locating air handler and returns

[airbare]

we are remodeling and have the option to put the air handler in a crawl space below the house or in the attic.

Obviously, this would imply air vents in the floor, if air handler is in the crawl space and vents near the ceiling if it is located in the attic.

Is it typical to place the return air opposite from the supply. For example, if the supply is on the ceiling is the return is near the floor? Or is the return always in the same place?

Is it common to install multiple returns to improve circulation and uniformity?

[genduct]

In general, the duct should be inside the building envelope which means inside the insulation
Just because you said the crawl or attic space doesn't mean this is impossible since the current thinking is to "basementize" your crawl or "cathedralize " your attic.
The crawl conversion is probably the easiest so why not consider adding the insulation and vapor barrier and use the crawl space

[motoguy128]

I would suggest usign the attic and making sure there is a nice large opening and pull-down stairs for access. Then as mentioned, consider insulating under the roof deck to make the attic a semi-conditoned space... and then suck out all that nasty fiberglass or loose fill cellulose crap. Ths isi how mine is set-up and it works well. It was a poor quality ductwokr install and leaks really bad. I estimate a 1/3 of my heat goes into the attic space... but now it at least mostly stays there and cna radiate partially into the house.


For the returns, it depends on your layout. A central return is easiest and cheapest, but you need to have the doors undercut or add "jump ducts" to allow the air a free path back to the central hallway space. Then you can just locate a supply(s) in each room just off center towards the outside walls. Duct runs should be sized based on heat load for each room. So for example, a large master suite migh get 2 or 3 8" supplies while a bathrom gets a 6" supply. Then include dampers on each branch near the supply plenum to balance it to near perfection. When set-up correctly, each room with heat up and cool down almost evenly... other than as affected by solar heat gain.

Multiple returns is generally better. But, in a attic or crawl space install it's less practical since you probably you may want filter grills rather than a centrally located furnace filter near the unit. With multiple returns, unless you only have 2 roms upstairs, you probably don't want to have ot change a 1/2 dozen filters. Then again, it's not a terrible idea to use a large media filter and use that as an excuse to have the unit serviced or visited at least once every 6 months. Not much harder ot go into the attic than it is using a short step ladder jsut ot change a filter on a grill at the ceiling.

[Shophound]

In general, the duct should be inside the building envelope which means inside the insulation
Just because you said the crawl or attic space doesn't mean this is impossible since the current thinking is to "basementize" your crawl or "cathedralize " your attic.
The crawl conversion is probably the easiest so why not consider adding the insulation and vapor barrier and use the crawl space

Plus one.

My :.02: for the OP...if you have no plans to insulate your roof deck, keep the furnace AND the ducts out of the attic. It will save you $$ and comfort compromises over the long haul.

Ensure all duct joints are sealed, regardless of where you eventually decide to locate them. That means duct mastic on all duct joints, seams, connections, and plenums. Also, ensure wherever a supply or return duct pokes through your ceilings, walls, or floors, that the gap between the duct box and the drywall is sealed. A little time spent doing this will reap comfort and energy saving dividends for years to come.

My vote in your case would be for equipment and ducts to be in the crawl space, with the strong encouragement for you to "basementize" the crawl space (that is, insulate the crawl space walls and put plastic on the ground). If you live in a humid climate, ventilating a crawl space is an exercise in futility.

[airbare]

I live near Los Angeles, so humidity is not a problem.

Our single story house previously had stratified air in winter, that often made it uncomfortable. The registers and return were both in the ceiling, so the cold air leaking into the house just sat on the floor. I know a tight envelope is supposed to fix that, but I've never experienced that, and I am quite paranoid about stratification now that we will be getting a 2 story home in a remodel.

Most contractors here recomment 2 separate systems, but that doesn't prevent stratification.

The idea is to have returns near the floor on the first story and near the ceiling on the second story. This should help to keep the air mixed year round, even if the ducts placement and velocity themselves don't provide very good mixing. As an added tweak, if each return is sized to be sufficient by itseld, I could, occasionally block one of the returns to take advantage of stratification when it suits (let the upstairs roast on hot summer days).

