Mini-split p-trap

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Ortona

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I thought p-traps were always used on condensate lines from A/C air handlers (evaporators). But the installation instructions for my Daikin ductless mini-split does not show or call for a p-trap in the drain line. If I install one next to the air handler, will it cause me problems? Is it even needed? Perhaps there is p-trap setup somewhere inside the air handler. BTW, the unit is a heat pump system, if that matters. Thanks.
 

Jadnashua

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You'd have to pull the panel off and look...it may have one inside.
 
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Why would a mini-split need a p-trap?

It's a hose or tubing that just goes to the outside of your wall, and sometimes vaccumed by the exterior condensor unit.

P-traps are needed for indoor plumbing to protect from city main sewage gases.

A mini-split does NOT produce sewage gases.
 

Ortona

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Why would a mini-split need a p-trap?

It's a hose or tubing that just goes to the outside of your wall, and sometimes vaccumed by the exterior condensor unit.

P-traps are needed for indoor plumbing to protect from city main sewage gases.

A mini-split does NOT produce sewage gases.

I think a p-trap in a condensate drain line is put there to keep outside ambient air from being drawn into the air handler which when the blower is on operates at a pressure less than outside ambient pressure. Air drawn in the handler in that way might cause the improper draining of the condensate pan and consequently cause water leak out. So I understand the concept there---I am just wondering if the Daikin mini-split has a p-trap installed inside the air handler. I don't want to add a second trap unnecessarily and cause some problem with the drain system. As suggested I could take the cabinet apart an try to figure this out, but at this point I don't want to mess with the new unit in that way. Thanks for the replies.
 

Ortona

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You could try reading the instructions.

I did read the installation instructions and they didn't say squat about a p-trap--whether to install one or not to install one. I only ask this question because all the split A/C systems I've had in the past had p-traps installed in the condensate drain lines. So its got me wondering about this Daikin mini-split.
 

Dana

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On page 8 of the instructions for this Daikin mini-ducted series they also don't say squat about a p-trap. Instead they say:

Make sure that the piping is short enough with a downward slope of at least 1/100 and that there is no air bank formed. No drain trap is required.

On page 11 of this set of instructions for wall-coil type minisplits they state:

No trap is permitted.


Still no mention of a p-trap though. ;)

Drain traps on AC drains typically aren't necessary unless there are multiple air handler coils feeding into a common drain piping system, as is sometimes the case in larger commercial installations of mini-duct or ceiling cassettes.
 

Ortona

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On page 8 of the instructions for this Daikin mini-ducted series they also don't say squat about a p-trap. Instead they say:

Make sure that the piping is short enough with a downward slope of at least 1/100 and that there is no air bank formed. No drain trap is required.

On page 11 of this set of instructions for wall-coil type minisplits they state:

No trap is permitted.


Still no mention of a p-trap though. ;)

Drain traps on AC drains typically aren't necessary unless there are multiple air handler coils feeding into a common drain piping system, as is sometimes the case in larger commercial installations of mini-duct or ceiling cassettes.

Dana---Thanks for the links to the FXMQ and FTXN series of Daikin mini-splits. Of the two, the FTXN air handler appears to be very similar in construction to the FDXS series which I have. Unlike the instructions for my FDXS where no mention of p-traps or other wise is stated, the FXMQ is as you point out very clear that no trap is needed. So I am going to proceed to remove the trap which my technician installed on my drain line so that it conforms to the FXMQ instructions you provided. I appreciate your help.
 

Dana

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See page 8 of the FDXS manual, in particular the graphic of drain piping with the trap marked "WRONG", which has a trap like bend in it.

Keep the drain pipe short and sloping downwards at a gradient of at least 1/100 to prevent air pockets from forming.

Always sloping downwards would preclude a trap, no?
 
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I think a p-trap in a condensate drain line is put there
That's the problem, you saying "I think". Meaning, you don't know.
to keep outside ambient air from being drawn into the air handler which when the blower is on operates at a pressure less than outside ambient pressure.
Not going to happen.

It's so insignificant, the path of least resistance for vaccuum from the squirrel cage is going to be the air in the room, NOT from the drain.

Try to drink pop from a straw, but do this with your mouth WIDE OPEN as you hover the straw nearby. No amount of vaccuum from your mouth will suck liquid up from the straw.
 

Ortona

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See page 8 of the FDXS manual, in particular the graphic of drain piping with the trap marked "WRONG", which has a trap like bend in it.

Keep the drain pipe short and sloping downwards at a gradient of at least 1/100 to prevent air pockets from forming.

Always sloping downwards would preclude a trap, no?
Thanks for pointing out the diagram. It didn't look like the traps on the A/C condensate lines I've seen so I didn't think they were trying to draw a trap. But you are correct--in effect that's what it is.
 

hj

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acondensate trat is keep the conditioned air INSIDE the unit and prevent "sucking' outside odors into the system. The dimensions of the two legs have to be sufficient to compensate for the negative pressure in the unit. There is NO WAY an internal trap could be designed to do that, unless it was pojecting through the bottom of the unit.
 

Ortona

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acondensate trat is keep the conditioned air INSIDE the unit and prevent "sucking' outside odors into the system. The dimensions of the two legs have to be sufficient to compensate for the negative pressure in the unit. There is NO WAY an internal trap could be designed to do that, unless it was pojecting through the bottom of the unit.

Thanks for confirming what I thought was the case with traps on condensate lines. Now I can say I "know" what they are suppose to do instead of just "thinking" for which I was chastised earlier by a board member (HVAC'ker). Thanks again.
 

Matt38Fitter

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When it comes to these mini splits I have mainly worked on Mitsubishi. Yes the trap helps keep a cabin pressurized and not draw in air but this is in the case of a closed cabin. Every mini split I have done is an evaporator hung on a wall in the room with no duct work or "cabin". The drain runs inside the unit to an open to atmosphere pan and should not need a trap unless piped and tied into a open plumbing line.
 

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Dana

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This installation looks really weird- is it in some open car-port or something?

index.php


The proximity to the overhead duct work looks like it violates the vertical clearance specifications for the condenser unit (2" minimum for most Mitsubishis) , but for only a third to a half the width. How much that is affecting the net air flow and efficiency is an open question.
 

Mgloves

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IMC Section M307.2.4.1–Ductless Mini-split System Traps: “Ductless mini-split equipment that produces condensate shall be provided with an inline check valve located in the drain line, or a trap.” It’s an inexpensive and essential device for preventing insect, dirt, humidity and allergen infiltration. New codes coming into play with mini splits now.
I realize this is an old thread but it may help someone else.
 
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