View Full Version : Need some help getting my upstairs cooled...
07-11-2007, 02:25 PM
My home was built in 1996. It is a 2 story 2000 square foot home. I am the second owner of the home and have lived here for 6 years. For the entire time, when summer time comes, the house has a very hard time cooling the upstairs (never a problem heating in the winter).
I have a Carrier AC that had its coils replaced 3 years ago.
I thought the source of the problem was probably a few things.... 1) poor airflow upstairs, 2) heat from windows, 3) attic heat seaping down into the rooms.
Over the past year, I have done the following:
Installed a zoned system. I did this myself, and the airflow upstairs, when the downstairs zone is not calling for cool, is much much better than before. This seemed to make the heating equalized for the first time in the summer. It did seem to improve cooling upstairs in the moderately hot times (85-90), but on 90+ degree days, the upstairs would start to warm up around 3 PM, and peak around 9-10PM (the upstairs always get hot AFTER the peak of the day).
I then installed GILA window tinting on all upstairs windows, and installed blinds on any windows that did not have them. A little more difference was noted, but not too much.
I installed an attic fan [1600 CFM] (I already have soffits).
I then had my attic blow to an R-49 rating.
All this added together has made an improvement, but my home still gets warm upstairs. I installed a remote temperature relay so I could see how hot the attic is getting. This was done unfortunately after the attic fan was installed, so I don't know what the temperature was before the fan. On the hottest days (around 98 degrees), the attic will see a temperature around 120 degrees. This is kinda what happens:
around 9AM after a previously hot day (90+ degrees):
Downstairs unit set to 73. Its not calling for air.
Upstairs unit set to 73. Its not calling for air. it spent the night getting the temperature back to normal.
The day is going to have a high in the mid nineties.
from 9AM-Noon, the upstairs controller only calls for air every now and then. temperature remains around 73. By this time, the attic has already peaked 90 degrees.
Around 1-3PM, the upstairs begins to slightly warm. The controller calls for cool, and starts to get behind the curve (the unit is calling to maintain 73 degrees, but by 3 PM, the upstairs is up to 74.5).
the downstairs controller starts to call for air every now and then, but maintains 73.
From 3-5PM, the upstairs starts to go around 75 degrees. The attic temp is peaking around 110-120. The downstairs controller starts to cycle more often.
After 5PM. Both controllers call for cool.
After 7PM. The attic has cooled down around 15 degrees. Both controllers call for air, and both units can't maintain. The upstairs is now around 77-78 degrees, and the downstairs is 75.
after 9PM both units start to catch-up, and the temps start to drop, but it is not uncommon to see the temp upstairs over 75 until around 11PM, sometimes later if the day was really really hot.
I have typed all this, so its possible this can give you a better idea of the source of heat and how to deal with it. Buying a new unit is not an option at the moment. Thank you very much for reading.
Model numbers of all equipment might help.Pictures often help as well,usually the indoor unit and connecting ducts.
Be aware that this is not a DIY site,so no step by step instructions are allowed.
Does you zoning system have a bypass damper,if so it may be opening more then it should,causing reduced air flow at times.
Kneewalls ,if any need sealed insulation over any fiberglass batts,or adding more will reduce the load.
Some homes with partial second floors have "floor trusses" that allow hot air from the first floor attic to circulate under the floor of the second story.If that's the case ,the floor trusses should be sealed off.
Having a Pro out to test the static and select the correct fan speed from the mfrs. fan data chart,might increas the air flow to the second floor.
Could be that there's a lack of return air from the second floor,simple test,if it cools better when all doors are left open,you need a return or return path.
Also if supply air is reduced ,when the door is closed,likely need a return or return path.
07-11-2007, 03:06 PM
Understood on the DIY. I am looking for some general thoughts of what to look for. I will get the model number of the Carrier unit, but am at work at the moment and do not have it.
There is no bypass duct for the zoned system. At the time of install, the manufacturer of the zone control didnt recommend one based on my setup. Its been running this way for a little over a year now.
I dont have any knee walls and I dont have a partial second floor.
I do think the upstairs cools better when the doors are open.
The fact that when both zones are calling you can't get to set point ,would indicate that it's undersized for the temps you want to maintain,or you air flow is lower then it could be to get the maximum btus.
What type of filter do you have?
07-11-2007, 03:45 PM
very inexpensive high airflow filters (they dont do much filtering). I replace them about every 2 months. Changing them doesnt seem to make much difference.
