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Old 07-06-2020, 08:58 PM   #1
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HVAC in attic FUBAR


A 1950s house with ductwork in the crawlspace, was abandoned in favor of its relocation in the attic with round ceiling distribution vents. A sibling (realtor) was convinced that putting a new horizontal Carrier air handler, AC and gas heating unit up in the attic was the best 'solution'. Unfortunately, this happened while I was preparing a conditioned crawl space unbeknown to me.

Might it better to relocate the horizontal HVAC unit, restoring it to its original location, although now horizontal and not vertical, with distribution ducts in the crawlspace? Now that I own the house, I'd like to ditch the natural gas and condition the crawlspace for equal performance as gas. Why would anybody locate an AC unit to the attic with only 2" insulation to protect against the superheated attic, vs condition crawl space?





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Old 07-06-2020, 09:22 PM   #2
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Re: HVAC in attic FUBAR


it's better to have the ducts in the crawl but changing over would be a huge job.

also, cooling distribution can be an issue when the house is 2-story and the supply ducts are under the house unless there's high level return on the second floor and the duct system is well designed/balanced.
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Old 07-07-2020, 06:38 AM   #3
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Re: HVAC in attic FUBAR


I read all these posts about HVAC units installed in attics... that is one thing that would put me off being an HVAC tech. I can't imagine having to service them in a dark, cramped 130 degree attic. I know some of you guys are great techs but how do you do really good work in that environment??
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Old 07-07-2020, 07:34 AM   #4
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Re: HVAC in attic FUBAR


In hot, humid paradise of FL, we have no basements so central air goes in the attic. When I think attic, I think of the spacious places up north that can be turned into extra living space.


In FL an "attic" may be 18 inches tall, if it is a complex roof with vaulted ceilings, it is like a jungle gym. A real workout to get to the equipment. I am too old for that anymore, part of my decision to use mini splits.


Wish I had a picture of my unit in the attic, horrible design. If I wanted to stick with central air, I would have built a platform on the end of the house and put it outside!
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Old 07-07-2020, 08:26 AM   #5
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Re: HVAC in attic FUBAR


I grew up in FL so have seen some of this in attics... and also crawl spaces. I have also seen other installs like my mom's house in FL where the heat pump air handler is in a closet on the main floor. That is also a horrible design, very little access to anything, but at least you can work within the insulated space. When they replaced her system a few years ago it actually required some dry wall, carpentry, and painting.

I know everything sells based on square feet of living space but I would gladly pay a little extra per sqft to make for or carve out a proper utility room. This is similar to the substandard garages in spec houses that always have that stupid room-behind-the-garage that makes the garages unusable just to up the living sqft a little.

One of my favorites is at the GF's sisters townhouse. The upstairs has 2 bedrooms on one side, a loft, and then a huge utility room on the other side that holds the water heater, air handler and propane furnace... with about 10 feet x 8 feet more of empty space, all within the insulated envelope. Could even put up a partition and turn that into a man cave and still have plenty of equipment access.



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In hot, humid paradise of FL, we have no basements so central air goes in the attic. When I think attic, I think of the spacious places up north that can be turned into extra living space.


In FL an "attic" may be 18 inches tall, if it is a complex roof with vaulted ceilings, it is like a jungle gym. A real workout to get to the equipment. I am too old for that anymore, part of my decision to use mini splits.


Wish I had a picture of my unit in the attic, horrible design. If I wanted to stick with central air, I would have built a platform on the end of the house and put it outside!
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Old 07-07-2020, 11:37 AM   #6
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Re: HVAC in attic FUBAR


I'm an amateur when it comes to HVAC systems, so I'll leave the location of the system to others to comment on.

I will only comment on the statement "I'd like to ditch the natural gas and condition the crawlspace for equal performance as gas."
If you're considering heating with electricity, rather than gas, you may want to look at the difference in utility costs. In my area, heating with electricity is 6 to 1 more expensive than gas, which I think is fairly typical in the US. If your heating demand is low, it may not matter much, but if you're heating a lot, the increase in your utility bill could be substantial.
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Old 09-23-2020, 02:17 PM   #7
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Re: HVAC in attic FUBAR


Atlantic coastal single floor home ~1100 sq ft with moderate heating needs and lots of solar potential with unobstructed south roof slope. A contractor suggested 16" round duct trunk with ~6 feeders to existing baseboard registers. Quoted $4900 which I thought was a bit steep. I would need to build out for the central return (12 x 16).

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Old 09-23-2020, 05:34 PM   #8
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Re: HVAC in attic FUBAR


For electric heat, a heatpump is the only way to go - forget electric resistance.

