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

[big sky hvac]

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.

So what you're saying is you have 1800 sq. ft. of living space with a 3 ton A/C? I guess it depends on the particulars, but seems a little oversized to me. I would suggest having a load calc done before purchasing any new equipment. I would also look into a heat pump as well, your climate is well suited for a heat pump.

[beshvac]

Inspectors don't know anything about duct, all they are hired to do is make sure its hooked up.

Without seeing your house nobody here can have a clue about your needs. You need to find a local contractor that knows what they are doing to do an onsite analysis.

If I came out to your house I would give you a quote to 100% solve your problems and it would not be cheap. Chances are from your post I would probably walk away. the reason is 100% solutions cost 100%. When you start talking about "if we just did this...." then 99 times out of a 100 "I thought it would work better than this?"....and its another "warranty call" to tell you that you should have took the big number. There are plenty of cheap contractors out there to give you partial solutions-look on craigslist.

[JBonham27]

Inspectors don't know anything about duct, all they are hired to do is make sure its hooked up.

Without seeing your house nobody here can have a clue about your needs. You need to find a local contractor that knows what they are doing to do an onsite analysis.

If I came out to your house I would give you a quote to 100% solve your problems and it would not be cheap. Chances are from your post I would probably walk away. the reason is 100% solutions cost 100%. When you start talking about "if we just did this...." then 99 times out of a 100 "I thought it would work better than this?"....and its another "warranty call" to tell you that you should have took the big number. There are plenty of cheap contractors out there to give you partial solutions-look on craigslist.

I simply posted a question - check the subject line. People started asking other things so i tried to fill them in. I've had more than 5 contractors come out and everyone of them has said something different so I have no clue who to believe or use. And ive heard quotes that are up to 8 grand different so I decided to go to the internet. Are you suggesting I go to the one that is 8 grand more because the cost is 100%. Give me a break. This is an HVAC forum so it seemed like as good a place as any to get some information.

And isn't that a contactor's job? To offer solutions. Or is there only one in every situation?

[beshvac]

I simply posted a question - check the subject line. People started asking other things so i tried to fill them in. I've had more than 5 contractors come out and everyone of them has said something different so I have no clue who to believe or use. And ive heard quotes that are up to 8 grand different so I decided to go to the internet. Are you suggesting I go to the one that is 8 grand more because the cost is 100%. Give me a break. This is an HVAC forum so it seemed like as good a place as any to get some information.

And isn't that a contactor's job? To offer solutions. Or is there only one in every situation?

Yes....but in a previous post you can't even describe the ductwork to the room.. You need a manual J calc to determine how much cfms are needed to be supplied to the room; Will 3 tons cool a tiny room?-YES Will it do it with comfort?-NO Will it do it efficiently?-NO of the contractors ho came out-who actually did a manual J? or would do one and prove their design?

[JBonham27]

Yes....but in a previous post you can't even describe the ductwork to the room.. You need a manual J calc to determine how much cfms are needed to be supplied to the room; Will 3 tons cool a tiny room?-YES Will it do it with comfort?-NO Will it do it efficiently?-NO of the contractors ho came out-who actually did a manual J? or would do one and prove their design?

Thanks for answering my question. No one did a manual J calculation. Guess I'll call a couple more.

[Hheating]

When it comes down to it there really is only one 100% solution. There are practices and methods for sizing ducts and equipment that are very specific. A contractor should be able to come into your home, take all the measurments, and tell you what the "right" way is to condition the house. That solution will be 100% and you will pay 100%. Any other solution is going to leave you less than 100% comfortable and be less efficient.

Between you and your contractor you have to find the balance between your budget and comfort needs. Just because there is only one correct solution for the home does not mean that it is necesarily right for you. Just know going in that your contractor can do whatever you want them too, as long as you know if may not be 100% correct

[tedkidd]

I don't think there is any such thing as a 100% solution. Kind of like reaching absolute zero.

Let us know the results of your audit?

Equipment sounds grossly oversized. This leads to short cycling, which means far areas never receive conditioning. Does your ac ever run continuously?

