Using 3 ton unit to cool 600 sq ft room - Is it possible?

[JBonham27]

Before you think I'm crazy, listen to my scenario. I have a 1200 sq ft downstairs and there is a 600 sq ft addition above the carport (only upstairs area). I have one 3 ton unit for the entire house and upstairs is 20+ degrees hotter in the summer. I have to replace my downstairs unit because I don't have a heat pump and I'm heating my house on heating strips resulting in $500+ power bills in the winter. Someone suggested possibly taking the unit I am replacing and having it moved to cool the upstairs during the summer since it still works fine. I know it is important to properly size the unit for the area it is cooling because of moisture issues. He mentioned that it would probably work if you were to only use it during the summer and not drop it too low - no lower than 75, 76. He also mentioned a humidistat.

After having 5 technicians out, the concensus is that the ideal solution is to add a separate unit upstairs. I can't afford to replace my downstairs and install a new unit upstairs but I could probably afford this solution if it would work. Thoughts? Or is this a terrible idea?

I live in Savannah, Ga by the way.

[simplyrollin]

Its an awful idea.

[Shophound]

You will have humidity control problems with that much tonnage for 600 square feet.

Reduce the heat gain to the upstairs portions of the house is the best long term approach to your problem. Radiant barrier, added attic insulation, airtight seal at the ceiling plane (I think ceilings should be respelled as "sealings")...you may want to consider an energy audit by a competent outfit so you can derive a long term blueprint for turning your comfort and energy problems around.

[heaterman]

Multi stage new heat pump and zone control for the system the way it is now?

[JBonham27]

So I guess this isn't an option. I've brought up zoning to everyone that has come out and pretty much all of them have said you could but it wouldn't be practical in this situation and have pretty much shot it down.

My main issue is not enough air flow to the upstairs. I have well insulated attic. The suggestions (without adding separate unit) have been duct fan, modifying supply duct that runs to addition to start bigger (currently a 10 all the way), and upgrading main unit to 3.5 ton with some combination of the previous suggestions. There is probably 60 ft or more of duct from the unit to the upstairs supply vents along with sharp turns. I do have a return upstairs but that may need to be modified as well.

[Shophound]

To experience 20 degrees hotter upstairs than downstairs means you have some serious heat gain occurring in your house via some means. This is why I suggested an energy audit...your building shell isn't adequately protecting you from extremes in weather. When it does, your needs for heating and cooling go way down, almost to the point where ventilation and humidity control are more important than maintaining a comfortable room temperature (key word: almost).

If the upstairs 600 square feet is fairly open, you might consider a mini-split a/c up there instead of trying to tap into your downstairs system (which is never an adequate solution - upstairs and downstairs in a multi-story house are two separate climates).

[JBonham27]

To experience 20 degrees hotter upstairs than downstairs means you have some serious heat gain occurring in your house via some means. This is why I suggested an energy audit...your building shell isn't adequately protecting you from extremes in weather. When it does, your needs for heating and cooling go way down, almost to the point where ventilation and humidity control are more important than maintaining a comfortable room temperature (key word: almost).

If the upstairs 600 square feet is fairly open, you might consider a mini-split a/c up there instead of trying to tap into your downstairs system (which is never an adequate solution - upstairs and downstairs in a multi-story house are two separate climates).

Yes, I know it is not ideal to tap into downstairs but to buy a separate unit for one room upstairs just is not settling well with me. I also don't plan to live in this house for more than a couple years and do not think I'd get back what I'd put into adding a separate unit. I have brought up the minisplit and they all have said its possible but don't see a a great place to mount it. The upstairs bedroom has 6 windows - basically covering all of the exterior wall space.

How do I go about setting up an energy audit and what would I do with the results?
Thanks.

[big sky hvac]

I would consider a ductless mini split heat pump, as was stated earlier. They do make cassette units that mount in the ceiling, instead of on the wall. I know LG makes one, I'm sure there are others that do as well. I know you don't want to add a seperate unit because you don't see yourself staying in the home too long. If you have the money to invest in a mini split, you'll accomplish two things. You'll be able to enjoy the space with comfort and it will make a great selling point to a potential buyer when you do sell.

[jodybhvac]

Replace the downstairs, and get a window unit for upstairs. Window units are cheap and if it seems to do the job, upgrade when possible to a mini split. First, get the energy audit. Check with your electric company, some will do this for free.

