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Old 11-12-2018, 06:04 PM   #31
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Re: Installing Furnace in Attic


Heat from the ceiling doesn't make for a comfortable environment, and it's worse when there's no return air near the floor.

To get the air to mix properly, you have to have registers sized small relative to the airflow to increase the velocity and blow blown down with a lot of force, making it feel drafty.


Have no return air and it can be cold near the floor = cold feet, stat gets turned up just to be comfortable.

Just because something is done doesn't mean it's a good idea. A lot of stupid things are done, like installing vent-free gas fireplaces, sizing by 500 sq ft per ton and beer can cold refrigerant charging.

Things can work but not be optimal.
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Old 11-12-2018, 07:09 PM   #32
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Re: Installing Furnace in Attic


We install them in attics all the time. If thatís where you have to put it so be it. To keep the noise down donít butt your air handler or furnace directly against return. The unit will be much quieter with a three or four ft return duct. You donít have that option with a closet unit. Yes it would be more efficient if all the ducts were in your living area. A lot easier to do in new construction but not an existing structure. Things I donít like about attic installs in old homes is that without tearing out walls the refrigerant lines have to be run down the exterior of the house. As far as water leaks in ceilings there are things that you can do to prevent that. Install an oversized drain pan with a float switch. Also you can install a secondary drain to exterior as a backup in case of float switch failure. There are a lot of valid points in the above posts. Looks like you are doing your homework. Good luck with your project
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Old 11-13-2018, 06:57 AM   #33
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Re: Installing Furnace in Attic


Bayou,
My air handler is in the attic. I have a Carrier HE unit installed about 6 years ago and it works very well. My only complaint is the air handler is noisy. The return air is located is the center of the home in the ceiling hallway. I believe the air handler is butted against the return air box. I have a 3 ton unit and the return air opening is 24" X 14". According to research I have done, this is too small. I could add another 24" X 14" right beside it in the hallway. Would you recommend that or trying to find another location for a second return air duct? I do have a partially finished basement and I have one supply duct ran inside a wall to the basement. Should I try to add a second return air duct in the basement? (very difficult to find a path for it)
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Old 11-13-2018, 07:25 AM   #34
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Re: Installing Furnace in Attic


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Originally Posted by BayouRunner View Post
To keep the noise down donít butt your air handler or furnace directly against return. The unit will be much quieter with a three or four ft return duct.
Can you elaborate on this? What do you mean "don't butt the furnace against the return?" Shouldn't the return (and the supply) be firmly connected to the furnace for a sealed connection, not allowing conditioned air to leak out. And what do you mean about "three or four foot return duct?" I imagine the overall length of my return ducts may be upwards of 15+ feet, since at least one trunk will snake down the wall into the basement. Are you saying 3-4' (and no longer) is an optimum length? If so, I don't see how that's possible and still reaching every room.

Quote:
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A lot easier to do in new construction but not an existing structure. Things I donít like about attic installs in old homes is that without tearing out walls the refrigerant lines have to be run down the exterior of the house.
This project is part of a bigger 2nd story renovation, in which I'll have walls open and exposed. So I'm going to put as much in the walls as possible. However, I had not considered running the lineset in the walls. Until reading this, I was going to run them up the exterior wall of the house (assuming the furnace is in the attic). Is it okay instead to run them inside the walls? (yes, I know the suction line needs thorough insulation to keep moisture from condensing and creating a mold problem inside the walls).

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As far as water leaks in ceilings there are things that you can do to prevent that. Install an oversized drain pan with a float switch. Also you can install a secondary drain to exterior as a backup in case of float switch failure. There are a lot of valid points in the above posts. Looks like you are doing your homework. Good luck with your project
Great ideas for water protection. Yes, I'm doing tons of homework. Thanks to many contributors in this forum and Google, I'm learning a ton of stuff so I can maximize the outcome!
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Old 11-16-2018, 06:49 AM   #35
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Re: Installing Furnace in Attic


Bump.

