HCAV Duct QUESTION


My home has an oil furnace. All rooms are supplied by 4" ducts fed into side wall registers. Each room has two sidewall registers supplied by 2 different 4" ducts. Cold air return is 3 large intakes at both ends of the house. None in the bedrooms. This is a small 1239 sq ft ranch house.
I have consulted to multiple HVAC contractors to determine if the ducts will need replaced or not if I add AC, Heat Pump, dual fuel, Geothermal etc. The answers I have received are across the board and I am not sure who is correct and who is not, who is a hack etc. One ran a manual J and said the ducts would be fine.
Some say that they will not need replaced.
One told me if I did not replace the 4" with 6" that they would sweat so much when using the air conditioning that they would cause much water to drip off them.
Some say that we will have to replace the 4" duct up to the 4" side wall boot with 6" ( I do not see how this is going to increase the airflow if you leave the end at the original 4". Would this not be the same as having the entire duct be 4". What good would this do.
Of course, I know that most with the exception of the bathroom and one vent in the living room could be replaced easily with floor vents and connected to the 6" ducts.
Any opinions would be appreciated.
LJ
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Old_Boat wrote:

Very nice of him, but the manual J would only be used to figure the size of the A/C unit, not the distribution system.
You need someone who is willing to do the proper calculations and as udarrell noted, also make sure the whole system will function properly.
--
Joseph Meehan

Dia \'s Muire duit
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If you send me a schematic drawing of your home, the existing duct system, which direction your home faces, the color of your siding and roof, what kind of window treatments you have, the placement size and construction of your windows, the insulation, if you have a basement (are the walls insulated or not, how much below grade, floor coverings etc, trees type size and placenment, what type of ductwork you currently have flex/metal type of insulation on or in it, etc. I will also need the town you live in and a Major town in your vicinity. I can perform a complete Manual J and D for you with duct and register placement. Asking this type of information on any news group is going to be futile. There will be nominal charge for this report, but with it you can begin to do some duct improvement prior to having any equipment installed. The only place I have ever seen a 4" duct is in a small bathroom. This is a nice report to have when dealing with any HVAC company. I charge 250 for a house under 3000 sf. If you would like it done we would get alot more information over the phone, because there are more factors that are needed to perform it right.
--
Bob Pietrangelo
snipped-for-privacy@comcast.net (home)
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Bob, that is an excellent price anyone should jump on. The peace of mind knowing someone did the correct evaluation and calculations is irreplacable. And that is the OP's quandry, who to believe.
LJ, knowing what size ducts you need is hard to say unless as Bob states, one knows all the room dimensions to determine the proper cubic feet per minute air flow. It's best to have someone like Bob do the evaluation and then you have something to judge contractors with.
If your ducts are only metal without insulation, or the insulation is old and 1"or less and the ducts run through unconditioned space like an attic or crawl space, they will sweat, loose cooling and heating thereby reducing the efficiency of the system. Once someone like Bob does your evaluation, you should also follow up and have them write up a set of specs that the eventual contractor will build to and you have to hold them to the specs. Don't trust anything by word of mouth like happened to me. I just built a new home and contracted with a contractor while living states away, to put in the A/C system. They did an ok job but they didn't put in rectangular ducts in my crawl space like I wanted and they agreed to do, therefore I have round ducts and I can't get under some of them. The insulation is 2" foil faced and they put it on so tight it's only about 3/4" thick, it sweats like crazy in the summer A/C months. I'm in the process of cutting all the insulation lengthwise along the ducts and adding a 4" strip of new insulation to allow the insulation to expand to it's 2 " thickness. In the parts I've finished, I measured a 4 degree difference in the outside temperature of the insulation between the thin insulation and what I've repaired. Moral, is, get everything spec'd out in writing and make sure they put it in according to the specs. Check the insulation and make sure when they are installing it that they aren't wrapping it too tight. It's hell fixing it afterwards and I tell myself everytime I go under the house to fix more of it. I'm about 2/3rds finished and pushing to get done before the A/C season comes.
Bottom line, get someone like Bob to Engineer it for you and then use that to hire the contractor and get the job done. In my estimation, most contractors are going to do an ok job but from what I've seen lately, without specs to go by, you are at their mercy. Also, if they do end up installing new flex duct, make sure they don't use flex duct for the main runs, have them put in metal duct and use flex duct to go off to each room. Minimize the length of the flex duct runs and make sure they are supported every 4-6 feet and the strap has a semicircular metal support on top it to hold the insulation up without crushing the insulation because if you don't, that flex duct will sweat everywhere there is a support strap and the insulation is compressed.
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I agree.
Send Bob the money today.
Also throw in a 20% gratuity.
wrote:

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heating is easier than cooling, you need max air flow for ac to work well and be efficient, so we use 8 inch when doing an a/c install.its pretty much the standard nowadays.lucas
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Old_Boat (Old snipped-for-privacy@thelake.com) said...

This is a case for an independent inquiry! If you wanted to know who made the best car, would you go to a Ford dealership to ask? It's a safe bet what their answer would be.
Same thing here, don't go to someone who is in business to sell you something to ask if you need it. Find an HVAC engineer and spend a few hundred bucks to have them do the analysis that tells you what you need. Then you take those specs to the conractors to get quotes for the job.
When we built our home, the heating plan (heat loss/gain calculations, plus the duct layout plan) cost $650. That gave me the specs needed for the heating subs we got quotes from, allowing me to compare apples with apples.
--
Calvin Henry-Cotnam
"I really think Canada should get over to Iraq as quickly as possible"
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Calvin Henry-Cotnam wrote:

That is very good advice! http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
- udarrell
--
WISDOM PRINCIPLED EMPOWERMENT COMMUNICATIONS -
THE REAL POLITICAL ISSUES and PEOPLE EMPOWERMENT
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