I will say that the unit manages to keep the setpoints on days up to around 90 degrees. Then it starts to fail.
Sounds like you've done what's practical to reduce the load upstairs,which is a good start.
What size main ducts go to each floor?
Is part of the second floor over a garage?
07-11-2007, 04:07 PM
I would measure & log the temperature of air coming out of every single register, and the temp for each return. Do this with the AC running at sunrise (so attic etc. temp is not a factor), then repeat at about 5PM during the peak cooling demand.
These measurements will speak volumes.... or lack of airflow volume.
07-11-2007, 04:16 PM
The main ducts are 12". The garage is below some of the rooms, and the garage gets very very hot. My next plan of action was to install a fan in the garage, that would pull air from some vents I would install in the garage door and circulate the air. The garage has long been a suspect, but I dont think I've seen many people do anything to regulate the temperature of a garage.
gone: I'll see if I can get a register thermometer and get those within a few days.
07-11-2007, 04:21 PM
Just a question: Do the upstairs rooms have returns in each room? Since you say you have poor airflow upstairs, I would get the house air balanced. Doing this will tell you if the system is not performing, or is undersized, if the duct work is correct.
07-11-2007, 04:24 PM
I want to make sure I am understanding the terminology. By a return, you are referring to the place that air is returned to the AC, correct? There are registers in each room, but only one return at the peak of the upstairs steps.
And I wouldnt say the actual air flow is that bad. I had the guy who installed the coils come out and check my unit (before the lousy one year warranty went out on those things) about 4 months before I installed the zoned air control. He measured the air flow at the registers, and said he thought there was plenty of air. from my observation though, I thought the airflow lacked, but it wasnt non existant. after the zone control install, with the downstairs damper closed, the airflow upstairs is very signficant. even very significant airflow isnt enough to overcome the heat. In other words, if both controllers are calling for cool, and I shut off the downstairs controller, the increased flow to the upstairs registers is not enough to make any real difference once the temp upstairs is really high. The air coming out of the vents is not as cool as it is in the morning (which I would expect)
07-11-2007, 04:29 PM
There are several issues involved in ducting a home. Of course, the first thing is to run a Manual 'J' load and determine what size equipment is appropriate. The very next issue, based on that same load calculation, is how much air needs to be introduced to each individual room. This could be an issue in your home. For example, if the whole house needs 3-tons of AC and the downstairs supplies are set up to allow 2-tons of air and the upstairs just 1-ton, the system will work fine UNLESS the 2nd floor really need 1.5-tons. In that case, the downstairs cools just great but the upstairs is behind the eight ball. Okay, so let's zone the system. Remember, the 2nd floor ducts are only designed for 1-ton of AC but you need 1.5-tons. If you've done your by-pass or relief strategy properly when zoning, then 1-ton goes to the 2nd floor and the rest is by-passed or dumped. So yes, the 2nd floor can now command the system to operate instead of waiting for the 1st floor to heat up but you still don't have enough supply engineered into the system by design.
The final thing is return air. Many homes that were originally set up for heatingn only and had AC added later, have little or no return air on the 2nd floor. The designer relied on warm air rising to help the inadequacy of no return on the 2nd floor but when it comes time to extract the warmest air and treat it for AC, well, you can see that's not going to happen if there's no return air. I suspect that if your system is otherwise properly charged and opearating mechanically as correctly as it can, then your problem is an airflow issue based on one or a combination of the things I've mentioned.
BTW, the company that changed out your equipment or installed it a year ago should be able to tell you where the deficiencies lay and should have been able to forecast the issues you're speaking about. Well, that is, unless they were the low bid. :eek:
07-11-2007, 04:45 PM
The guy who installed my coils is an experienced AC guy that I was referred to by my flight instructor (he happened to own an A/C business, but didnt operate in my area). I will generally get 2 quotes on any major repair, and I did so in this case, but ruled out the other company completely and was happy to see his quote as a little lower ($1200 to replace these crappy coils as opposed to $1350). he was there tasked to replace the coils, and his solution to the cooling problem upstairs was a new unit. I wasnt in the mood to spend $5 grand at the time, so wanted to play around with some more options.
