# Mini split drain line question?



## charliefreak100 (Jun 20, 2014)

Hi

I'm self-installing a concealed, ducted mini split. This unit:

http://www.mitsubishipro.com/media/255148/sez-kd15na-suz-ka15na_submittal.pdf

(Not doing any of the actual hook-up... just siting the unit and running ducts, drain and rough-in of wiring.)

My question is about what to run for the drain line. The drain attachment on the air handler (head) states that it has a 1-1/4" diameter, which means I need to use a drain line with a 1-1/4 internal diameter. This seems huge to me! Even my main two-ton whole-house air-handler only has a 5/8 i.d. drain line.

Does anyone know why such a large diameter drain line is needed? And whether it would be possible (or cause any problems) to adapt it to a smaller diameter. I am planning to run the drain line down through three floors and my job would be much easier with a smaller gauge drain.

Many thanks

Charliefreak


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## Doc Holliday (Mar 12, 2011)

firstly, why running ducts on a ductless mini split? how? where to? mini split?

Secondly, post pics of these instruction in which a 1 and 1/4" drain is required for any mini split and as well a pic of the actual drain exuding from the mini split.


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## beenthere (Oct 11, 2008)

charliefreak100 said:


> Hi
> 
> I'm self-installing a concealed, ducted mini split. This unit:
> 
> ...


Its because the condensate pumps they use are not very strong. So they use larger drain lines to decrease resistance so the pumps can work. 

If you have the room to run off of the bottom drain, you don't need as large of a drain line.



Doc Holliday said:


> firstly, why running ducts on a ductless mini split? how? where to? mini split?
> 
> Secondly, post pics of these instruction in which a 1 and 1/4" drain is required for any mini split and as well a pic of the actual drain exuding from the mini split.


Page 3 of the PDF he linked to has a pic of it.

Its a ducted mini split, not a ductless. Ducted mini splits have been around for a long long time.


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## charliefreak100 (Jun 20, 2014)

Many thanks Beenthere. It's tricky to find people with experience of these units.

Unfortunately I do need to make use of the built in pump as I need to run the drain line across the ceiling before it goes down through a wall to the basement. I wonder if I could use the 1-1/4 line for the lifted section, then transition to a narrower tube when I run down through the wall?

Second question: If I install an drain pan sensor in the unit e.g.

http://ecomfort.com/diamondback-drain-pan-level-sensor-27383.html

should I also add a secondary drain pan underneath the unit, or can I get away without this?

Thanks

Charliefreak


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## yuri (Nov 29, 2008)

They probably tested it and the pump has enough capacity to quickly fill a smaller line and then it will create head pressure/back pressure and overload it. A 1.25" line will probably never fill up and will always have some air space above the water so it can siphon and drain quickly. That may be an issue with a smaller line. I have had LOTS of problems with horizontal units like that and mini splits not draining properly as they get air locked. I would try use a full size line or pump it straight out thru a wall and not go down to the basement if possible.

A secondary drain pan is ALWAYS a good idea with an overflow sensor/alarm.

Pumps fail, drains block from algae buildup etc etc.


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## beenthere (Oct 11, 2008)

It has a drain sensor. But if you can fit a second float switch, or a secondary drain pan, that would be a god idea.


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## cenfl (May 8, 2016)

Howdy,

Apologize for scabbing to an old thread, though was reading post in regard to using the same ducted mini split that I am sticking in an addition in our home here in Florida... I can't seem to figure out from the instructions if I need to use the drain line on top with pump or if the bottom holes are gravity lines I can use etc? The instructions sure don't clarify things... Any help if greatly appreciated.


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## yuri (Nov 29, 2008)

Looks to me if it comes with a pump you use the hole with the pump. The top hole is for emergency use in case the pump fails and you need to connect it to a drain. If it does not come with a pump then you use the lower drain and should hookup the top drain too. If the lower one plugs with algae and it overflow out the top one it needs to drain somewhere.

