Air handler stand offs
I am all set to start running ducts for my ducted mini. I have a condensate drain pan on order (not sure i really need it but some extra insurance I guess).
I am placing the unit in a conditioned attic and originally planned on having it rest directly on the attic sub floor along with all ducts. However with the lip on the drain pan I will have to raise it about an 1″ or so.
My question is is there any concern with resting the unit and ducts on something like 2″ eps or xps foam board? I figured this will also have some sound dampening benefits as well.
This Fujitsu unit does have integrated brackets to hang from the rafters but I would prefer not to hang from the rafters as my air barrier is in place and I am not overly concerned about sound. I more concerned with clearing the lip in the drain pan so I’m not opposed to using 2x lumber if the foam is an issue.
Raul
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I would use vibration isolator pads for this purpose since they’re intended for applications like this, they’re designed to reduce transmission of vibration, and they’re available in various thicknesses. You can get them from grainger (https://www.grainger.com/mobile/category/vibration-isolator-pads/mounts-and-vibration-control/material-handling/ecatalog/N-9tx) among many other places.
I don’t think you’d have a problem with XPS, or type II EPS, but I don’t know how either of those materials would hold up over time in this application. I’d be especially concerned with how these materials may react if any refrigeration oil was ever spilled on them.
Bill
Type II EPS would probably work fine. In fact, I see foam pads preformed from similar weight foam all the time. EPS would also provide significant sound/vibration damping naturally. if you want more damping, a layer of soft rubber would help. Or make the pads out of polyethylene foam. Vibration damping is a bit of an art. If you want to do better than "OK", you have to design the damping for the vibration spectrum you expect to see. That gets complicated. But an EPS or polyethylene foam block along with a layer of rubber or soft/spongy foam would make a noticeable difference. And EPS should be plenty durable in a conditioned attic. Bill's concern above is valid, but since foam is so cheap, if it ever gets damaged you just replace it.
If you are making your own, they don't need to be big. You get better vibration damping when the foam is loaded. 3"x3" blocks at the corners would be fine. 2"x2" would even be strong enough.
Thank you both.
I just ordered some of the vibration isolation pads For the 4 outside corners of the air handler
I plan on using the specialized pads directly under the air handler and implementing eps under the ducts in an effort to save cost. I already have some half sheets of eps in 1/2, 3/4, and 1" so I will pick up a sheet of 2" and shim and level ducts as needed. The idea would be to cut in say 4" strips of eps and secure to the the floor with long cap nails or a screw and washer the same way I would secure full sheets to the exterior sheathing. After securing eps I will run some strapping over the duct and secure it as well to attic subfloor
On a separate issue pertaining to the ducts, I plan on running off the trunks with spiral 6" and 4" round in the ceiling joist bay just under the plywood subfloor.
As far as hanging these ducts I have seen galvanized strapping and fabric type roll intended for flex duct. Is one superior to the other? What of galvanized pipe strap like one you would find in the plumbing aisle. This is considerably cheaper and readily available. I assume the woven fabric type would be best for sound but what of the long term durabilty?
Raul
The fabric type is usually used for insulated duct since the fabric doesn’t cut into the insulation as badly. I’d use the galvanized strap if you’re using galvanized ducts. I don’t see any problem using the cheaper stuff in the plumbing isle. I buy the strapping in 100 foot bull coils and have used it for pipes, ducts, and the occasional other odd thing that needs a hanger.
I don’t see a need to anchor the EPS under the duct. Just set the duct on top of the EPS and use the strap over the duct to secure everything.
I like to use 1” long #10 hex head sheet metal screws of to secure the strapping. These screws are easy to install with a nutdriver so no issues with the driver slipping off or stripping out when you’re in a awkward spot.
Bill
You may want to use something other than foam, sometimes when things move against foam you can get a loud screeching noise.
Try rubbing 2 prices of foam together
Walt
The ducted units I've worked with are very quiet and vibration free. About the only you can just barely hear on them is the condensate pump. These are nothing like the old rattly belt driven central air units.
I wouldn't worry about any noise from either the unit or the ducting.
Akos Thanks,
encouraging to hear. I was never really overly concerned about the vibration more so just elevating the unit enough to clear the lip on the drain pan. This is the first unit in any of the homes I have lived in that will be located in the attic. All the others I have installed or maintained have be exclusively in unfinished basements. I was all set to start ducting then i realized I should probably slip a drain pan under it just in case. May never have an issue but better to air on the side of caution especially given the minimal cost of the pan.
Raul
Are you saying you have the option to locate your equipment and ductwork inside your conditioned space and made the active choice to locate the HVAC in the attic knowing it will need at least 15% larger equipment that will cost at least 25% more to operate so you can have more head room in the basement?
Walta
Walta,
This unit is specifically for the 2nd floor only. The basement and 1st floor are a separate unit.
The attic is conditioned. The main reason for this was so that I could locate the unit and ducts inside my envelope.
I wanted to keep the duct runs short and locating a unit for the 2nd floor 15ft down in the basement was out of the question.
I should also mention that my first floor was not demoed when I added my second story so my best most flexible option was the new attic.
I do not think there is much of a penalty with a conditioned attic but I could be mistaken.
My engineer that ran the numbers and designed my duct layout came up with 16k btus heating. I opted for the fujitu 18rflcd. A hair oversized but with the modulation on this unit I'm confident it will perform as expected.
Raul
Depending on the slope of your roof the insulated roof will have about twice the surface area of the ceiling. Now your house has 20% more surface area lousing heat so you need bigger equipment. Getting R 60 in between the rafters is difficult and expensive covering the ceiling with R 60 cellulose is cheap. Most end up with R30 between the rafters.
It sounds like you passed that fork in the road a while ago.
Walta