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.
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.
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, 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
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
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.
"I really think Canada should get over to Iraq as quickly as possible"
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.