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Old 05-10-2013, 08:53 AM   #1
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Seeking advice on replacing A/C


Hi all,
Iím starting to get estimates for a new A/C for my 2 story, 3 Bed, 2K sq ft house, which is 15 years old. The current A/C is 3.5T, 42K BTU York. My biggest problem is that our upstairs is significantly hotter than the downstairs. Itís unbearable during summer months. After my initial estimate, the sales rep is saying that I should replace the furnace along with the A/C. Heís suggesting a dual stage furnace with variable speed blower, and a dual stage SEER 17, 4T A/C. He said that should resolve the problem of the upstairs being so much hotter. Iím really not looking to replace the furnace because we donít have any problems with heat, never cold in our house. But heís saying to put a new A/C with an old furnace is counter intuitive and we wouldnít see a difference. He also said we canít do a dual stage A/C with a single stage furnace. Is this guy blowing smoke and just trying to upsell me, or is there some truth to replacing both the furnace and A/C at the same time? Again, my biggest concern is the upstairs being a lot hotter than the downstairs. I appreciate your input and suggestions.

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Old 05-10-2013, 09:06 AM   #2
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Seeking advice on replacing A/C


Heat rises so a ceiling fan to push it down helps, other wise you need another system with ducts for upstairs or possibly more return air ducting upstairs. A competent contractor should be able to look at your ductwork to see if that is possible.

He is on a commission and trying to upsell you to pad his wallet. You need to do a proper heat load calc to properly size the unit. A 2 stage AC is good in very humid climates because it runs longer and removes more humidity. You need an extra fan speed and wiring and the circuit board may not be compatible. There are newer furnaces with ECM Variable speed motor fans which save electricity and work well with 2 stage units. Get some more quotes. Check this site for a reasonable DIY load calc. well worth the $$. DO NOT buy one w/o it.
http://www.hvaccomputer.com/gtarget1...Fe4-MgodPF4AoQ

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Old 05-10-2013, 09:49 AM   #3
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Seeking advice on replacing A/C


I asked him about J load calc and air flow upstairs and he didn't even turn on the A/C to see how it was running. This is why I'm having at least 5 quotes done. I did mention zoning or putting dampers, but he said he could only estimate the cost. The fact that the only "equipment" he had was his laptop kinda turned me off.

What can I expect from a competent estimate? Would they do a J load and duct leakage test on the spot?
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Old 05-10-2013, 10:30 AM   #4
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Seeking advice on replacing A/C


The heat load they should do. I have not heard of anyone doing duct leakage tests as sales people are just that. Air balancing companies that do ductwork etc may do it but you have to hire them. I have done zoning and IMO unless the ductwork is properly sized and setup right from day one (designed) then it is quite difficult and does not work well. The newer high end furnaces with ECM motors/variable speed fans can handle zoning better but there is always the problem when several zones shut and then where do you release the extra pressure. The old school systems with barometric bypass pipes IMO are crude and hard to setup and not what I would want but that was B4 we had ECM motors. 2 stage ACs work well with zoning and a ECM as you can shut a couple zones and on single stage not freezup the coil etc. Now you are looking at about a $12000-16000 pkg and I have done them. 2stage AC plus high end furnace with ECM motor plus a zoning panel system. Lennox has the Harmony 3 which you can look at their website. Still need decent sized ducts and trunks etc.
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Old 05-10-2013, 10:38 AM   #5
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Seeking advice on replacing A/C


I'd like to know what would best fix my problem with the upstairs being hot.

1) Zone the house, which would be adding dampers to some ducts, and replacing the A/C, not the furnace?

2) Replacing the A/C and Furnace with variable speed motor? No zoning.

I really don't care about efficiency or saving $ on utilility bills. They aren't that high to begin with. My biggest concern is comfort on the 2nd floor, esp bc my wife and I are expecting, and the nursery is south facing, so it gets really hot in there, even with ceiling fans.
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Old 05-10-2013, 10:47 AM   #6
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Seeking advice on replacing A/C


as yuri said, start with a manual j/heat load. from there you can determine if you want two individual systems or zoned. two systems, one for upstairs and one for down, would be what I would do in my own house. zones, when functioning properly, are very good solutions but functioning properly is downside.

I had to replace a two zone board this morning (no power to one stat, zone 2) and am always dealing with stuck dampers and transformers on those things.

listen to yuri. good luck.
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Old 05-10-2013, 11:02 AM   #7
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Seeking advice on replacing A/C


Quote:
Originally Posted by g_money View Post
I'd like to know what would best fix my problem with the upstairs being hot.

1) Zone the house, which would be adding dampers to some ducts, and replacing the A/C, not the furnace? Not likely it will work properly as you would need a bypass duct to release the excess pressure and that takes up space and is hard to setup or work properly. Can cause air whistling/ AC coil freezeup if it does not work properly. A ECM motor can slow down some to compensate but not a lot.

2) Replacing the A/C and Furnace with variable speed motor? No zoning. Might work better as a ECM motor is stronger and you can run it continuos for circulation. A 2 stage AC will dehumidify better and be more comfy. Adding more return ductwork if possible will help.

