thing you might try: see if you have two trunks coming off your plenum; if so, chances are good that one may serve the second floor and the other the first floor. If this is the case, a damper installed on the first floor trunk may help direct more air up the other trunk to the second floor.... cool air will fall so you won't notice much loss on the first floor probably. Just be aware of not cutting off too much air or you'll not get enough air moving over your coil and freeze it!
I explained how unhappy I was with my HVAC contractor (having just spent six grand) and the only thing he could suggest was installing a supplemental AC-only unit in the attic (at a cost of $3500+) so I told him he was nuts. He said he did the right sizing according to Manual J, etc, but that on 100 degree 95% humidity days it was not realistic to expect the upstairs temp to be able to hit 72 degrees and that's just the way it is.
In the meantime, I'm just hot - boy do I sympathize with you!
Jcd
"...............the second floor loving space."
That would be the bedrooms, right ???
Oops! (ROFL) Freudian slip?
Thanks for making me laugh out loud today!
Cheers,
Jcd
I know this may kill efficiency, but what about adjusting some vents? Close off every other one downstairs, or make them all half-open. I've had success with this, albeit on a smaller scale, in apartments where the room with the patio door got searing hot, whilst the other shaded rooms were icy. The upstairs/downstairs problems seem prevalent. I have also heard of a "puller" fan installed in vents/ducts to get more air to a specific spot, such as the upstairs. Couldn't you also install a valve in the ducts and/or returns to "balance" the air distribution?
That said, I've worked in ultra-high-tech labs for many year, with the most sophisticated HVAC systems, electronic real time remoted controls, 2x overcapacity for planned heat generating equipment, and the like, and the temp still fluctuated +-5 degrees or worse on a given day. I think it is more of an art . . .
Phil,
With the exception of thatguy, everyone gave you pretty good advice. This is a classic problem with a single zone HVAC system handling different zone with different requirements (I bet your basement is real cool, right?). It is a compromise because installing two separate systems is too expensive for most, the zoning systems available to convert a residential furnace/AC to a zoned system are expensive and not very common and you only get one thermostat. Agravating the problem is that most two story houses have big open stairways, and warmer air rises. I have a slight version of this in my house.
IMHO, the thermostatically controlled attic fan is an expensive noise maker and not worth the box it comes in. Properly venting and insulating your attic is a very good thing to do, but will not affect this problem.
You can 1) close first floor supplies and second floor returns and cool your house from the top down (if you dont have registers, i.e. grilles with dampers, in you supplies and returns, I would suggest changing them). Closing the doors will help but the thermostat on the lower floor will always be satisfied before the upstairs is as cool, 2) have a zoning system installed with a separate zone/thermostat for each floor.
Those are the most practical approaches that I know of. IF the installer did a good job, you should have volume damper in the main branches of the supply ductwork that you can adjust to help force more air upstairs. I chose to do the former and it works pretty well. All my first floor supplies get closed (or mostly closed) in the evening, before I plan to go upstairs. When I'm not home, I cool top down. When I get home, I open the registers in the lower level and since they are closer to the air handler (and I balanced the system with dampers in the ducts) I get more air out of them.
Do the opposite in the winter.
Tim-
You said everyone gave him good advice with the exception of me, and then go on to tell Phil to do exactly what I said to do. Am I missing something? I said close some downstairs registers, and add a valve(i.e. damper) to balance the airflow. Isn't that exactly what you said?
Not grumbling really, just curious!
"Am I missing something? I said close some downstairs registers, and add a valve(i.e. damper) to balance the airflow. Isn't that exactly what you said?"
Yes, pretty much what you said is good advice, though some of the terminology is wrong, you have the right idea, and I should not have pointed you out, but you also said,..
"I have also heard of a "puller" fan installed in vents/ducts to get more air to a specific spot, such as the upstairs."
Such things exist, true, but not a good option or a good recommendation. Duct fans and blowers have specific applications. This is not one of them.
And yes I am splitting hairs, but the total is the sum of the parts. No offense meant.
Can anybody recommend a good book on HVAC?
-- J.S.
John, I can recommend three,
The best basic, general HVAC books that I know of are, in order of my preference:
The TRANE Air Conditioning Manual
The ASHRAE Handbook - Fundamentals
SMACNA "HVAC Duct Systems Design"
The are very specific interest areas that are covered more completely in other publications.
Tim
Thanks, I'll look for them.
-- J.S.
"...a damper installed on the first floor trunk may help direct more air up the other trunk to the second floor..."
This is what fixed (or at least improved) the problem for me.
Mine was a bit more complicated because of other issues (read: poor installation of duct work). We had a single main trunk coming off the blower. The duct work serving the second floor was simply sitting on top of the main trunk with nothing to divert the air up.
Picture it if you will: Main trunk line running horizontally along basement ceiling (bottom of 1st floor joists) with supply lines branching off for each first floor room. To conect the supply for the second floor, the genius who did the work simply cut a hole in the top of the main trunk and taped some more duct over the hole, ran it horizontally for 12ft. or so untill he could get it to where it needed to be to run vertically up to the second floor.
Last summer, we had no problem getting the 1st floor down to 71 degrees, but the second floor wouldn't get below 80. What we finally did was split the main trunk into two dedicated lines - one for each floor - with a damper in the first floor line. Now we simply choke the first floor supply off a bit to get more air flow upstairs.
Now, I should add that we also discovered problems with the return which most likely also contributed to the problem. We decided that relocating a second floor return vent might help. In tearing open a wall in order to do so, we discovered another little problem. Apparently the 2nd floor return had been relocated once before. It had originally been located in a wall that was now inside a closet. Evidently, when the closet was built, and the return vent moved, rather than close off the original return vent, they simply closed it up within the wall. So, I had a wide open return vent inside a wall cavity.
With both problems repaired, the second floor has been much cooler this year - even with the 90+ degree heat we've had for a while.
We're now nearing completion on an addition to the house and the HVAC contractor has decided that splitting the return into two dedicated lines will further improve efficiency. As it stands now, the second floor return simply ties into the first floor line. He's told me that the blower is "starving for air" and having a separate return line for each floor will help with that...we'll see I guess.