Need Another Return, But Where?
Getting close to a decision on equipment and installer to replace my dead 3.5 ton Rheem HP. Leaning heavily toward the 3 ton Greenspeed. Will include some minor reducting to correct the overcooling in the guest bedrooms in the front half of the house closest to the air handler. These ducts currently run directly from the top of the supply plenum to each of two b/r's, the guest bath, and the laundry room (where the air handler sits). Contractor will disconnect these ducts and add a trunk duct to the plenum to a new distribution box where the ducts will be attached (with hand dampers in case further adjustment is needed).
Also need more return. Existing return filter grille is 20x20 in the hallway near the guest b/r's. It's near the floor and feeds through the wall to the cavity under the air handler stand inside the conditioned laundry room. Initial plan was to add another 20x20 filter grille near the floor feeding through the wall to the same cavity, but around the corner, which puts it in the entry foyer. I now see there may be a better place to put this second return filter grille, but I need some thoughts from you pro's, please.
Realize my entry foyer and "front" door is actually on the side of my house. The entry foyer opens directly into the atrium area (which is surrounded by sliding glass doors). From the foyer, turn right into the hallway leading to the front of the house with the guest b/r's and guest bath. The tstat and return are in this "guest wing" hallway. From the foyer, turn left to enter the hallway leading to the back of the house, where the main living area is, along with the master b/r and bath.
Would it be better to put a jumper duct from the cavity under the a/h (run it beside the a/h up through the ceiling), through the attic to a new filter grille in the ceiling in the hallway that leads to the back of the house where the main living area is, along with the master b/r?????? My thinking is that the air supplied to the main living area currently has to move a long, long way to get back to the one return in the hallway at the front of the house. Adding a return around the corner from the existing return wouldn't shorten that distance any.
Do you need a drawing or a picture?
Personally id have air returning inside your house than through a hot attic space.
Pictures and/or drawings always help. A proven, sure fire way to increase thread participation on hvac-talk, that's for certain.
Your existing 20 x 20 return...does it open directly to the cavity beneath the furnace, or must it go up the wall cavity before entering the furnace?
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
So a return in the foyer is better, even though the foyer has doors to the outside and it's far from the other rooms? The rooms are all open (no doors between) and the mbr door stays open. One contractor suggested the jumper through the attic for the added return. All others never suggested a return duct in the attic, so that's why I ask for advice here.
Originally Posted by SBKold
Opens to the cavity under the a/h. I have a hp only, no furnace (Florida). All supplies are in the attic... nothing in the wall cavities.
Originally Posted by Shophound
Posting from my Droid, PC problems right now. Will try to post pix soon.
Originally Posted by Shophound
It's best to keep as much duct out of the attic as possible, also the return nearest the ah will tend to pull most of the air bc air is lazy and will always choose the shortest run. With that said, it would be better to more evenly distribute the return air by having a return on the other side of the house and would help to balance out the hot/cold spots in your home. As long as the contractor uses a high r-value insulation on the new duct and completely seals all the joints it would probably be better for your comfort while not as good for efficiency. Have you looked in to spray foaming your roof deck? Doing that would greatly increase the efficiency of your duct work since it would then be in a semi-conditioned space rather than a sweltering hot attic.
So either way is OK? Comfort in the main living areas/mbr at the back of the house hasn't been a problem with the one 20x20 return. I thought adding a ceiling return near the back would be more efficient. If that's not the case, maybe I should just go with the "easy" way to add a return... through the wall in the foyer to the a/h cavity... provided proximity to outdoors isn't a problem.
Originally Posted by jtrammel
As to foaming the roof deck... I may consider it in the future, after the existing roof is replaced in a few more years. I'd hate to spend money foaming and then find some of my roof sheathing needs to be replaced during the re-roof.
drawing of house layout & pics will help. please take one showing equipment/platform & return below.
"Initial plan was to add another 20x20 filter grille near the floor feeding through the wall to the same cavity, but around the corner, which puts it in the entry foyer. "
not a bad idea, easy enough to do..but.. in the atruim.. in florida..that kind of gives me pause.
according to what you wrote...and please correct me if I'm wrong..the current r/a
is on the opposite end of the house from master bedroom & general living area?
things like jump ducts and/or transfer grills will help to return air from master..
how many supplies in the master area?
your ahu closet would have to be pretty big to allow a return duct to be put from
return on bottom, to besides the equipment..and back into attic to terminate at
new location. do you have that kind of room?
will top of this closet be sealed air tight to attic when new trunk/supply plenum is installed?
depending upon the size of r/a needed..sometimes closets are located centrally and you
can give up a portion of the closet for r/a. or even a corner of a room..but this would involve
a good bit of carpentry work.
post the drawings & pics..we'll take a look.
it would be nice to keep r/a in conditioned space, but in the big scheme of things..
putting the supply ducts in conditioned space is the better way. doesn't always
fit into the overall project scope.
but jtramel is right..putting ducts in semi conditioned attic (foam sealed attic)
would be a good savings & improve performance of equipment.
nice to see someone involved in getting it right.
best of luck.
The cure of the part should not be attempted without the cure of the whole. ~Plato
One more thing to consider.
May not be able to put a 20x20 filter grille through the wall to the a/h stand cavity from the foyer. The interior width of the cavity on that side is approximately 25 inches. Within that space there are 2 wall studs on 16 inch centers. I'm thinking a filter grille 14" wide by 20" high is about all that will fit without cutting out both wall studs. I'd hate to leave the upper wall in that space supported only by the door frame and the corner support. Refer to pictures to be posted soon.
20x20 plus 14x20 gives me 680 square inches. I believe that would be plenty for a 3-ton, considering the existing 400 square inches has been in use for over 30 years with a 3.5 ton.
Can't post all 15 pix at once. Here are the first 9 with 6 more to follow. File names are descriptive.
I don't see enough room to get a return duct up beside the air handler. Regarding a return duct in attic the air would pick up some heat as it traveled through the attic therefore adding to the heat gain of the duct which would slightly increase the temperature of the evaporator coil resulting in less efficiency. Supply ducts in the attic do the same which slightly if well insulated or drastically if not well insulated increase the supply air temperature. It also takes the unit longer to cool down the duct when the unit comes on resulting in decreased efficiency.