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rheem ac a-coil replacement question
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Posted by jmcqueen (My Page) on Tue, Jan 13, 09 at 4:24
| hi all:
i have been reading this forum with much enjoyment and have the following to run by the pro's. i have a 15 yr old rheem criterion 75k btu gas furnace and a 2.5T? rheem AC coil (Red-T-Coil), model RTB25ACU. assuming this means 2.5 ton??? here's the prob. i get good airflow from the furnace during the winter and my house is fairly evenly heated, but in the summer, the most pull-down i can get vs. the outside temp is 13 degrees. so, when it's 90 outside, it's a balmy 77 degrees inside the house. the AC won't turn off all day...and for most of the night. i have had our local AC guy out a couple of times and everything appears to be in order with the AC. no leaks, pressures check ok, etc... a couple of seasons ago, the tech did have to add some R22 when he discovered a small leak, which he also fixed. so....
i suspect that i simply have an undersized AC unit for my house. here's what my idea is, and tell me if this is even do-able and/or advisable. i am looking at bumping up the a-coil to a 3.0T or 3.5T (like a carrier CNRPV). would i be ok doing this without changing the compressor out? i suspect that the coil i have is just a piece of garbage based upon what i've read, but i don't want to spring for a $400 coil if what i am considering doing is just out of the question.
any advice/help would be greatly appreciated.
thx,
j |
Follow-Up Postings:
RE: rheem ac a-coil replacement question
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That evaporator coil is a 2 ton coil. Do not mismatch the evaporator coil and the condenser coil. Besides mismatching size, you will end up mismatching the energy efficiency rating. That coil is what's called a 10 Seer coil, and nobody makes a 10 Seer coil anymore. The lowest you can go is a 13 Seer system. I would go ahead and do everything right the first time, that way you will not have any issues with mismatching the system.
Also, if you get a free estimate from someone, see if they can do a manual J load calculation on your house to make sure the unit is not undersized.
A very rough way of figuring out whether you unit is big enough is taking the square footage of your house dividing that number by 600. That will be a somewhat close estimate to what size unit you need.
Performing a manual J load calculation is much better because they account for the windows, doors, insulation, and position of the house.
Hope this helps. |
RE: rheem ac a-coil replacement question
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| tlewis: thanks much! home is 2200 sq.ft. west-facing, colonial two-story which, at first glance based upon the formula you have mentioned, would put me at 3.66T. we live in the midwest (ohio) and have roughly a 5 month cooling season, so it's pretty important that the new unit be sized properly. i will check into getting a load calc done to be sure, but can i firmly conclude that 2.0T is just way too small? like i said, the furnace does a great job keeping up on cold days, so at least i know my system has the capacity in terms of air flow. |
RE: rheem ac a-coil replacement question
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| Can't confirm a system is too small without a load calculation done, but 2 tons does sound small for your size home. Increasing the coil size won't make the 2 ton cool better. If anything it will decrease its ability to remove moisture because it will run warmer. I wouldn't mismatch the coils, either. You're probably better off with a new properly-sized A/C system. |
RE: rheem ac a-coil replacement question
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| thanks for the pointers ryan. i am thinking about biting the bullet next spring. i did some checking online and saw a Carrier 3 ton 12 - 13 SEER R410A cased coil and a Bryant condensor (supposedly a matched setup) for $1500 (on e-bay). I will probably be in the house another 6 years or so, but don't want to buy crap. service tech changed the board and blower in the furnace last year and it runs just fine. just need a decent unit to make my house cold. any recommendations on a condensor/coil...with the consideration that the furnace might puke out within the next 5 or 6 years? i did a pretty close load calc using some online resources and came up with 3.49 ton needed for my house. i didn't fudge too many numbers... |
RE: rheem ac a-coil replacement question
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| The problem is going to be moving almost twice as much air through (supposedly) 2 tons worth of ductwork, assuming it was sized right to begin with. I would not trust an online load calculation. You want an ACCA-approved Manual J load calculation done by a professional, then your ductwork inspected to see what needs to be done. That would be the best way to do it. Good luck. |
RE: rheem ac a-coil replacement question
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| please pardon my lack of understanding. i think i'm finally getting it though. are you saying that because i would be increasing the tonnage of the AC by 50% (from 2T to 3T as in the above example), that i need to assure that the air flow and ducting is sufficient? many thanks,
j |
RE: rheem ac a-coil replacement question
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| J, you got it. Without sufficient ductwork, your new system won't deliver the expected performance and capacity, and may not be much better than what you have now. I haven't seen your ductwork, though; I'm just stressing the importance of a professional evaluating your whole system and doing a load calculation to determine sizing, then making certain the new system will work with what you have now. Good luck in getting this taken care of. |
RE: rheem ac a-coil replacement question
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| thanks much. i will keep this in mind. j |
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