Raised the heating fuct return

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We are finally replacing the HVAC in our house. The furnace is original in 1971, 140,000 BTU. Central air is 3 1/2 ton Trane put in 1987. The new ones will be both Trane units. The new furnace will be 92.5% AFUE 112,000 BTU. AC is the same tonnage at 15 SEER. The house is 2,100 sq ft in NJ.
The HVAC contractor suggested raising the duct returns on the second floor from the existing near floor locations to a higher location near the ceiling when I told him our second floor doesn't get cooled that well. The plan is to raise it without additional ducting by using the joist space. Does it make sense?
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yaofeng wrote:

it does and its simple. What effect will it have in the winter?
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Respectfully,


CL Gilbert
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I presume the hot air will be recycled back to the furnace inlet, which is not necassarily bad. The furnace just don't have to crank out as much heat working on heated air.
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What you will likely have is some pretty extreme stratification, where the elevated returns are, besides reduced heating efficiency.
At least if he put the discharges near the ceiling with the returns below, you'd have a manageable loop, just be overheating air at ceiling.
What I've found to work very well, for heating and cooling is plastic flow-diverters that magnetically attach to registers. E.g. instead of cooled air flowing across floor to return, diverter makes it ascend for a bit and mix with room air well above ankle-height. Much cheaper, and more effective, IMHO than raising return.
OTHO, if return and discharge were reversible summer-to-winter, you'd be in business.
HTH, J
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If the duct is extended, you have two outlets. Open one, close the other, depending on season. I've seen that done with good success.
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yaofeng wrote:

Did the contractor do a heat loss / heat gain calculation to come up with those sizes?
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No. This guys has his business in our town and has been in business for 35 years. He takes out about 1,000 permits a year. He did most of the houses in my neighborhood. Actually one of my neighbors gave me his number. He probably did the existing AC before I moved in the house in 1990. We have had a couple of estimates for replacing the system since late spring but kept procrastinating. His number is the lowest, although not by very much. What started it again was the AC condenser went kaput a week ago. The compressor heater went. He sent a gu to fixed it the same day coming to our house to give me the estimate.
In addition to pricing, I am prejudiced because I like him. He explains how things work to you.
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yaofeng wrote:

If he puts that many A/C systems in two story homes the design should have had them cooling both stories equitably!
I can explain to you how airconditioning systems work until hell freezes over, and it means nothing if I don't design the systems I install in two story homes to work properly for the occupants. I knew guys that had been in the HVAC business for many decades and didn't do much right; some keep doing it the way they had always done it and never learn to do it right!
Running the returns up the walls should help some; have top and bottom registers so you can close one off according to the season. (Use bottom return for heating.)
Every home should have a manual J heatgain done by someone that will do it right. You might be able to make some changes that would allow you to drop down a half or full ton in unit sizing. A lot of 3.5ton systems are only putting out 2 to 2.5-ton of cooling to the conditioned space.
For example I replied to this Tech: 35 ton 10 SEER system.
I'm at a loss for the 8 degree DT. HO has never said house doesn't cool well just runs quite a bit when above 88 deg. Coils, ductwork, blower, etc. checks OK. If I plug these numbers in my psychometric calculator (which by the way works very well) I get these numbers
<>Here are my readings.
Ambient Temp= 78
Suction PSI= 70
Suction Temp= 61
Head PSI= 225
Liq. Line temp= 104
Entering DB= 74
Entering WB= 64.5
Leaving DB= 66
Leaving WB= 61
3.5-Ton equipment yielding:
17203 "total Btu/hr" Not even a 1.5-ton
13306 Btu/hr Sensible.
3717 Btu/hr Latent What is up? ----------------- The above tonnage loss is not as unusual as you would think; it is rather common but not quite to that extent! <>http://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html There is also probably a lot more wrong than just the charge and airflow. - udarrell - Darrell
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Factors in the Correct Sizing of Residential Air Conditioning Systems -
Recommended Procedures for Proper Duct Sizing of Residential Air Conditioning
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yaofeng wrote:

Don't let size or emotion drive your decision.
http://www.proctoreng.com/articles/bigger.html
The same scientific process should be used to size heating equipment. Ask your contractor if he'll do a "Manual J" load calculation prior to sizing and installation of the furnace and A/C. Tell him it is for your peace of mind if nothing else.
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Don't forget he is the low bid.
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If the guy chooses the wrong size unit for your house, "low bid" won't mean much to you a year or two from now. Travis is making a good suggestion.
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I am very biased in this matter as you will see if you haven't already.
This guy is an electrical engineer. I am also an engineer licensed to practice in New Jersey. We talk the same language even though in different disciplines. He has 35 years experience in this field. My experience is not much different. If you ask me to provide calculations for something I know the answer already I'll dismiss it as a waste of time. But if I must do it, I will. There are no fewer than four models similar to my house in the block. I trust his estimation. Further more, is he providing far larger capacity heating and AC unit than the previous rwo estimates? All three estimates were in the same size range. One estimate was by PSEG. Another indication is the size quoted in the estimates as compared to the current unit and is my current unit adequate? Except for the less than satisfactory AC on the second floor which he is providing a solution for we have no complaints. This is engineering. Not science. Could all three have made the same mistakes? I can not rule it out but it is not likely.
Call me pigheaded. One thing I am glad I am not in the medical profession is the defensive medicine and measures they have to put up in their daily work. Although they probably bring home much fatter bacon than I. Does experience not count anymore that one has to document and substantiate every thing he does? Does experience, trust, relationship and credibility not count in your profession? I can not say I will enjoy my work if I have to put up defensive medicine (measures) on a daily basis. No matter the amount of bacon I earn.
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Wait a minute.
You like him, you are prejudiced toward using him, your are both EE's.
But you come to a usenet forum asking people you don't know and never will know, if he knows what he is talking about?
You aren't pigheaded, you are two faced.
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I want to give you an opportunity to substantiate your accusation that I am two faced. Please tell me how and why I am two faced.
I obtained three bids. He not only came in the lowest, he has references from at least three of my neighbors. He is using similar size units as my existing ones which work and those he installed in the neighbohood which has houses built in the same era of similar living space. He has been in business in this town for 35 years. He explained to me how he intend to do it and as much as I could understand how things work. We talked in my kitchen. We found we both have engineering degrees and share comon intersts in cars and other hobbies. His kids grew up in the same school system as mine.
So how does that make me two faced if I use his service?
I am not an electrical engineer for your information.
And finally is that how you treat people in your daily encounter by calling them names?
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What he's saying is that if you trust the guy so much that you're willing to do all this typing, then why did you come here looking for other opinions, most of which you're arguing with?

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yaofeng wrote:

Why an engineer wouldn't want to get the facts of the matter and make a decision based thereupon is beyond me.
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If you are so trusting on his advice for the size of the unit, why are you asking the group for advice on his suggestion to raise the return air to the ceiling on the second floor????
Regardless, to answer your question, this is a fairly common practice, particularly in retro-fitting into an older home. That is as long as it meets the local code, and it is on an interior wall.

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mwlogs wrote:

Maybe I am bored?
I have no problems regarding his selection of either the furnace or AC. Two other prior estimate made the same selection. My neighbors all have similar size unit. Raising the return is something new to me, however. I still trust him. Does that mean I am not supposed to verify?
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yaofeng wrote:

Why bother? You're not verifying his sizing of the equipment.
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Why should I? Am I preparing for a litigation down the rood if the house is not heating or cooling to MY satisfaction?
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