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Return Air from Lean-To Back to Shop

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Forum topic by Steinbierz posted 11-15-2020 05:42 PM 298 views 0 times favorited 5 replies Add to Favorites Watch
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Steinbierz

146 posts in 1151 days


11-15-2020 05:42 PM

Hello,

I have an attached 10’ x 25’ lean-to on the side of my 1500 sq. ft. shop that I want to enclose so that I can put my air compressor and Felder RL-160 DC out there to free up some shop space. The space will be insulated and my only available entrance will be from the outside due to the common wall not being conducive to cutting a door into it. My main space has a commercial HVAC system.

I have read a lot of different threads about sucking your conditioned air out into your lean-to when the DC is running and the recommendation for having return air back to your shop. I have a lot of upper wall space (and some lower wall) on the common wall where I could have free communication between the main shop and the lean-to. Are there any “scientific formulas” required to figure out my opening sizes or can I just cut some decent sized holes and call it good? Also, is there any reason to build this out with some type of louvers between the spaces or just leave it open? Thanks.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)


5 replies so far

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Ruscal

73 posts in 192 days


#1 posted 11-15-2020 07:20 PM

Aren’t you creating a situation where you have to heat about 50% more area? Why not put the DC in a closet in the lean to with a vent back to the main shop? Then the rest of the lean to is unheated.

-- Have a hobby? You should have a business.

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ibewjon

2278 posts in 3807 days


#2 posted 11-15-2020 08:45 PM

I have a high velocity air conditioning system in my home. The air moves faster through smaller supply ducts than standard heating/cooling systems. So it is closer to a dc system. The supply splits into two 7” ducts. The return is two filters, 14×25 each. So maybe at least a 14×25, using a filter grill and a decent air filter to keep dust return to a minimum. Bigger sure won’t hurt.

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clagwell

364 posts in 807 days


#3 posted 11-15-2020 09:13 PM

To keep pressure loss down you should have at least twice the area on your return as the intake. There’s diminishing returns above four times the area.

Your DC has a 160mm inlet so you’re surely using six inch duct. That means a return size of 0.2 to 0.4 square feet.

As ibewjon says, bigger certainly won’t hurt.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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Steinbierz

146 posts in 1151 days


#4 posted 11-15-2020 11:28 PM



Aren t you creating a situation where you have to heat about 50% more area? Why not put the DC in a closet in the lean to with a vent back to the main shop? Then the rest of the lean to is unheated.

- Russell Hayes

Hi Russell. You make a very good point and one that I haven’t ruled out yet. BTW, the additional space will be 250 sq. ft…my building is 1500 so the increase in conditioned space will be ~17% increase in space. I realize I am conditioning cubic feet vice sq. ft. but the increase isn’t close to 50%.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)

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Steinbierz

146 posts in 1151 days


#5 posted 11-15-2020 11:32 PM



I have a high velocity air conditioning system in my home. The air moves faster through smaller supply ducts than standard heating/cooling systems. So it is closer to a dc system. The supply splits into two 7” ducts. The return is two filters, 14×25 each. So maybe at least a 14×25, using a filter grill and a decent air filter to keep dust return to a minimum. Bigger sure won t hurt.

- ibewjon

clagwell said…

To keep pressure loss down you should have at least twice the area on your return as the intake. There’s diminishing returns above four times the area.

Your DC has a 160mm inlet so you’re surely using six inch duct. That means a return size of 0.2 to 0.4 square feet.

As ibewjon says, bigger certainly won’t hurt.

Thanks guys…great info! I hadn’t thought about putting a filter between the two spaces but it makes sense thinking about it. I just have to remember to keep it accessible for maintenance if I go that route.

-- Larry ~ Alvin, TX (Home of Nolan Ryan)

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