Last month I finally got my central air system installed in my 2-story home that is on a slab.

I just started to run the system for a couple hours a day starting Sunday. My system is a 1 zone 3.5 ton Rheem Prestige Series 2 RASL-JEC compressor and RHPN air handler.

I have a Nest thermostat which is located downstairs and I had asked my installer which is a very reputable installer and friend of my fathers in the area if it was OK to keep the thermostat downstairs and he said yes.

I have the temperature at 72 degrees and the downstairs is perfectly comfortable but the upstairs is at 87 degrees and does not seem to be cooling down. I am a bit worried but the wife said lets wait and see what happens over the next month to see if the upstairs begins to acclimate with the downstairs. I don't want to go back to the installer just yet because I may just be freaking out over nothing. Is this normal since the system in not running constantly?

 

Not a HVAC guy, but was a return installed upstairs? If not you need a return. But really I think if its rooms up there you need a return for each room..

Where is the HVAC unit installed?

Best would have been to put a air-handler in the attic just for the upstairs with its own t stat.

IMO your system will never work right if that is the case as stated above about the returns..

 

Air Handler is upstairs in the attic and the return is also upstairs but I don't have a return in each room. Only 2 spare bedrooms and a bathroom are upstairs, master is down stairs so it is not a big problem right now since nobody is living upstairs.

 

The best way to handle this would be to have two A/C units, one for each floor. However, since you only have a single unit (and many people with two story homes only have a single A/C unit), you need to reduce the airflow to the downstairs to better balance the cooling between upstairs & downstairs. Hopefully, you have dampers on each of the runs (upstairs & downstairs). Try partially closing (not completely) the dampers on the downstairs runs, while leaving the upstairs dampers fully open. You'll have to experiment to find the right balance.

 

High temps in the attic will also keep the second floor hot and hinder the A/C process.

 

I have a cape style home and even prior to the central air, in the summer the upstairs would get up to 100+ degrees.

Would it be wise to install a solar gable fan in the attic to remove the hot air? Would it be best to install 1 on each side of the house?

 

It's hard to make a recommendation on what exactly to use, without seeing the application, but reduction of heat in the attic is important.

 

They are useless IMO and a waste of money... They produce minimal CFM...

 

Do you recommend a regular powered gable fan?

 

You should NEVER have such a large temperature difference between floors, especially with the air handler in the attic.

Likely causes: Incorrect duct design and attic insulation/ventilation issues.

Lack of ventilation can be particularly negative impact when there's ductwork in the attic.

What to check:

Ventilation: There should be roof and open sofit vents; sofit vents allow air in to replace what's vented by the roof vents. Sofit vents can easily be blocked with insulation. A decent roofer should be able to check that out for you.

Insulation: You should have at least R-30 up there -> R-50 is preferred. Measure the insulation from the hatch and look up the r-value per inch. (blown in fiberglass, cellulose, and batts all have different r-values per inch.

Air sealing: Seal around all vents, light fixtures, plumbing penetrations, electrical penetration if practical.

A/C system:

Did you have new ductwork installed? Was there an existing system? Did you have the same problem.

The second floor usually needs far more cooling than the first floor - if your contractor just put one vent per room regardless of heat gain, he did it wrong. A room by room load calculation should be done and the ductwork re-done accordingly.

You can try blocking off some of the downstairs vents, but the system needs to move a certain amount of air to work properly.

 

I opened the hatch earlier about an hour ago and I must say the attic and peak is very well insulated, at least 6-8" thick of insulation. I did notice that inside the hatch was cooler than inside the bedroom (how is that possible?).

This is a brand new system, new ductwork and everything. Prior to this I had NO AC.

In the upstairs, all I have is a hallway, a bedroom on either side of the hallway and a bathroom in between. I believe he put in 8" registers on each bedroom and a 6" on the bathroom, nothing in the hallway. I definitely feel the cold air coming out but the hot air is just too over powering and not able to cool down.

I spoke with the installer and he said we can move the tstat upstairs but I don't want to freeze out the downstairs. Something else has to be going on for a 17 degree difference between floors...

 

Probably not. On the capes youll suck the cold air right out IMO..

You have knee walls? Are they insulated?

Bobs post # 4 is the best advice.

But since the t stat is downstairs it will never cool upstairs enough. The t stat will satisfy first. And if you put the stat upstairs you will freeze downstairs..

 

Your in good hands with muggle....

But where is the return on the second floor? Is there a return on the first floor?

Muggle I heard of these types of installs only getting a large return upstairs and none down.. Is that true or does it work?

 

I only have 1 large return and it is by the stairs. Basically in one of the eaves directly above my front door. It's definitely not at the highest point in the upstairs, I've been wondering if that could be the problem.

When it was being installed I asked if it could be placed in the hallway ceiling but it would not fit since the ceiling was too narrow.

 

That's really weird -> did you check it during the heat of the day?

Could there be excessive supply duct leakage? With the system on and the hatch open, do you feel cool air moving into the house?

