Drain pan for downflow air handler?

[kasander]

HVAC pros,

I am installing a Goodman HVAC system in my garage apartment and need help with the drainage requirements. The air handler has a primary and secondary drain on it. Am I required to also have a drain pan under the air handler? If so, how do I accomplish this with the unit in the downflow configuration? The air handler will be in a closet, and the duct will exit the bottom of the air handler and go straight down under the floor into the trusses. Am I required to put a drain pan with a square hole in the middle for the duct to go through? Or are the primary and secondary drain lines on the handler enough to satisfy code?

I am using the Goodman ARUF25B14 air handler and GSZ140181 heat pump.

The pictures show the approximate installation location. I am guessing I should build a stand to put the unit on top of so I can easily attach the duct to the bottom side of the air handler. Any help is appreciated.

 

[kasander]

Any experts out there that can give me some advice?

 

[LS6 Tommy]

Hang on a second, first thing, there is no such thing as a downflow unit designed to go straight down through the floor. The bottom of your unit needs to sit on a plenum. If you want to install it as a vertical (downflow) unit, you need set it on the supply plenum with the duct coming from the side and then down. The entire thing should be set up on blocks to facilitate the auxiliary pan. Most overhead units are installed horizontally and ducted down because it's the easier option in terms of hooking up the ductwork. An auxiliary drain pan is required when the air handler is located in a place that would cause water damage in the event of a leak. The drain for the A-pan must travel someplace where the water is readily seen when the pan is draining or a water level detection device must be installed.




Tommy

 

[86turbodsl]

Hang on a second, first thing, there is no such thing as a downflow unit designed to go straight down through the floor.



Tommy

Yes there is. Mobile home.

 

[LS6 Tommy]

Yes there is. Mobile home.

I kind of meant residential...

Tommy

 

[kasander]

This unit can be used in upflow, downflow, horizontal left, or horizontal right configuration. See attached from the installation manual.

My plan is to raise the unit up a couple feet on a stand, then attach a plenum to the bottom to transition from the square outlet to a 14" round. I will have a 14" round elbow that will direct the air from vertical to horizontal into the trusses.

I would prefer to keep the unit in the downflow configuration because I was planning to mount a return grill up above the unit, and all my registers will come up through the floor. I want to keep the twists and turns to a minimum so downflow seemed the most logical configuration.

If I have to switch back to a horizontal configuration, I will have to use more 90 degree and 180 degree bends to come out of the air handler and enter the floor system. My HVAC chaseway in the trusses is directly below where the air handler is shown in the picture.

Downflow Route: Horizontal through return grill on wall, through 1 foot of duct, through 1 90 degree to vertical and into air handler. Out of air handler and 1 90 degree bend into HVAC chase through trusses.

Horizontal route: Horizontal through return grill on wall, through 5 feet of duct, then 180 bend to come back through air handler. Come out of air handler and make 90 degree bend to vertical to go through floor, then another 90 degree bend to go back to horizontal through HVAC chase through trusses.

Upflow route: Not even going to bother with this.


Any ideas? Maybe it is best to call the inspector and have them tell me what I need to pass inspection. I am thinking I should be safe if I install a drain pan with a big hole in the middle and a wall around the hole.

Something like this:

Related questions, do I tee the primary drain from the air handler and the primary from the drain pan together, then route them out the wall and tee the secondary from the air handler to the secondary from the drain pan and run it out the wall as well? And do I need P-traps on all 4 drains before I tee them together?

Thanks guys for the input.

 

[LS6 Tommy]

I get what you're saying, but that drain pan idea won't really work. If you get a blocked drain or partially iced coil the water will go right down the duct. The A/H needs have a supply plenum, sit on a stand in the pan and have the duct come off the side of the supply plenum.

The primary and secondary ans auxiliary drains should never be piped together. It negates the purpose of the secondary and auxiliary drains. Trap the primary drain on the unit. Run your primary unit drain to where ever you want it to drain. Run the secondary down to the auxiliary pan. Run the auxiliary pan drain out of the building where you can easily see of water is coming out of it. When it's feasible, I like to bring it out over a window. If you can't do that, install an auxiliary pan float switch that cuts off the cooling.