Those pumps are notorious for failing and the problem is building a strong small pump for a reasonable price. They are tiny and that is hard to do.


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## cenfl (May 8, 2016)

Thanks for response Yuri.... actually looking for specifics here as the manual does not clarify whether to glue the bottom holes closed etc? Cheers,


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## charliefreak100 (Jun 20, 2014)

You can do either. 
* You can use the bottom outlets and a gravity drain (this is the best method)
* Or you can use the bottom outlets and install your own external pump
* Or you can block up the bottom outlets and use the built in pump (top outlet)

If you go for the first two, the built-in pump will never kick in, because the water level in the drain pan will never be high enough to trigger it.

In the end I connected the top outlet (the outlet for the built-in pump) and used the enclosed bungs to stop up the bottom outlets (I added screw clamps to make sure the seal was tight, but I didn't glue them shut).

This works, and the built-in pump does pump the condensate away.

However, I don't think it 'empties' the drain pan as well as a gravity drain (or external pump off the gravity drain) would. I've noticed that the unit isn't as good at lowering humidity as I would have hoped (it's correctly sized) and I suspect it's because water is sitting in the drain pan and evaporating back into the air.

I am planning to install an external pump and only use the built-in as a back up. 

If you have the facility to run a simple gravity drain off one of the lower outlets I would absolutely recommend that.


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## yuri (Nov 29, 2008)

Yeah a large gravity drain is always the best. Minisplits unless used year round will have stagnant water in the drain in the off season and in my experience it creates algae and blockages eventually. If you flush the hose with bleach yearly it is not a issue and checking the drain is normal maintenance with regular resi units anyway.


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## supers05 (May 23, 2015)

The last Mitsubishi seminar I attended, mentioned that it's a good idea to plug the top drain if it's not used. (or at least unplug the wire) It apparently will spit some water every now and then. Not a flood type situation but just aggravation.

Those internal Pumps have a very limited lift ability. The manual will specify the size and length of the lift. This is because there's no check valve and is calculated based on the volume of the pan. (The condensate runs back into the pan and will overflow it the lift is too long) 

Cheers!


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## charliefreak100 (Jun 20, 2014)

Thanks Supers05. Do you think it would be a good idea for me to switch over from the built in pump to an external pump (keeping the built in as a backup)?

Is my diagnosis of my humidity problem correct? (I.e. Water left in pan evaporating back into air)

When I tested the internal pump it worked fine, but left about a pint of water undrained. The gravity drain empties the pan completely.


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## supers05 (May 23, 2015)

As long as you empty both pumps onto a gravity drain, it'll work. You can't connect the 2 discharges though where there'd be pressure. 

I do believe the extra water in your pan is adding to the situation. They do have a dehumidify mode though. This is where the fan and compressor slows down to the minimum, keeping the coil just above freezing. (dehumidifies the best this way) Leave the fan speed option on auto. High speed fan will decrease dehumidification. 

Cheers!


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## charliefreak100 (Jun 20, 2014)

Supers05... you clearly understand these units! Thank you. I've struggled to find someone who knows what they're talking about with these specific types of minisplit.

Would you have a second to look at the diagram below, which shows my current setup, and how I am proposing to alter it:










Do I need to add a vent of any kind? (I've seen references to an anti-siphon vent, but I don't know what they do, and my other (professionally installed) regular AC system doesn't seem to have one)

THANK YOU!


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## supers05 (May 23, 2015)

I'd make an inverted style trap at the top to make sure that your external pump doesn't pump back into the unit. I put vents on my units. 

Below is a finger drawn sketch. Sorry for the quality, but it's difficult on a phone without a stylus. 










Cheers!


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## charliefreak100 (Jun 20, 2014)

Thank you! That's really helpful.

What is the purpose of the vent? If the condensate line gets blocked, won't the system overflow at the vent? 

