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Old 07-28-2012, 01:23 AM   #1
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Hello, band New to forum so go easy on my ignorance of the subject. I'm a student and purchased an older house 2 story built in 1979. Not much of an attic but the hvac is up there. My house is based on a square. Bedroom in each corner upstairs with the stairs and landing in middle. Thermostat is up stairs in middle of house below the attic stairs. My house is cold while my thermostat thinks it's not. I added a vent to this area to alleviate our calibrate it a little but it's not helping as much as I would hope. My ac guy just cleaned my coils and after explaining all this he said my ac is 4 ton and my return is 16 inch. He said 20 inch is minimum on a4 ton.

I am in the process of drawing out some schematics to move the hvac behind the thermostat and in the house. Unlimited return and cooler unit means it will save power. Only downfall being between all 4 bedrooms it might've a little noisy. I can live with that. Beck I'll triple the Sherlock around the unit to help our use hardy backer x3.


The area would take up one of my rooms closets which is fine it's only 9x10 for office any way but what is a logical price for a move like this? Hvac plentium goes downstairs where I want to install the Hvac with plenty of room. I can take pictures or video. Just need more ideas.

I'm a handy man, I learn from tearing apart.

Edit also I want to replace all duct work in walls it's really bad from pure owners with no filter. Not easy to do without pulling out sheetrock. Any suggestions or tricks?
Thanks
Mike


Last edited by ang1dust; 07-28-2012 at 01:30 AM.
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Old 07-28-2012, 05:31 AM   #2
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There is no way to give any realistic pricing on an internet forum. Prices vary widely between different regions, and even within the same city at times.

Call around to friends and neighbors for recommendations for contractors. Get several estimates (and please don't just take the cheapest one based solely on price). Do your homework - don't rely solely on "internet reviews", which are quite often bogus junk put together by someone who has never met the contractor.

While it's good to educate yourself, I'd caution you against trying to engineer the job yourself. Duct design in an existing home can be very difficult even for experienced contractors, and it's best to leave something like that to the professionals.

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Old 07-28-2012, 09:11 PM   #3
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4 ton would require 1600 cfm. that is base off the standard 400 cfm per ton. there are some situations where 350 per ton is more ideal (more humidity removal)16" is real close to the right air flow for 4 ton even based on 400 per ton.16" flex will carry just under 1500 cfm. 18 " would be a plenty carring 2000 cfm. 20" is overkill @ over 2500 cfm.

if you have a non digital thermostat I would considering changing to a quality digital one. I personally like Honeywell tstats. A digital tstat will give you a temp swing of less than one degree. many old non digital have 3 or more degree swings.

I have done some extensive testing for a fairly picky customer. when a properly installed system is running and just before the tstat will satisfy all rooms would be right at set point. when the unit would turn off (during the off cycle) rooms will increase in temp before the tstat does. this is typically 1 to 3 degrees before the tstat drops one degree to bring on the cooling. I have since tested this many time which leads me to the statement that at any given time any room on a system should be within 3 degrees of set point and most times 2. this is with tstats with less than 1 degree differential. If a tstat has a higher diff then this will be more.
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Old 07-29-2012, 03:40 PM   #4
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Mike,
The comments made on duct sizing are based on a target "static pressure", which is a pressure that engineers shoot for when designing duct systems. Before you go to all this trouble (and expense!) I hope you will consider a few things:
1) It would be an easy thing to add more return to your system by cutting in an additional return in the ceiling somewhere on the top floor.
2) If your top floor ducts are in the attic, and will remain in the attic, then you are not gaining anything by moving the air handler down into the house. The air still has to go through those ducts (in the hot attic).
3) There are wireless thermostats availiable that would allow you to move the thermostat to a better location, without having to pull a new wire. You could install one of these yourself.
4) Have a duct cleaning company come in and clean your ducts! WAY cheaper than what you are talking about doing! They can even show you before and after pictures so you know it was done right.
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Old 08-01-2012, 01:12 AM   #5
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This is all great info thanks for the feed back.As for the price quote, I figured that was far fetched but I the it in there. My air ducts are horrible, plentium is gross, return box is filthy and my return seems from my ac guy and you all to be mild to slightly under sized.

