Author Topic: Attic Insulation over HVAC unit  (Read 735 times)

dneck37

  • 5 O'Clock Shadow
  • *
  • Posts: 17
Attic Insulation over HVAC unit
« on: March 08, 2020, 04:00:30 PM »
Hey Everybody, I have a 100 old house with sub par insulation. Its roughly R20 and recommended for my climate is R49 (I live in the upper Midwest). I also have flexible AC ducts that are above the R20 insulation. I believe these ducts are only R4, but exposed to the rest of my hot attic in the summer. I want to add insulation everywhere, but I have a HVAC unit(some call it an air handler in this space).

My plan would be to add R30 unfaced Fiberglass batts all over the attic, but I am not sure what to do with the air handler. Can I lay batts over the top of the air handler? If I dont, this will be the least insulated part and stay at R20, kind of making my other efforts meaningless. The handler occupys roughly a 3ft by 10ft space on top of a larger playwood base. If I lay the batts over it then I create an air pocket since they wont completely fit up to the unit, but they can be easily moved to service the unit. I think this also allows for the condensation float switch tray under the unit to still work properly, since the batts wont be sitting on the tray absorbing water. There will be an air gap between the batts for any moisture to escape from the unit. These air gaps aren't great but I thought this would still be better than my current situation.


Anyone have any thoughts or better ideas? I was trying to avoid attempting to disconnecting/disassembling the handler and raising it by putting something like 2 by 10s under it to fit the higher r value insulation batts.

Fishindude

  • Handlebar Stache
  • *****
  • Posts: 2344
Re: Attic Insulation over HVAC unit
« Reply #1 on: March 09, 2020, 08:44:34 AM »
Not a good idea to bury your air handler in insulation.
I would want insulation back away from it at least a foot or two all the way around.

Always hated equipment in an attic or crawl space because it's a bear to service and therefore hardly ever gets serviced.
If you ever upgrade and there is any way possible, relocate the air handler to someplace more accessible at that time.

dneck37

  • 5 O'Clock Shadow
  • *
  • Posts: 17
Re: Attic Insulation over HVAC unit
« Reply #2 on: March 10, 2020, 07:46:57 AM »
So even if i used batts that could easily be pulled away, you think its still a bad idea? Is it a moisture issue? I was thinking and maybe a better option would be building a box around it with removable tops and sides. That way I can insulate all around it but still have "breathing" area for the air handler

zolotiyeruki

  • Magnum Stache
  • ******
  • Posts: 3501
  • Location: State: Denial
Re: Attic Insulation over HVAC unit
« Reply #3 on: March 10, 2020, 08:06:59 AM »
If it were me, I'd get some 2" styrofoam sheets ($25-30 for a 4'x8'x2" sheet) and build a box around the air handler.  And then add batts or blown-in insulation around that.  Make sure, though, that if that air handler includes a furnace (almost certainly yes), that it has a clear inlet and exhaust for combustion.

I'd also replace all the flex ducts with rigid ducts (for better airflow and sealing) and then bury them in blown-in insulation.

BudgetSlasher

  • Pencil Stache
  • ****
  • Posts: 812
Re: Attic Insulation over HVAC unit
« Reply #4 on: March 10, 2020, 05:21:12 PM »
How old are the ducts?

I hate flex duct, it kinks and collapses too easily, it is often poorly installed or supported, rodents seem to love it, the air flow is horrible, and when it gets old is gets brittle (and if it breaks you have air leakage out and fiberglass getting in to the air stream). I would replace the flex duct with rigid duct work; some people do like to have the last couple feet as flex to isolate any vibration (it is a decent compromise, I suppose).

I also hate the way people see "insulated flex duct and think that it is ok to put it outside of the conditioned space; insulated flex duct is only R-4 (if I remember correctly).

Ideally you want the HVAC unit and all of the duct work to be inside of the "conditioned space"; in other words; the insulation should be beyond the HVAC parts).

zolotiyeruki's, to me, seems to be a good economy route. If I went this route,I'd probably build a real utility room around air handler, remove the insulation below it and insulated the "room" from the attic. I completely agree with replacing the ductwork with rigid metal ducting; I would also seal it with mastic. They I also would bury it in insulation.

In an ideal world and with and ideal world I would move the insulation to the underside of the roof. There are ways to maintain a connection between the eave and ridge vents while adding insulation, or perhaps you are a good candidate for a hot roof. This would allow you to increase the R-value, improve air sealing, and bring the HVAC inside the conditioned space all at once.

One thing I would do is air sealing, in a 100 year old house air is likely leaking into attic (and out of the house) from everywhere. And air loss can be a big cause of heat loss, likely more so in an older house. Unfortunately to do this right you really need to pull up all the existing insulation to ID the air leaks.


dneck37

  • 5 O'Clock Shadow
  • *
  • Posts: 17
Re: Attic Insulation over HVAC unit
« Reply #5 on: March 12, 2020, 09:37:10 AM »
The ducts look pretty good, all seem to be intact with no crushed sections or cuts. I have already air sealed all the gaps in my attic with spray foam so I'm good there. I think I need to seal the connection between the ducts and the air handler better though. 

I think i will be going with the utility room/box around the air handler. It does not have a furnace integrated to it. I have hot water radiators for heat (1920s house).

I explored the insulation under the roof idea and it seems to be extremely costly, at least with my local contractors. After rebates It would cost me around $6000. That's a long payback period vs the box and added insulation. Also I cant really turn my attic into a finished space, I have too many support structures jutting around.

ChpBstrd

  • Handlebar Stache
  • *****
  • Posts: 2025
Re: Attic Insulation over HVAC unit
« Reply #6 on: March 14, 2020, 09:47:18 PM »
I would:

1) Probably not build a box over your HVAC unit. Seem like a lot of things could go wrong there, for minimal benefit. I might consider gluing rigid foam on some of the sheet metal panels, or just laying a piece of unfazed batt over the top of a horizontal unit. Beyond that and you're experimenting with outcome factors like fire, carbon monoxide, and condensation.   
2) See if I could slide a couple inches of rigid foam under the drip tray where you can't blow in insulation or add batts. Good news, the flex duct won't stop you!
3) Ductwork is hard and expensive to insulate to any reasonable amount. Here's an easier way for long stretches. (1) Screw stakes to the ceiling joists along both sides of the ducts, so they stick up in the air. (2) Staple landscaping fabric (which is cheap) to the stakes, creating a little fence that goes alongside your ducts. (3) Blow cellulose into the cavity created by the two fences alongside your duct, burying the duct under a foot or so of cellulose on all sides. Note that this uses a LOT of cellulose, but cellulose is cheap. For the short stretches, or where the duct goes through the ceiling, Just drape a big batt over them and dust over them with cellulose.
4) If high attic temps in the summer are a concern, radiant barriers on the rafters are cheap and easy. Also, 100 year old houses rarely had enough ventilation, so add a whirly vent, a ridge vent, and/or some intakes in the porch ceiling. When you replace the roof someday, go with a light color.
5) The #1 efficiency killers for forced air systems are grossly undersized intakes. If you have this problem, fixing it will save more energy than a lot of the insulating ideas. 
6) The #2 efficiency killer is dirty inside and outside coils that have never been cleaned.