[energy star]

Close the windows, install a reflective shield in attic and insulation. It's not the equipment size.

[JBonham27]

Close the windows, install a reflective shield in attic and insulation. It's not the equipment size.

There is hardly any air whatsoever coming out of the upstairs supply vents when the AC is on.

[Rheem29]

Just get a heat pump you live in the perfect area for it.

[JBonham27]

Just get a heat pump you live in the perfect area for it.

I've already decided to do that. What about cooling the upstairs? Any suggestions on that?

Thanks for the advice - having GA Power come out to do a free energy audit.

[jodybhvac]

When you have a new unit installed downstairs any competent installer will adjust the duct size to your needs. How big is your return? Where is your return located ?

[JBonham27]

When you have a new unit installed downstairs any competent installer will adjust the duct size to your needs. How big is your return? Where is your return located ?

The upstairs return is located near the floor and i want to say is an 8 inch duct. Not sure if thats what you were asking for. I've mentioned having the return in the ceiling and everyone says that won't matter.

[jodybhvac]

The return size may be a large part of your problem. I would have at least a 10in. return with a 20 x 20 grill. Are your supply vents near the exterior walls, preferably windows? If not that is the best place for your vents.If this is all re-done correctly , you may not even need a little window unit.

[JBonham27]

The return size may be a large part of your problem. I would have at least a 10in. return with a 20 x 20 grill. Are your supply vents near the exterior walls, preferably windows? If not that is the best place for your vents.If this is all re-done correctly , you may not even need a little window unit.

I'll have to check the grill when i get home but i want to say its 14x20 and i'll double check the duct size as well. Yes, I have concave ceiling (not sure if thats what its called) so the vents are close to the walls and there's only 2 of them in the bedroom itself located above the bed. The other 2 supply vents are in the bathroom and closet.

[Tommy1010]

Just some clarifying here.

You had only a 1st floor of 1200sq ft. with a 3 ton unit. ?
You added an upstairs area above your carport. And thats your only upstairs area?

Is that your (now) bedroom you were refering too? with all the dam windows in it? lol

How was it ducted if you have an attic? Im trying to picture this.

Is the room basically next to attic, next to unit? how were the ducts put in ceiling? And you only have 8" return? Thats probably why you dont feel air flow through the vents.

If theres a door, is it hard to open after its closed? depending on your supply size, probably positive pressure issues.

Or aMi CONFUSED and theres no ductwork to it at all?

[JBonham27]

Just some clarifying here.

You had only a 1st floor of 1200sq ft. with a 3 ton unit. ?
You added an upstairs area above your carport. And thats your only upstairs area?

Is that your (now) bedroom you were refering too? with all the dam windows in it? lol

How was it ducted if you have an attic? Im trying to picture this.

Is the room basically next to attic, next to unit? how were the ducts put in ceiling? And you only have 8" return? Thats probably why you dont feel air flow through the vents.

If theres a door, is it hard to open after its closed? depending on your supply size, probably positive pressure issues.

Or aMi CONFUSED and theres no ductwork to it at all?

I bought the house last summer. The addition was done in 1998. Looks like the outdoor unit was replaced in 2005 (no heat pump - no clue why unless it was previously gas heat).

Yes - downstairs is 1200 sq ft with its own attic.
The addition is above the carpart and is my master bedroom with all the 'dam' windows and is the only upstairs area (not directly above the main part of house).

The duct work to get to the addition is interesting and probably hard for me to explain. The floor of the addition is next to the attic above the main level. The duct passes from the main attic to the addition attic through the back side of the house and above the stairwell that leads up to the addition. The rest of the addition attic is well above the downstairs attic. That may not make sense but the addition attic goes down above the stairs and that is the only place that the attics meet.

I believe the return duct is an 8 but i will have to double check when i get home. The door is not hard to open or shut. It is a very interesting setup and is my first home. I'm surprised the inspector didn't notice anything unusual. Won't be using him again.

[JBonham27]

And yes it is all being run off one 3 ton unit downstairs and on the opposite side of the house as the addition. And to be clear, the addition is the only part of the house that is upstairs. I cant tell how old the air handler is because the cover has rusted off. Looks very old but the outdoor unit is from 2005. Very strange.