Moving the hvac down to house level (still on second floor) feels like the best idea. I realize my air control ducts are in the attic but I have no return duct (witch is currently about 30 feet long) to increase my return air temp but my return amount becomes nearly unlimited. Can an hvac return be to much? Should it be restricted to 400/ton? Not to mention my hvac will be 10-30 degree cooler year round. 3 positives for moving it right?

Lastly I have a hunter digital thermostat. I had a thermostat from home depot with the manual wheel on the side, I found to be half my problem because the air enters the thermostat from the rear, meaning the 8th inch gap between the tstat and the wall was all it had in determining the temp. The hunter was a big upgrade but did not fix my issue.

My main concerns are 1 help moving the unit with a professional, tips etc since I am pretty set on moving it unless someone can give me something other than expense as a negative

2 replacing hard to reach ductwork downstairs

3 what precautions can I take for downstairs duct work to make it easy to replace in 15 years?

Edit: I read maximum quality comfort has a return in every room? Comments? Remember I have an older house, rooms are 8 foot high and range from 9x10 - 18x28 rooms. Just under 2k sf

I'll take a video of what I have and add the link this weekend so you can see what I'm talking about.

Last edited by ang1dust; 08-01-2012 at 01:36 AM.
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Old 08-01-2012, 05:08 AM   #6
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Quote:
but I have no return duct (witch is currently about 30 feet long) to increase my return air temp but my return amount becomes nearly unlimited. Can an hvac return be to much? Should it be restricted to 400/ton?
The goal of a return is to pull air from the areas that need conditioning, and in general it's best if that return is either (a) centrally located or (b) installed in such a way that it draws from EVERY conditioned space (i.e. each room). However, since we really don't know what sort of setup you have it's impossible to give advice like that.

IMO you're talking yourself into work that is unnecessary, but if you're willing to spend the money then I'm sure you can find someone who'll take if from ya

Thermostats don't need "air space" to sense temperature. Older ones sense temp through a bimetal coil, newer digital ones use thermistors or some other electronic means.

I'm not sure what you mean by "precautions". You're not going to be working with the downstairs ductwork - are you? If not, then there's nothing to do ...
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Old 08-01-2012, 06:39 AM   #7
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I want to replace ALL ductwork as stated in my second response because it's filthy. Previous owner ran it without a filter for quite some time and from what I could tell it was not the first time. As to the thermometer, it was the only opening to sense temp, I don't see how it could otherwise. With the night and day difference of stats I think it was the right choice. I want precautions I can take to ensure a smooth replacement of downstairs ducts 15 years from now otherwise I'm tearing down sheetrock to get to them-which I will do this time but I'd rather add something this time to make it easier next. Help
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Old 08-01-2012, 07:17 AM   #8
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I still don't quite follow you. If you replace all the ducts, seal them properly, filter the air correctly, and perform regular maintenance on the system, then the chances of ever having to replace ductwork again would be very, very slim.

Even so, I wouldn't know of any "precautions" you could take that would help you to replace ducts (again) in the future - perhaps install hinged openings in the wall cavities to allow easier duct access?

Quote:
With the night and day difference of stats I think it was the right choice.
I'm not saying the old stat wasn't bad, I'm just saying there's not really a need to have any sort of a "gap" at the back of the stat in order for it to sense temperature - in fact, most tstat manufactureres recommend that you seal the rear of the stat to prevent any sort of heat gain from the wall.
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Old 08-01-2012, 07:45 AM   #9
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I still don't quite follow you. If you replace all the ducts, seal them properly, filter the air correctly, and perform regular maintenance on the system, then the chances of ever having to replace ductwork again would be very, very slim.

Even so, I wouldn't know of any "precautions" you could take that would help you to replace ducts (again) in the future - perhaps install hinged openings in the wall cavities to allow easier duct access?

Quote:
With the night and day difference of stats I think it was the right choice.
I'm not saying the old stat wasn't bad, I'm just saying there's not really a need to have any sort of a "gap" at the back of the stat in order for it to sense temperature - in fact, most tstat manufactureres recommend that you seal the rear of the stat to prevent any sort of heat gain from the wall.

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