Looks like @BayouRunner might have checked out of the convo. I was curious if anyone else might be able to share insight on his/her statements about not butting the return up against the furnace, and also the length of the return, as well as the lineset being inside the home walls.
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Old 11-16-2018, 10:27 AM   #36
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@m_ridzon , if you run the coolant lines in your walls, you may want to run them inside a 3” or 4” thin wall pvc with 45 angles for turns... IF they ever need attention you can snake them out and back in.. leave a strong braided robe in the chase to ease running wire/tubing etc up or down. Plug the chase with a ball of foam top & bottom
3” schedule 20 is available at lowe’s
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Old 11-16-2018, 12:02 PM   #37
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Re: Installing Furnace in Attic


Sorry never saw the reply. Itís a great idea to put the pipes inside the wall if you can. Pretty much all we do here in my area is attic installs. If you put a three or four foot piece of ductwork in between the filter return and the furnace/air handler itself it makes a big difference in the noise. A lot of contractors here butt it right up against the return just to get the job done so to speak. I like to feel the unit cooling, not hear it. You donít have to, itís just a suggestion


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Old 11-18-2018, 02:12 PM   #38
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Re: Installing Furnace in Attic


Quote:
Originally Posted by BayouRunner View Post
If you put a three or four foot piece of ductwork in between the filter return and the furnace/air handler itself it makes a big difference in the noise.
Are you saying the filter's proximity to the furnace in the return duct influences noise? I would not have suspected this. My return ducts will snake through the walls into a common trunk that returns to the furnace. Are you saying to place the filter somewhere upstream of the furnace 3-4 feet?
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Old 11-18-2018, 10:50 PM   #39
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Re: Installing Furnace in Attic


Quote:
Originally Posted by m_ridzon View Post
Are you saying the filter's proximity to the furnace in the return duct influences noise? I would not have suspected this. My return ducts will snake through the walls into a common trunk that returns to the furnace. Are you saying to place the filter somewhere upstream of the furnace 3-4 feet?
He's saying to make sure that you have at least a few feet of ductwork between the return air grill and the furnace. The more, the better. Your plan should be fine.

The filter can be at the furnace or at the grill, it doesn't matter. If it's at the grill, it's really important to seal the return air well. (it's important anyways as it'll be in the attic.)

Cheers!
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Old 11-18-2018, 11:11 PM   #40
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Re: Installing Furnace in Attic


Quote:
Originally Posted by yuri View Post
FYI subcooling and checking refrigerant charge is all done outside as you put your gauges on there. Subcooling requires measuring the temp of the liquid line as it leaves the condensor..
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Originally Posted by raylo32 View Post
Of course the gages go on the outside unit, my bad... d'ooohhh. I have done it a few times but it's been awhile. I guess that's a good thing.
Technically, we really only care about subcooling at the metering device, not at the condensing unit. It just happens to be convenient outside. All the manuals don't say much, because they know that no one what's to go into attics anymore then they need to.

With an attic install, measuring the liquid line temp at the AH would be a great idea if I didn't hate attic installs. (access is absolutely terrible in these parts.) You also need to consider the roughly 0.5 psi drop per vertical ft of rise.

We install service fittings at the AH when there's a significant difference in height, or distance from the outdoor unit.

PS. I've finally read through the thread. I stopped when I kept agreeing with everyone, including yuri. Attic installs suck, but in the end it's your house.

PSS. Ceiling registers also limit furniture placement. It really sucks to be directly under a cold stream of air.

Cheers!

Last edited by supers05; 11-18-2018 at 11:13 PM.
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Old 11-19-2018, 09:07 AM   #41
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Re: Installing Furnace in Attic


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Originally Posted by supers05 View Post
He's saying to make sure that you have at least a few feet of ductwork between the return air grill and the furnace. The more, the better. Your plan should be fine.

