# Evaporative Cooler Duct Size



## Shooters

Hello all...

I'm in need of some help. I'm planning to install an evaporative side draft cooler (Mastercool) on the gable end of our home. I would like to duct the air a total of 33' with two drops. The 1st drop would be 8' from the unit into a 13' X 13' room and from there another 25' and end with a drop into living dining room area with a square footage of 900'. 

The 1st drop will need to be located approx 6' from the main duct.

At the moment I would like to use there 5000 cfm unit, but if it's a necessity I can purchase the 7000 cfm model. The outlet of the smaller unit is 18" X 18" and the lager is 20" x 20". 

What size duct should I start with? After the 1st drop do I need to downsize to increase velocity? What size should the duct be for the 1st drop? Finally, what suggestion for the size of the final drop?

I'm currently in the high desert of Ca, and this will concede with our are conditioning. 

I certainly appreciate all suggestion, after looking into this a bit, I'm somewhat lost.


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## beenthere

Trunk line should be no smaller then the units opening.

What size to the 13X13 room? How much cooling does it need?


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## flashheatingand

I don't recall seeing any swamp coolers being ducted a like the traditional setup. I believe, you could cut an opening for the first drop, and leave the end of the ducting open. But, I would check to make sure the cooler that you are installing is designed for __ static pressure.


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## Shooters

From what I understand so far, the 13 X 13 room would call for 500-675 cfm of air. I'm not sure if this is the correct answer to your question. If your asking about heat loss and heat gain, I don't know how to figure that out. 
I have contacted the manufacture and these units are commonly ducted, they did suggest that I do not use round duct. 
I have had two installers out, and both seemed to be just guessing. Both very different ideas. One advised to just tie into my current duct work or to run a downdraft mounted on the roof and just dump into the main room we would like to cool. 
The other wanted to use a 20" X 20" "trunk" and use an 8" branch to the 1st drop. Then downsize to 12" round to the end drop and use a 14" X 14" box? 
The problem I had with this idea was the severe downsizing, in consideration with the amount of air these units need to move to work. The 8" seems to me to be a bit small along with the 12". 
Another item I thought that would be important to consider is that this is a "wet" air for lack of a better term, and thus it would lose velocity faster than typical HVAC systems? Perhaps a 33' run is to long all together?

These Mastercool models seem to be more of the commercial unit if that helps? I would post an image but I need to make 15 posts... The model is ASA51 or ASA71

Again I really appreciate your thoughts and ideas.


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## thom

The 13 X 13 room needs two ducts to two boots and registers. The ducts should be 7". The 900 square foot room should have between 6 or 8 ducts, maybe even 10 depending on the configuration of the room. Again, the ducts are 7". 

Generally one combines the heat and cooling ducts however, it is likely that your ducting to the boots was not sized for evap cooling. Evap cooling takes more air-flow than heating so the ducts need to be sized for the cooling. 

You could size the main trunk line by the volume of the ducts to registers or you could just maintain the cooler outlet size. I'm surprised the manufacturer recommends against round trunk lines, they are common around here (New Mexico) even for evap cooling. Typically we would bring that 20X20 through the wall/roof then convert to 20" round. 

A 33' run is fine, and is not unusually long. 

Don't forget that the registers need to be at the far end from the windows that will allow the conditioned air out.


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## Shooters

Thank you all for your time and input! I'll let you know in the next few weeks how it comes together.


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## Dr Heat

Typically we would bring that 20X20 through the wall/roof then convert to 20" round. 

20" round is not 20X20 you would need 24" round its a bit larger but close is close


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