Harry


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## supers05 (May 23, 2015)

Yes it will, but it won't drain well if you get air locks. I've had that before with just a simple 20ft drain hose to a floor drain. It'll drain, but will be much slower then your a/c is condensating. 

If you use 3/4" or larger hard pvc for the gravity drain, it's less of an issue.

PS. I leave some 4-6" for the top of the vent. It gives some extra room for error and easier to pour cleaner down the drain each season. 

Cheers!


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## cenfl (May 8, 2016)

Thank you... was wondering about the prospect of leaving the pump line open when using the gravity drain. I am going to stop up the pump line and simply use the gravity drain. Really appreciate the thread Harry and all the feedback/solutions here gentleman. Thank you.


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## cenfl (May 8, 2016)

One more question regarding this Mitsubishi unit.... I am using a remote thermostat so how to I wire in a drain pan alarm/shutoff on this unit? :vs_karate:


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## charliefreak100 (Jun 20, 2014)

I bought one of these:

https://www.acwholesalers.com/Aquag...0z1j1w5_0GacZK86L5RiFjGW3YR-flYmMlBoC_Fbw_wcB

It has a wire harness that links directly into the control board on the mitsubishi unit, so it will shut it off automatically. It was a breeze to install... only downside is the cost (at $50 it's expensive for a condensate alarm).

The control board has a header that governs shut-down so if you're electronically minded you can probably hook into that from a different unit. 

You could also get any condensate alarm that has an in-line switch, and hook it up on the power line from the external unit to the air handler.


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## supers05 (May 23, 2015)

If iirc, The Mitsubishi's have only one comms header. Make sure you get the AG-9300-MIT (or similar) instead of the universal as it has the 3 way wiring harness for it to work with remote stats. 

It's a bus topology, along with one wire being power. You could splice in and make your own wiring harness, but the above harness makes it easy

Cutting power to the indoor unit will give an "cannot communicate to indoor unit" error. Not the most intuitive when it does trip. 

Cheers!


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## cenfl (May 8, 2016)

Thank you... the fear of the over sophistication of this unit is beginning to subside, a little... hope it is really built to last since it will be a bear to try to get this back out of the ceiling :vs_karate:


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## charliefreak100 (Jun 20, 2014)

Ha! I know what you mean.

An HVAC pro who is a friend said they are built like tanks and just run and run so I'm hoping that's true. A nice big service hatch is also your friend!

Supers05... I was thinking about this unit for my external pump (the "mini" version):

http://www.aspenpumps.com/mini-a-maxi-orange.html

Any thoughts? I want a quiet pump as the unit is in a ceiling above an office space.

Thanks


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## supers05 (May 23, 2015)

We generally stay away from situations that require pumps in the first place. (planning with the drain in mind) When we do need to use a pump, we use the big classic condensate reservoir style pump. (tried and true, lasts about the same life as the unit.) 

I haven't used those particular pumps but have seen them in the wholesalers. Some contractors like them for their skim design. They require cleaning about twice a year though. (Much more sensitive then the big old bucket types.) 

Cheers!


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## charliefreak100 (Jun 20, 2014)

Any recommendations for more traditional reservoir type pumps?

Any that are a bit quieter than others?


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## supers05 (May 23, 2015)

This style will be slightly louder then the orange above, but we've used this in offices and haven't had complaints. There is a shallow pan version if required. 

http://m.homedepot.com/p/Little-GIANT-115-Volt-Automatic-Condensate-Removal-Pump-554401/204264949

Cheers!


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## charliefreak100 (Jun 20, 2014)

Thanks very much.

I was hoping for something that runs off 220V... I'll have to fish a wire for a 115 V unit. But it's good to know that those are reliable. (Cheaper too.)

Maybe I'll rig up some sort of sound damping e.g. acoustic tiles underneath the drain pan?

Thanks again for all your input


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## supers05 (May 23, 2015)

They are available in 220v. 

Cheers!


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## charliefreak100 (Jun 20, 2014)

Final question (I promise).