I installed the zone control myself. The one shop I had quote the job wanted $1700 to do work I felt I could do in very little time (it took about 6 hours). What they would have done that I did not do, that is not very difficult, is install the static bypass. I was told by the manufacturer of the zone control system I purchased that they did not recommend a bypass duct on a system my size with only 2 zones. The A/C unit is not great, and I decided that if it died as a result of back pressure, I would probably be better off anyway with a new unit. It costs me around $350 to do the zoning. Biggest aggrivation was installing a new thermastat upstairs, and snaking the wire back down to the zone controller, as well as wiring the transformers for the duct dampers. Had my house had a large unit, or needed more than 2 zones, I would have called a pro.
07-11-2007, 08:37 PM
FYI - You shouldn't be talking about pricing here.
I was told by the manufacturer of the zone control system I purchased that they did not recommend a bypass duct on a system my size with only 2 zones.
That's a sketchy statement for them to make without seeing your duct system. You may need a bypass.
and I decided that if it died as a result of back pressure, I would probably be better off anyway with a new unit.
So all this time you have pretty much assumed that you don't have enough airflow. Take this assumption to the next level - maybe this is why your system isn't cooling properly.
You need load calcs for your home. My master suite is over a 3-car garage in Dallas. I used to think the space was hot in August because of the garage, but after peeking under the carpet & plywood, I found 8" of insulation in the floor. Load calcs proved that the windows were the culprit.
Any insulation between the garage ceiling and the second story floor??
Even if there is ,that portion of the second story needs more air flow then the part above the conditioned space,just food for thought.
07-12-2007, 09:25 AM
Yes, there is insulation between the garage and the rooms above. it is a semi-finished garage (insulation and drywall).
07-12-2007, 09:36 AM
How is humidity?
Ever try turning off that big attic exhaust?
07-12-2007, 10:10 AM
I dont have a precise number, but humdity seems high when it gets hot. The attic was installed less than 4 months ago. It was one of the things that improved the cooling...
07-12-2007, 10:17 AM
You said before, that you added the big fan, then after you added the fan, you increased insulation. A test to see if the insulation is what made a difference by itself, aka shut off the fan, may also result in a drop in humidity.
You can get a rather inexpensive thermohygrometer from Radio Shack. They tend to record max min temperatures and humidity, however the recorded data does not coincide with one another.
If you find humidity drops with the attic fan off that means that fan is depressurizing your house. Your home extends over a garage. Think about the consequences of make up air to your home taking a path of least resistance through your garage. Carbon Monoxide.
It is worth checking out.
That garage with the sun beating on walls, will get hotter than the outside. Attic ventialtion could be pulling that hot garage air up through your floor joists as well.
07-12-2007, 10:30 AM
Sounds like a good idea. I'll do that!
07-13-2007, 06:51 AM
Without taking this off-topic, I have some comments and a question. These issues are exactly what I face in my current, non-air conditioned house. I am getting bids for a heat pump/variable speed furnace system that will be installed in the coming weeks, but I believe I will still have problems cooling the upstairs because my 1996 built house is on a sunny hill (in Seattle) with no trees for shade, with an upstairs media room that generates a lot of equipment heat above a 2 car garage and with summer attic temps that reach 120+ degrees.
I have consistently measured a 17-19 degree variation between the 1st and 2nd floor indoor temps at the end of a hot day, currently without A/C.
Now to the question: Should I not worry about the potential balance problems that may exist until after the heat pump and furnace are installed, or is it possible that the contractor needs to calculate/consider this information before a system can be properly sized? None of the three contractors that came out and handed me a proposal have made any mention of ductwork, register CFM, return locations or general cooling challenges even after I present this information to them. One contractor did do what they called a full Manual J and gave me their calculated heat gain and heat loss numbers with the proposal, but the heat gain BTUs seemed surprisingly low considering the challenges I've faced so far. I'm not sure that a Manual J would include certain considerations such as home theater equipment, high density of persons in room, etc.
I don't want to take this thread off-topic and welcome any PMs if you have a comment. (Just noticed that PMs are disabled, at least for me. Response in thread would be appreciated). Thanks.
07-13-2007, 07:12 AM
the problem youre having with temperature differance is return air (not enough upstairs) and the problem of the system not keeping up durring the peak of the day sounds like its over charged. call your contractor back out and have him do a superheat calculation on it. i bet it will remove more heat after thats done.too much freon in the system will give you ice cold air out of the registers, but it wont remove much heat after the sun reaches its zenith.
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