Upflow vs Downflow Air: Seeking Opinions

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rockncountry101
Posts: 79
Joined: Sun Mar 11, 2012 3:56 pm

Tue May 30, 2017 8:37 am

I am in the process of buying a new mobile home. I have decided on most of the features but one feature that I can't decide on is whether I want upflow or downflow air. If I choose upflow air my fear is that if something goes wrong with it I won't be able to access it to fix it. Upflow air uses the flex duct system so it should be quieter than the metal system underneath. Do you guys have any experience with upflow air? Thank you.


yakima4$
Posts: 80
Joined: Tue Oct 20, 2015 11:02 pm

Thu Jun 01, 2017 8:43 am

I would keep supply ducts under home.
A more temperate zone, less apt to be eaten by wasps and if something does go wrong they are accessible.

Mark440
Posts: 237
Joined: Tue Feb 26, 2008 8:33 am
Location: Anna, Tx

Thu Jun 15, 2017 5:16 am

Oh boy...you're gonna hate me for this!

Mine is a down flow. Had all new compressor (outdoor) and exchange unit installed. All went well until:

~ blower motor died within 5 years. Part was under warranty, but I had to pay labor. While the new motor was being installed, the tech commented he had never seen a down flow system that the motor didn't burn out about every 5 years. I don't know if what he said has any truth to it at all - but I'm right at the 5 year mark since he installed - and I'm "cautiously optimistic".

~ the ducting underneath is only as good as your skirting. Sounds silly - but if a critter can get in they love gnawing on flex duct. Add to it that some flex duct is hung with the plastic strapping - and that stuff is perfect for a critter to chew on - which results in all of it laying on the ground.

~flex duct itself isn't terribly expensive, and it's not difficult to work with * IF * you have sufficient clearance to go under to make a repair. Bear in mind that while the actual duct may be 10 or 12" - the whole thing is 13-16" in diameter due to the insulation wrap.

~supporting the flex duct is probably the biggest concern once you have each end connected and taped up. The stuff will swoop and swag - and can end up with performance impacting "squeezes" if the strapping isn't wide enough to support well. It HAS to be installed and hung "right" - or headaches will happen. Which can lead back to the initial headache of the blower motor burning out due to the excessive restriction....

If I was buying a new home - I would definitely consider having solid metal ducting installed. It can be hung with metal strapping - so the entire install becomes virtually impervious to a sneaky critter. Bear in mind also that flex duct is cheap - and the labor needed to install it is usually allocated to the low end of the pay scale. There's a reason for that.

Looking back - I cannot rule out a crease in the flex duct burning up the blower motor..... And yes, I will be eliminating flex duct.
Opportunity has a shelf life.

yakima4$
Posts: 80
Joined: Tue Oct 20, 2015 11:02 pm

Fri Jun 16, 2017 4:27 pm

If blower motors are burning out every five years there is a problem with the system not the motors. The installers are incompetent and not looking for the root cause of the problem.
You either lack a adequate return air path back to furnace or obstruction in duct flow. Motors usually last 10/15 years min.
You are correct, if you can afford to replace flex with metal under home it is the way to go.
Start with 90 degree fittings at connections to plenums or if triple wide a v box.
Insulate to R-8 and then wrap with an approved vapor barrier. Support @ 4ft O.C with P Tape or duct strapping.
I have done it. Not a fun job but increased air flow and peace of mind as far as rodents eating through it is great to have.

Mark440
Posts: 237
Joined: Tue Feb 26, 2008 8:33 am
Location: Anna, Tx

Tue Jun 20, 2017 1:12 pm

Something I forgot to include above.

Flex duct is - regardless of up or down flow - in and of itself less efficient than sheet metal ducting. The inner surface of the flex duct is distorted by the spiral wire wrap. I couldn't find a definitive source for calculating how much efficiency is lost in a perfectly straight run of flex as compared to a straight run of metal duct.

And, filters. Filters don't carry any rating information as to how much they restrict airflow. There are numbers stamped all over the packaging on particulate size - usually followed by different types of particulates (dust, smoke, etc) that are captured. But all of that comes at some level of cost to restriction of air flow. Further - getting a straight answer based on science is non-existent. The best advice I got was use a filter based on your needs - and not your fears. (If you don't smoke, why would you need a filter for smoke?) As it stands, I use the plain ol' fiberglass filters - and have the coils cleaned yearly.
Opportunity has a shelf life.

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