The crawlspace is tempting - it is the best way to minimize most duct runs. If we decide to put the HVAC in the crawlspace, I assume the registers go in the floor. Aren't floor registers more of a problem due to blockage?

[genduct]

I don't think that floor registers would change the surface temp of your floor enough to make you more comfortable.
What might help is insulating your crawl walls and perhaps the crawl floor and putting a little supply air into your now, non-vented crawl to really address the issue.
You do recognize that you should have posted your own post and not hijacked this one

[airbare]

actually, I started this thread.

Going back to the original topic, the HVAC guy stopped by this morning. He didn't like the crawl space (only 18" clearance, and lots of concrete walls blocking off rooms that would need to be cut), so the unit will go over the garage. And the supply air will come in from the ceiling.

I suggested putting the return near the floor so the hot air doesn't just hang out at the ceiling and leave a cold floor. Access shouldn't be an issue. The contractor said he didn't like that because it causes drafts that make people feel colder.

Where is the best place to locate returns in a 2 story house to minimize stratification?

[genduct]

My preference is high, so installing in the attic will work.

My suggestion about closing and insulating the crawl still stands and some small amount of supply air will help keep the space 'fresh' and also help with the comfort / floor temp- comfort issue as well

[Shophound]

I live near Los Angeles, so humidity is not a problem.

Our single story house previously had stratified air in winter, that often made it uncomfortable. The registers and return were both in the ceiling, so the cold air leaking into the house just sat on the floor. I know a tight envelope is supposed to fix that, but I've never experienced that, and I am quite paranoid about stratification now that we will be getting a 2 story home in a remodel.

Most contractors here recomment 2 separate systems, but that doesn't prevent stratification.

The idea is to have returns near the floor on the first story and near the ceiling on the second story. This should help to keep the air mixed year round, even if the ducts placement and velocity themselves don't provide very good mixing. As an added tweak, if each return is sized to be sufficient by itseld, I could, occasionally block one of the returns to take advantage of stratification when it suits (let the upstairs roast on hot summer days).

The crawlspace is tempting - it is the best way to minimize most duct runs. If we decide to put the HVAC in the crawlspace, I assume the registers go in the floor. Aren't floor registers more of a problem due to blockage?

Stratification within a dwelling, apart from the HVAC system, is caused by uneven heat gain or loss through the building shell, and air leakage. The thermal performance and comfort levels of a marginally insulated house can be significantly improved merely by tracking down and stopping the air leakage. The trick is to know where the leaks are, and how to stop them.

With your house being two stories, one system serving both floors offers a lot of challenges, whether you put the equipment in the crawl space or the attic. Floor registers are more difficult to work room furnishings around, and one must use caution to see they never become blocked by curtains, furniture, or other objects. Ducts for the level of the house furthest away from the air handler will need to be chased between floors, meaning either the second story gets floor registers, along with the first, if the equipment is located in the crawl space, or the second story gets ceiling registers, along with the first, if you choose to put the equipment in the attic. To properly chase ducts between floors, including returns, means not using wall cavities, and it means creating a proper chase to enclose and protect the ducts. Eats up a bit of floor space, which many people do not like.

There is no excuse for poor supply register velocity and volume if you are starting from scratch with new ducts. The registers should be located to where they can throw the design volume of air per room so that the air in each room is thoroughly mixed when the system is running. Floor registers should throw the air straight up (vs. deflected in a wide pattern as is common with floor register designs), and they work better if the air washes a wall and ceiling. Returns...have one per floor, and any room without a dedicated return and where the door will be closed a good part of the time, such as a bedroom, should have transfer ("jumper") ducts to allow the same amount of air to leave the room as is introduced to it by the HVAC. Again, do not use wall cavities as return chases. Repeat, do not do this. Use dedicated, sealed ducting only.