The filter can be at the furnace or at the grill, it doesn't matter. If it's at the grill, it's really important to seal the return air well. (it's important anyways as it'll be in the attic.)
Crystal clear. Makes perfect sense now. Although I do not envision a situation in my project where the furnace would mate directly against a room's return grill, I probably would have completely overlooked the potential noise issue. But now that it's been brought up here and I think about it, I suppose it would be a major noise issue, being that the furnace vibration would obnoxiously resonate through the walls.
Quote:
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You also need to consider the roughly 0.5 psi drop per vertical ft of rise.

We install service fittings at the AH when there's a significant difference in height, or distance from the outdoor unit.
Thanks for pointing that out. I assumed the vertical rise played a part in the line pressure, but nobody had brought it up here, thus I thought it was usually considered negligible.

Quote:
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PS. I've finally read through the thread. I stopped when I kept agreeing with everyone, including yuri. Attic installs suck, but in the end it's your house.
Thanks for stopping by to check out the thread. I've found that you usually have good, levelheaded feedback to share. I haven't yet made the decision to install in the attic, but I've been able to gather great feedback here to aid in the decision.

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PSS. Ceiling registers also limit furniture placement. It really sucks to be directly under a cold stream of air.
I suppose that would be a concern too. Honestly, I have no choice for my home since it currently has no 2nd story ducts. The most logical way to add ducts will be through the attic and with ceiling registers. To mitigate discomfort, I will probably try to use registers that have larger cross-sections, thus avoiding increased stream velocity as it enters the room(s).
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Old 11-19-2018, 09:54 AM   #42
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Re: Installing Furnace in Attic


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I assumed the vertical rise played a part in the line pressure, but nobody had brought it up here, thus I thought it was usually considered negligible...
The pressure decrease in a single story house is fairly negligible, especially for r410A. Obviously, more floors you add, the worse it gets. The temp is the bigger factor, as you can pick up quite a bit of heat running through a hot attic.

As for the registers, you need to maintain a decent velocity so that you get good mixing when in heating mode. (it'll mix be convection in cooling mode.) It does help mixing to have low wall, or floor returns. I usually suggest getting return air grills with dampers so that you can adjust between summer and winter. (high and low wall returns) Some designers will put high wall in the upper floors and low wall in the basement and main floor.

Cheers!

Last edited by supers05; 11-19-2018 at 10:00 AM.
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Old 11-19-2018, 10:05 AM   #43
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Re: Installing Furnace in Attic


Floor registers - furniture placement an issue - gimme a break. Unless it's furniture without legs that stops all air flow from a register.
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Old 11-19-2018, 10:07 AM   #44
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Re: Installing Furnace in Attic


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Originally Posted by SeniorSitizen View Post
Floor registers - furniture placement an issue - gimme a break. Unless it's furniture without legs that stops all air flow from a register.
It does stop mixing, which can cause stratification when cooling. (my old house had that problem because it used low wall registers instead of floor registers.)

Cheers!
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Old 11-19-2018, 11:04 AM   #45
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Re: Installing Furnace in Attic


Quote:
Originally Posted by supers05 View Post
The temp is the bigger factor, as you can pick up quite a bit of heat running through a hot attic.
Any suggestions on how to deal with such an issue?

Quote:
Originally Posted by supers05 View Post
I usually suggest getting return air grills with dampers so that you can adjust between summer and winter. (high and low wall returns)
Makes sense. This is probably a good idea regardless of having a basement or furnace attic.

Quote:
Originally Posted by supers05 View Post
Some designers will put high wall in the upper floors and low wall in the basement and main floor.
I don't fully understand. Please elaborate. High wall returns in the 2nd floor would seem best for summer cooling to the 2nd floor, but poor for winter heating to the 2nd floor. Low wall returns in the 1st floor would seem best for winter heating to the 1st floor, poor for summer cooling to the 1st floor. I don't understand how this makes sense since one floor is optimized in summer while the other floor is optimized in winter.
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