Tommy

 

[kasander]

Well, that messes up my plan. Why do they include instructions for downflow installation if it's not intended to be used that way? I even had to buy the downflow kit to change the configuration. (It was some overpriced sticky-backed foam that I had to stick on to prevent condensation).

I don't really understand why you say a blocked drain would allow water to go into the duct. That is the whole purpose of the secondary drain...

So on the drain situation, I need a total of 3 drains? Primary, Secondary from the air handler, and an auxiliary drain from the pan.
Let me make sure I understand:
-Primary from A/H goes through a trap and outside.
-Secondary from A/H goes through a trap and into the drain pan.
-Auxiliary from drain pan goes outside (No p trap needed here).


How would you typically install an A/H where the supply duct work is under the floor and the return is up high on the wall? I am guessing the horizontal configuration? I just really wanted to avoid all the extra turns in the ductwork to accomplish this.

Someone mentioned mobile homes using downflow configuration. Are they required to have a drain pan?

Doing more reading. This page says: The International Residential Code (IRC) addresses this problem with a requirement that “a secondary drain or auxiliary drain pan shall be required for each cooling or evaporator coil where damage to any building components will occur as a result of overflow from the equipment drain or stoppage in the condensate drain piping.”

The key word there being "or." So, I read this as since the A/H has a primary and secondary drain, I don't need a drain pan...

 

[LS6 Tommy]

I always try to admit when I'm wrong, and I just looked at the install instructions for a similar unit from Lennox. They show it as being done the way you want to, but they do not mention an auxiliary drain pan.

That being said, a pan is required by code with or without a secondary drain on the unit, so I'm not really sure now what to tell you other than what I have seen in the past with a plenum on the bottom.

When the drain is blocked, the condensate pan inside the unit overflows and the water will just run down the inside of the unit. Once the unit gets saturated and fills up, it will run down the supply flange into the duct. That's why they don't make auxiliary pans like the one you drew.

You don't have to trap the secondary drain on the unit.




Tommy

 

[kasander]

Tommy, thanks for your insight and help. I appreciate you looking into it further.

When the drain is blocked, the condensate pan inside the unit overflows and the water will just run down the inside of the unit. Once the unit gets saturated and fills up, it will run down the supply flange into the duct. That's why they don't make auxiliary pans like the one you drew.

I am still a little confused by this statement. If the primary drain is blocked, the pan will not overflow. It will simply drain through the secondary drain.

I think the best thing to do is talk to my local inspector and see what he wants to see.

 

[kasander]

Also, I think I should P-trap the secondary drain as well to prevent air from being drawn through it. It doesn't function any differently than the primary drain, it is just at a higher level...

 

[LS6 Tommy]

Tommy, thanks for your insight and help. I appreciate you looking into it further.



I am still a little confused by this statement. If the primary drain is blocked, the pan will not overflow. It will simply drain through the secondary drain.

I think the best thing to do is talk to my local inspector and see what he wants to see.

You're correct about the primary/secondary drain function. As long as they are piped separately, there shouldn't be any true risk of an overflow. The problem arises when they are improperly tee'd together and the drain line itself plugs.

Talking to the inspector is not a bad idea. Just remember, an inspector can't dictate what you do based on his personal feelings, he can only tell you if what you are doing meets code or not. I've dealt with inspectors that have told me "I want you to do XXXX." I politely ask them to show me where code requires what they're asking me to do. There have been more than a few times what they told me I "have" to do was not required by code.

Tommy

 

[brewchief]

Your inspector may allow a float switch installed in the secondary drain port to shut the unit down instead of a drain pan.

A trap on a secondary drain doesn't make sense since there should never be any water in it to create a seal.

 

[Highbeam]

I'm no HVAC guy but in the PNW we build a lot of homes on top of crawlspaces. Run the heating ducts in the crawl to floor registers and the return duct up into the attic to a ceiling intake. Just about all of the air handlers are downflow with conditioned air dumping straight out the bottom of the unit and the return air duct plumbed into the top of the unit. It's not weird to want to set up the goodman this way.