A mini split works great in small spaces, if duct constraints make one unit impractical.

Hopefully this free audit will give you an analysis and recommendations regarding the improvements you hope to make. Please share.

[JBonham27]

I don't think there is any such thing as a 100% solution. Kind of like reaching absolute zero.

Let us know the results of your audit?

Equipment sounds grossly oversized. This leads to short cycling, which means far areas never receive conditioning. Does your ac ever run continuously?

A mini split works great in small spaces, if duct constraints make one unit impractical.

Hopefully this free audit will give you an analysis and recommendations regarding the improvements you hope to make. Please share.

Have a guy from GA Power coming out at noon today for audit so I will let you know. Thanks.

[bfsman]

the best thing about doing a manual j calc is from that point every dollar spent to fix the problem is moving in the right direction no guessing you may find out a good result is not achievable do to limits on duct size then there are always other options

[sktn77a]

You could use your old 3 ton in the 600 sq ft room. It would certainly cool the room but it wouldn't dehumidify it very well. Also, because it's so oversized, you would have air basting from the vents. Finally, it wouldn't be very a efficient solution. This biggest downside to your proposal, though, is that it wouldn't be cheap - the labor (half the cost of a new install, at least) would be more than you would want to spend to have a half-baked solution to your problem. I'd go with the new HP downstairs and window units until you can afford a 1.5 ton split system or a minisplit.

[westval]

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.

Imagine walking into a house in July with a realator and finding the upstairs bedroom is 20 degrees hotter than the rest of the house. Would you buy it?

[ask_eddie]

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.

You have a couple choices Follow the advice of the 5 contractors that have seen the job or add supplemental air , as suggested a mini split or since it has so many windows add a window unit or a PTAC ( motel type unit )

[tedkidd]

You could use your old 3 ton in the 600 sq ft room. It would certainly cool the room but it wouldn't dehumidify it very well. Also, because it's so oversized, you would have air basting from the vents. Finally, it wouldn't be very a efficient solution. This biggest downside to your proposal, though, is that it wouldn't be cheap - the labor (half the cost of a new install, at least) would be more than you would want to spend to have a half-baked solution to your problem. I'd go with the new HP downstairs and window units until you can afford a 1.5 ton split system or a minisplit.

Well put. Only thing I'd add; expect mold, on the supply grilles at the very least. Next on books/paper, and possibly on walls.

In humid environments it is very important that moisture be removed as air is cooled. Cool it too fast and moisture removal can't keep up.

[beenthere]

Have current system replaced with a heat pump. Have contractor dispose of current system. Go to Wal Mart and buy a 4,000 or 5,000 BTU window A/C for that room above the car port. Money well spent, and money saved.

[mrushing]

call a pro

[ACFIXR]

Before you think I'm crazy, listen to my scenario. a terrible idea?

.

I just bid a job that is going to be 15 tons on 460 sq. ft. There is already 5 tons on it, I'm going to add 10 for redundancy.

[Mackie007]

As others have said...

Install two units.

Based on your description you have two separate buildings that are connected. The duct work that was added for the addition is clearly not working, fixing it will likely be more expensive than installing a separate mini-split on the addition.

So...

Install a properly sized heat pump in the original part of the home, sealing off the crippled duct work going to the new addition as part of the install. Then install a properly sized mini-split heat pump on the newer addition and call it done.

Best Regards,
Mac

[nismo1]

Unfortunatly sounds like the addition was done wrong to begin with. Heat gain and ducting problems. Energy audit will help determine heat gain problems. Has this problem always existed? 3 tons is way too big don't do it. If reducting isn't possible than seperate cooling source is nessasary ie window unit,ptac or mini split. Zoning won't help unless duct is corrected. Also if seperate unit is used than main unit size will need to be reduced less the 600sqft. Surely 5 techs can't all lack the ability to give good counsel. If the consensus is the same go with it.

[Starwarsith88HVAC]

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[catmanacman]

just guessing i would go with a 2 stage unit with zone control and a rehab of the duct system,will probably need a bypass damper . also if you knew how many people say they are moving in a year or 2 to still be there 5 years later .