I think one return should work if properly sized, but it's not ideal. Cool air falls, and the trick is getting the right amount of supply air to each room -> supply air is what actually does the cooling.

You could have a combination of high supply duct leakage, undersized ducts (causing poor airflow and reduced capacity), and a improper system design.

Since your system is new, it presumably has a full warranty -> the contractor should take care of it.

For the heck of it, if you'd like -> post duct sizes and tonnage.

 

What type of ductwork did he use? Did he use a lot of flex? With 2-8s and a 6 upstairs I'd say your CFM for upstairs is way low. What's the size of the bedrooms? I would look into having him add a small return in each bedroom as well, no returns there will really hurt output when the doors are closed. Duct leakage is also a killer for performance. When I do installs everything is hard piped, taped at the seams and then mastic applied on top of the tape. Thats the best way to design and run duct work. I RARELY use flex.

 

Hard pipe has a lower friction rate, right?

To me 8" for a bedroom isn't bad at all, but the overall design of the system is what counts. Sounds like there's too much supply on the main floor, not enough on the second.

 

I have not been home to check, I will tomorrow

The return seems really big, here is a picture:


For the most part everything looks like it is flex except the duct work going up along the roof to get onto the other side of the house.

They are approximately 14x12 each and the bathroom is about 5x6. The hallway is probably 10ft long and 4ft wide. Its not that big upstairs...

It is very possible that there is not enough supply upstairs. there is plenty downstairs. My living room, dinning room and kitchen is one big open floor plan, no walls separating them. I have:

1x 8" in the Kitchen
1x 8" in the Dinning Room
2x 8" in the living room
1x 6" in the Bathroom
1x 6" in the laundry room
2x 8" in the master bedroom
1x 8" in the spare bedroom
1x 6" in the master closet

Below are the registers in the living room:


I questioned the fact that a register (or 2) were not put in the upstairs hallway. Do you think it would be wise to have him put one in? He warranties the system for a complete year so I would say if it is not working to my liking this would be covered correct? Also, he is going to have his electrician come back and move the thermostat to the upstairs hallway where the current thermostat is for the heat.

 

Forgot to include the exact models of the system:

Condenser: Rheem RASL039JEC
Air Handler: Rheem RHPNHM3624JC

 

Wait for the pros to chime in, but I will give my opinion...

I live in a cape just like yours. I know how hot it gets upstairs. I know where your return is and I think that is not a good place...

Actually on the capes I believe all the returns should be upstairs period and none down... One in each bedroom and the bath... Plus hall..

You want to suck the heat out of all the rooms upstairs period...

But it is a balancing act when you are working with one t stat and one zone...But even with that said I would be surprised if it would ever get cooler upstairs then it would down...

But remember cool air will drop. So the cooler you get it up there that air will fall...

But I would like to hear the pros about my suggestion of every return upstairs... ( And you need everyroom, not one..) Also the supply's need to be spaced far enough from the returns so you dont just have air coming in and sucking out. Should be on opposite sides of room...

Thats the challenge with capes, and usually no one takes them on in the HVAC world... Mostly mini splits are used because contractors will loose money on warranty work when they dont do it right the first time. Just as your house is... ( I bet your guy never gets it right unless the whole system is redesigned. And that will cost him money)

 

Thanks for the pictures -> your return setup is far from ideal -> you want it pulling in the hottest air; right now the the return is near floor level on the second floor, so the hot air rises to the ceiling and stays there.

 

Here's the breakdown of your duct setup. I used equal friction method -> ie not taking duct length into account, so the downstairs figures are a little inflated. I also didn't take leakage into account. Also, not sure if the bathroom served by the 6" is up or down.

You have a 3 ton system, which needs 1200 cfm. You have large enough "ducts", but the distribution is probably off.

Total cfm @ 0.08"/100 ft friction = 1260

Figures are in this order: CFM, Percent, BTUs of cooling
Downstairs:
1x 8" in the Kitchen 150 0.119047619 4285.714286
1x 8" in the Dinning Room 150 0.119047619 4285.714286
2x 8" in the living room 300 0.238095238 8571.428571
1x 6" in the laundry room 70 0.055555556 2000
Subtotal: 670cfm 19 142.84

Upstairs
2x 8" in the master bedroom 300 0.238095238 8571.428571
1x 8" in the spare bedroom 150 0.119047619 4285.714286
1x 6" in the master closet 70 0.055555556 2000
1x 6" in the Bathroom 70 0.055555556 2000
Subtotal: 590 cfm 16 856


Now, if the square footage upstairs is the same as downstairs, the second story should be getting a lot more airflow than the first story to compensate for the attic heat gain or convection. At best, down is getting the same as up once duct length is considered.

Had your contractor done a room by room load calc and put a ceiling level return in each bedroom, you wouldn't be having this problem.

Now, dampering down the first floor vents to less than 50% airflow, adding more supply upstairs, and moving the t-stat to the second floor would make a big difference. (the same goes for having ceiling level returns upstairs)

--->I haven't seen the system, nor am i knowledgeable for flex duct systems, so i recommend taking this with a grain of salt.

