Rookie HVAC upgrade question
Greetings from Yucca Valley, California!
I’ve got an HVAC question for the room…mostly a matter of priorities. We are switching out an old-school condenser/handler for a heat pump air conditioner to lower our bills and dovetail with a solar install we’re doing in the fall.
So here’s my question, we’ve got R30 bats (or thereabouts) in the attic, but no insulation on the ceiling side. The ducts are in the attic. They are well insulated flexible ducts. So they’re decent but the attic is hot, hot, hot…into the high 120s on a regular basis in the summer.
The real issue is the garage where we’re installing the handler in the garage and that’s my concern. It’s out of the sun, which is a positive, but it can get very, very hot in the garage. So while we’re cooling the house to 78 degrees, the condenser is in full sun, the garage is over 100 degrees and the attic cocks in at 120. I’m curious where you think in all this bad news the system is most taxed.
I’ve been thinking that with our abundance of sun, I would consider getting one of the mini spits that has a built in Charge Controller and hook it up to panels. For the bulk of the day it would cool some area. But I’m wondering if it would be better to cool the handler and the garage, on an insulated attic and the well insulated ductwork up there.
Or am I totally off base? My last setup was in a crawl space so it was always cooler than the house.
what do you all think?
Mark
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Replies
The compressor can be outside in the sun - it does not have conditioned air in it.
You are correct to question why you would install an air handler and duct in a space that has the opposite temperature of what you are trying to condition the house to. Duct insulation is typically entirely insufficient to address this issue.
Common strategies for dealing with this include:
- Sealed crawl space that is the same temp as the house, with air handler and ducts in the crawl
- Semi conditioned attic, with the air handler and ducts in the attic
- locating the air handler and ducts such that you can build an enclosure around them and get them into the conditioned space.
You state you have R30 batts in the attic but also state you have no insulation on the ceiling. Where specifically is your insulation? Usually batts are installed in the attic, directly over the ceiling. Another method of insulating the attic is insulating directly under the roof deck, and bringing the attic volume into the conditioned space. Regardless of what specific strategy you employ
- You want to do everything humanely possible to air seal the conditioned space from the non-conditioned space.
- Whatever strategy you employ will have an impact on your HVAC load, so you are best served to do it in the proper order so you don't buy an oversized HVAC system. Oversized systems run far less efficiently
Suggest you do some googling on air sealing houses and conditioned attics.
Thanks for this...a great answer. My only mistake here was that when I was talking about the "ceiling" I meant the underside of the roof (the ceiling of the attic). The bats are all insulating the roof of the living space. So we're relatively efficient in here...but I'm just obsessing on the fact that all the cooling equipment is in two separate, uninsulated spaces.
So here's what I'd suggest...please check my work.
A better garage door to insure a better air seal.
A mini split to cool the garage.
Or would it make more sense just to seal the attic and upgrade the garage doors and window so that they're sealed and then run a duct into each form the new heat pump.
If we did that and ran numbers we could size a heat pump that ran the house and had enough left over to cool the attic and garage, which would now be within the conditioned space, although outside the sealed envelope of the house, where the thermostat could control the temperature.
Is that the call?
So is the attic insulated or uninsulated?
From your description it sounds like it's insulated, the insulation is under the roof. Of course, insulation is poorly done all the time, when I hear batts against the underside of the roof I automatically think it wasn't done right, but that's a digression. There is a concept in building science called the "building envelope," which is the boundary between the conditioned part of the house and the outside world. That's the insulation and also whatever keeps the weather out and an air barrier. In order to work at all the building envelope has to be continuous on all six sides of the building, if it's not heat can just go right around it.
What you'll often see is that someone tried to move the building envelope -- move the insulation layer from the floor of the attic to the ceiling. When they did that they made it so it's no longer continuous, there's a gap between the walls and the roof. And that ends up being like no insulation at all.
Also, until maybe 30 years ago the concept of the building envelope wasn't well understood and a lot of houses built in the 20th century have spaces that are kinda-sorta inside the building envelope and kinda-sorta outside. Your house sounds like it might be one of those.
For every part of the house you have to decide, in or out. You want all of your mechanical equipment inside.
DC!
we've talked before when I was building our off-grid cabin. What we have is bats laid on the floor of the attic, trying to keep the cool air in the house. As far as a continuous air barrier encasing the entire structure (best case scenario) that horse may be out of the barn on this one. The question is, with the air handler in a garage which heats up, and the insulated ductwork in the attic which would you put the most time and money into insulating and cooling?
And is there something wrong with directing new ducts to the attic and garage if we've made some effort to seal them off from the outside world? Is there some wasteful aspect I'm missing? Of course we're working harder to cool, but if the thermostat is in the house, wouldn't the interior temp be the tail that wagged the dog in this case...not bringing the attic and garage to 78 degrees in the summer, but cooling them appreciably.
where do you think my few dollars will give me the largest boost in the efficiency of a new heat pump ducted system? "And that's open to everyone!
It sounds like a classic "kinda-sorta" arrangement. You want the equipment inside your conditioned space because you want the conditioning the equipment provides to go into your space and not out into the outdoors.
Moving the boundary in the attic from the floor to the roof is a big deal and problematic if not done right. See this article for details: https://www.finehomebuilding.com/project-guides/insulation/five-cathedral-ceilings-that-work . If it's only ductwork in the attic, you're much better off just putting more insulation over the ducts. You also really want to make sure the ducts aren't leaking.
The garage is tougher, because generally garages aren't built to be insulated. I'd be thinking about building a mechanical room around the equipment and insulating that.
Makes perfect sense! Thanks!
And a smart fix regarding the attic. This is what I was after...looking for the few things that can be done to "improve" rather than hit a deep retrofit.
thanks again
Mark
Consider going ductless, the huge advantage is no equipment in unconditioned spaces bleeding energy.
Your old install maybe grandfathered in but putting the air handler in a garage is risky in that cars and the chemicals stored in the garage can be pulled into the equipment and the fumes spread throughout the home. Also, the ductwork is a huge hole in the fire wall that separates the garage from the living spaces.
Have a look at the concealed mini splits that might fit in a dropped hallway ceiling.
Moving the system into a fully conditioned crawlspace would be a great plan.
My guess is getting the equipment out of the attic would cut the power usage and equipment size 20% or so.
Walta