Do I need a trap on the condensate line? I can't imagine why I would (since it's not attached to a furnace, and drains into an open laundry sink) but I thought I should check!


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## supers05 (May 23, 2015)

You don't need a trap on the pump discharge line. 

Cheers!


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## cenfl (May 8, 2016)

Charlie, 

If you are going to use a pump, is there a reason you choose not to just use the onboard pump on the unit?

I just bought and connected one of these yesterday for the secondary drain pan which looks to be required by code. I connected to C20 two pin connector on the main board, which also had (REED) labeled on it with a connector in it which looks like it is a Thermistor?. The aquaguard sensor had an extra female plug on it that I assume I plug the existing (Thermistor?) connector into as it is now connected to the board? Couldn't find any instructions for that part of the install... :glasses:


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## supers05 (May 23, 2015)

cenfl said:


> Charlie,
> 
> If you are going to use a pump, is there a reason you choose not to just use the onboard pump on the unit?....


That was mentioned already. It leaves water in the drain pan. In places that humidity is a problem, this undermines dehumidification. 

Cheers!


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## cenfl (May 8, 2016)

Just wanted to add that one side of the unit (the side with the pump outlet) has the gravity drain at a significantly lower level than the other. So anyone for future use of the gravity drain, make sure to use the outlet below the pump for best drainage.

How is your unit working Charlie? Any issues??


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## cenfl (May 8, 2016)

Does anyone happen to know if there is a way to wire up a five wire thermostat to these units, or are we stuck using the Mitsu thermostat? :vs_karate:


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## supers05 (May 23, 2015)

They have a adapter module. It was posted on this site on another thread somewhere. I'll try to look it up. 

PS. The Mitsubishi stat is considered a communicating stat. Meaning that you'll be able to take full advantage of the modulation of the unit. The adapter allows for some modulation but you lose quite a bit. (less comfort) Their stats don't look too bad. They even have customized honeywell pro6000 versions. 

Cheers!


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## cenfl (May 8, 2016)

If can find adapter that would be excellent... I like the Mitsu thermostat though would like to have wifi control of the thermostat like my other units... Best of both worlds would be Mitsubishi thermostat with wifi capability  

From what I see there is quite a bit of functionality in the Mitsubishi thermostat that relates to the unit though I am not certain that I really even need to use any of it?

THank you,


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## supers05 (May 23, 2015)

Wi-Fi only (no wall stat except for remote included with one unit) 

http://innovations.mitsubishi-les.com/en/controls/wifi-adapter

Honeywell RedLink compatible stat. It's wireless, so you can place it anywhere within range. It's also able to work with the redLink internet gateway. The only catch is that it requires the gateway and hub sold separately. 

http://www.mitsubishicomfort.com/pr...reless-controller-to-residential-product-line

http://www.ecomfort.com/Mitsubishi-MHK1/p30825.html

https://www.amazon.com/gp/aw/d/B008...2&pc_redir=T1&redirect=true&tag=wwwtomkoom-20

There's one non-redLink version that has wifi built in but can't find it at the moment. 

Cheers!


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## cenfl (May 8, 2016)

Awesome man, tthank you,, 

Am I correct that the MELCloud wifi adapter is all I would need to use the android app to control the unit?

Will I still be able to use the wired Mitsu thermostat along with the app?

Looks like unit uses CN105 on the main board, is that going to be available or being used by another device by default.

Can't seem to find them for sale online anywhere...


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## supers05 (May 23, 2015)

There's only one plug on the board. Either the stat or the Wi-Fi module. That's the official line anyways. I've seen some references that you can splice it together and it works, but I have no hard evidence at the moment.

Anything connected to that plug can control the unit. The ir remote will also work along side those devices. (Of course that's only if the indoor unit came with one) 

Cheers!


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## cenfl (May 8, 2016)

Thank you, I'll look into making a splice harness and report back on results :vs_karate:


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