 

Thanks for your reply. I know the system says 3.0tons but the contractor sayid that it can provide 3.5 tons and I remember reading somewhere that that proves true. I just can't remember where I read that.

As for the return, I got 7 quotes (don't ask why ) where everyone said they would have to put the return where it is now because the ceiling in the upstairs is not big enough for the return. And with those 7 quotes 2 of them did a load calc and they both said a 3-3.5 ton system was needed.

I am going to have him move the tstat upstairs but is there any way for him to supply more to the upstairs registers and less to the downstairs by tuning the air handler or do I have to play with the registers manually?

 

I have a cape with the return in exactly the same location. When we purchased the house I also had inadequate cooling upstairs. The fix was pretty simple. I added 2 more supplies, 1 in each bedroom upstairs, then simply throttled the trunks in the first floor down. Now on 90 deg. days I have a temp difference of 2-4 degrees. At night the 2nd floor cools off nicely (our master is upstairs) and the house basically equalizes. T-stat for cooling is upstairs in the master.

You need more airflow upstairs, call the contractor back and have him add more supply for upstairs cooling.

 

Was the load calculation room by room or for the entire house?

Room by room results tell you how much cooling each area needs - the entire duct system gets designed based on that. In your case, you have a little more cooling on the main floor than the second floor.

If you move the t-stat upstairs without altering the ducting, the main floor will freeze.

Also with returns, the solution is to have several smaller returns at ceiling level rather than one large one. (more work for the contractor)

-----
One thing that I didn't mention is that for hot air to rise or cool air to fall, there has to be a temperature differential to begin with. If each room was getting the right amount of cooling to begin with, you wouldn't have a problem with warm air rising up, and having ceiling level returns would be less important.

 

Edit: I'm not too familiar with cape houses -> what's the second story like? (same square footage as first floor with pitched ceilings?, lower square footage with flat ceilings?)

 

capes are like this muggle... The upstairs is basically an attic... Usually 2 bedrooms down and upstairs unfinished. Then the homeowners add insulation and knee walls..

Usually made into two bedrooms. Go up the stairs and one left and one right. Plus a small dormer out the back for a bathroom...


Some have soffit vents, some do not. All have gable vents. Always cold in winter and hot in the summer...




Here is the upstairs gutted ( shows a window dormer. Dont think the OP has that.......... The op's unit ( a/c) is behind a knee wall I believe...





[ATTACH=CONFIG]32574[/ATTACH]

 

No returns in bathroom and kitchens law, but yes there should have been a return in each room for sure. Once you close the doors to those rooms at night, you're going to get even less supply air in those rooms.

 

Yah, sounds tricky to condition the second floor properly, and probably not much space for insulation.

If modifying the supplies/returns or balancing isn't enough, zoning may be an option to look into -> i looked up the model number and it's a two-stage, so might be a good candidate. Zoning should be a last resort and must be done right or not at all.

 

I finally got the thermostat relocated to the upstairs of my house. Unfortunately, it didn't do ANYTHING.

The electrician came and moved the thermostat around 8:30 this morning. When he completed the install, the temp upstairs was 80 degrees so I put the thermostat on 77 degrees thinking that it would be about a 4-5 degree difference between up and down. I left for work while my wife was home and about 2 hours later my wife calls me and said that the downstairs is freezing. I logged into the nest and see that the thermostat was reading 88 degrees.

In a nutshell, the upstairs got all the way up to 92 degrees with the AC running ALL day. It did not cool it down at all.

I contacted the installer and told him what was going on as this is just crazy since i spent so much money and the upstairs is 20 degrees hotter than the downstairs. He told me that he is coming tomorrow to adjust the dampers upstairs so there is more cool air coming out up stairs. Is this even possible?

At this point I am not even sure if the problem is with the AC install. I think it might be a ventilation issue with my attic as I do not have an fans sucking the hot air out upstairs. I just have gable vents (no fans). I purchased 1 solar powered gable fan but I am waiting on a friend of mine who is a contractor to install the fan.

Any suggestions as to what I should do? Do you think adjusting the dampers for more airflow is a waste of time?

 

Like I said previously, I have the exact same set up as you, even the gable vents.
There should be dampers on every trunk line. They need to be throttled to allow more air flow upstairs. On a 90 degree day I can maintain mid to upper 70's upstairs and low 70's down stairs.
At night the house equalizes with upstairs where our bedroom is cooling off nicely.

 

I have a two story house and experienced the same issue. The return and thermo are downstair.

What I did was similar to post #4. I partially closed some of the dampers to control the effect on the thermometer and push the cold air from the upstair vent stronger.

lawrosa is right. Do not install Solar Gable Fans. They are a waste of money. I bought two from Costco and there were like $300 each. I eventually replaced them with electrical ones ($115 each). The problem with Solar Gable Fans too weak and then they shut off at 5-6pm which is when the intense heat goes into my attic.