Having grid tied solar and trying to be "net zero energy" is not the same as actually heating the house with solar. The power comes from the same conventional power plants when heating and heating demand does not synch up with solar well at all.
Solar thermal is a better technology for heating because you can actually store the heat.

PV is not really good for heating imo. Produces too little electricity, out of synch and the efficiency of the panels is pretty low, well under 30%.

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A contractor suggested 16" round duct trunk with ~6 feeders to existing baseboard registers.
Did he do a room by heat loss/gain calculation? Doubt it.
That's essential when re-doing a duct system.
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Old 09-27-2020, 09:31 PM   #9
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Re: HVAC in attic FUBAR


I do have a room-by-room load analysis. However every planned improvement changes the calculations, as does increasing cooling from local effects of global warming.

For solar thermal heating, I was thinking of using the sand in the crawlspace as a thermal battery, heated by air collected by black screen behind glass or doubled wall polycarbonate, angled up against the block foundation. A small fan would push air under plastic sheeting to force it into the sand ground, with any excess heat diverted to living space. Landscaping can hide these low panels from street view, offset sufficiently.

So much heat, so many ways to harness and use it.

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Old 09-27-2020, 10:07 PM   #10
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Re: HVAC in attic FUBAR


You can get domestic solar hot water to cut back on electric use heating it.

Thermal battery stuff is less conventional and certainly less practical in a house that's already built.

For a new house, simplest form solar heating -> lots of south facing windows with overhang to block the summer sun. A high thermal mass floor - slab is best.
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Old 09-27-2020, 11:45 PM   #11
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Re: HVAC in attic FUBAR


I suppose crawl and attic installs are to save apprpx. 20 sq. ft. so more junk can be stored at 1st floor level. This down draft does a good job in a 3 ft. X 6 ft. closet centrally located with about 50 ft. of two 14" filtered returns in the attic.


There are 2 air pipes in the closet, 1 hi and 1 lo from the attic for combustion air and 1 flue pipe.



Pic --Blower removed for servicing. Pipe on the left in the closet is the basement gas furnace flue.




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Old 09-27-2020, 11:58 PM   #12
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Re: HVAC in attic FUBAR


Quote:
Originally Posted by jjrbus View Post
In hot, humid paradise of FL, we have no basements so central air goes in the attic.
That's nothing but a lack of knowledge. Houses have been built for over 60 years with supply ducts under the slab. When i was doing that as a grunt it was snap together ducts in-cased in grout. PVC pipe became popular later. That's how we cool our 1,800 sq. ft. with a 2.5 ton using about 40-50 KW / month.


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Old Yesterday, 09:28 AM   #13
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Re: HVAC in attic FUBAR


Quote:
Originally Posted by SeniorSitizen View Post
That's nothing but a lack of knowledge. Houses have been built for over 60 years with supply ducts under the slab. When i was doing that as a grunt it was snap together ducts in-cased in grout. PVC pipe became popular later. That's how we cool our 1,800 sq. ft. with a 2.5 ton using about 40-50 KW / month.


Edit: Edit:
For central air (cooling), having the unit in the attic is completely sensible; as sensible as it is for a heating system to have vents in the floor.
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Old Yesterday, 10:03 AM   #14
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Re: HVAC in attic FUBAR


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For central air (cooling), having the unit in the attic is completely sensible; as sensible as it is for a heating system to have vents in the floor.
Everyone has a right to an opinion so you do yours the way you like and i'll heat and cool my floor with ducts under the slab and benefit from any duct losses. The only thing i'd change if i were to do it again, the return ducts wouldn't be in the attic either but in the conditioned space. My water supply lines will be under the slab also, sleeved.
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Old Yesterday, 10:36 AM   #15
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Re: HVAC in attic FUBAR


Quote:
Originally Posted by SeniorSitizen View Post
Everyone has a right to an opinion so you do yours the way you like and i'll heat and cool my floor with ducts under the slab and benefit from any duct losses. The only thing i'd change if i were to do it again, the return ducts wouldn't be in the attic either but in the conditioned space. My water supply lines will be under the slab also, sleeved.
To each their own, I guess. If you're heating more than cooling, it certainly makes sense to have the vents in the floor. OTOH, for homes that require most or all cooling, having the A/C in the attic has some advantages. The air handler is not taking up space or making noise on the main floor of the house, the ducts are accessible and easy to modify if the layout changes, and you have less need for ceiling fans to circulate the air.

The house I lived in as a kid had the furnace in the attic and vents in the ceiling, and the temperature differential in the winter from floor to ceiling was as high as 30 degrees where we didn't have ceiling fans running. I would guess an A/C system with floor vents in a hot climate would suffer from a similar issue.
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