I really don't care about efficiency or saving $ on utilility bills. They aren't that high to begin with. My biggest concern is comfort on the 2nd floor, esp bc my wife and I are expecting, and the nursery is south facing, so it gets really hot in there, even with ceiling fans.
I have seen houses where they added a ductless minisplit AC ( high quality one like a Fujitsu) at the top of the stairs and they are incredibly quiet and that is the ultimate solution. Depends if they have a place outside for it and the piping etc. Google ductless minisplit air conditioner.

W/O seeing your house etc we cannot be sure what is best but now you got some better ideas.
http://www.fujitsugeneral.com/wallmounted9-12RL.htm
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Old 05-10-2013, 05:25 PM   #8
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Seeking advice on replacing A/C


Is the AC working now? If it has life left in it, maybe just get the ducts fixed. You may just need to install some dampers and adjust them for the season. Is there a return on the second floor by the way?

What area of the country are you in?

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Old 05-14-2013, 10:58 AM   #9
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I'm in NJ, so we have very humid summers. Is a 2 stage A/C unit really necessary? I just need the air flow increased upstairs, so should I get a better furnace with ECM motor and a single stage AC? Here are 2 quotes I was given, both Rheem products

1) Prestige RGFG-09EZCM 95% efficient furnace paired with Prestige RARL-048 JEC, 2 stage 16 SEER, 4 Ton

2) classic RGRM-10 ZAJS 95% efficient furnace paired with Value 14AJM42A01, single stage, 14 SEER, 3.5 Ton
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Old 05-14-2013, 11:18 AM   #10
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Seeking advice on replacing A/C


I'm in NJ, so we have very humid summers. Is a 2 stage A/C unit really necessary? I just need the air flow increased upstairs, so should I get a better furnace with ECM motor and a single stage AC? Here are 2 quotes I was given, both Rheem products

1) Prestige RGFG-09EZCM 95% efficient furnace paired with Prestige RARL-048 JEC, 2 stage 16 SEER, 4 Ton

2) classic RGRM-10 ZAJS 95% efficient furnace paired with Value 14AJM42A01, single stage, 14 SEER, 3.5 Ton
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Old 05-14-2013, 11:50 AM   #11
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Seeking advice on replacing A/C


If humidity is an issue then the 2 stage (#1) pkg. would be much better. May actually save you some $$ as once the humidity drops you will feel more comfy and can set it 1-2 deg F higher to feel the same as a 1 stage which you have to set lower to get the humidity down and runs longer to do that. Rheem makes some pretty decent value for the $$ units. I put a 2 stage Rheem furnace in my sister's house last yr. Their circuit boards are VERY well built and reliable. The Prestige furnace is a modulating furnace that I don't like as it is extremely complicated and hard to fix. I would go with their Classic furnace that has the ECM motor and the 2 stage AC unit. RGRM or RGTM furnace.
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Last edited by yuri; 05-14-2013 at 04:14 PM.
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Old 05-14-2013, 03:22 PM   #12
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Seeking advice on replacing A/C


Quote:
Originally Posted by g_money View Post
I'm in NJ, so we have very humid summers. Is a 2 stage A/C unit really necessary? I just need the air flow increased upstairs, so should I get a better furnace with ECM motor and a single stage AC? Here are 2 quotes I was given, both Rheem products

1) Prestige RGFG-09EZCM 95% efficient furnace paired with Prestige RARL-048 JEC, 2 stage 16 SEER, 4 Ton

2) classic RGRM-10 ZAJS 95% efficient furnace paired with Value 14AJM42A01, single stage, 14 SEER, 3.5 Ton
Any furnace that increases your air flow upstairs, will also increase your air flow downstairs.

Your duct system is not sized correctly. No matter which system you get, you may want balancing dampers installed so you get better air flow upstairs.

A 2 stage A/C connected to a single stage furnace with a standard PSC blower won't improve anything in your home's comfort.
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Old 05-14-2013, 07:16 PM   #13
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Seeking advice on replacing A/C


Can you use the registers to balance air flow?
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Old 05-14-2013, 09:04 PM   #14
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Seeking advice on replacing A/C


A second system is your best bet.
The duct going upstairs can only handle so much air if the furnace has a v-drive or not. To check if zoning will help close the registers downstairs and see if a lot more air comes out of the upstairs registers. If does not then the branch feeding it is already maxed out.
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Old 05-14-2013, 09:12 PM   #15
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Seeking advice on replacing A/C


Quote:
Originally Posted by Marty S. View Post
A second system is your best bet.
The duct going upstairs can only handle so much air if the furnace has a v-drive or not. To check if zoning will help close the registers downstairs and see if a lot more air comes out of the upstairs registers. If does not then the branch feeding it is already maxed out.
GOOD Advice from Marty. Sometimes a V drive will help but it is no magic fix/cure all for undersized or improper ductwork. I know it is frustrating trying to get a definite answer but a few of us Pros if we were at the house could easily determine that but we cannot be there. My suggestion of an additional ductless minisplit is pretty well foolproof but you would need to do more research and get quotes. Like asking a "internet" doctor for a definite answer, he needs to see you and do some tests. Same with the HVAC biz.

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