Can mini-split line set be buried?

[joe_padavano]

I'm planning a multi-zone mini-split installation. This is a 300 year old log house, so there isn't an easy internal route to the farthest room (kitchen). The kitchen was an add-on and sits on a stone floor (no basement). I'm planning to use a floor-mount indoor unit in this room. The outdoor unit wants to be located at the opposite end of the house, near the panel box. The other two indoor units are both at that end of the house, so line set routing is easy.

Since there is no internal route from the outdoor unit to the kitchen, I want to run the line set in a conduit underground, around the outside of the house. Total length of this run will be on the order of 50-60 ft. The outside unit I'm looking at can accept a total line run to all units of 230 ft, which is much more than I will need. The buried conduit would be something like 2" PVC electrical conduit. The run is pretty straight with a right angle turn at each end.

I'd appreciate any thoughts on the viability of doing this. Thanks.

 

[rlitman]

I cannot imagine you being able to get a lineset through a conduit with any bends at all.
Nor can I imagine you getting a lineset through a 2" conduit. You MIGHT be able to get away with 3" conduit, IF it had absolutely no bends. And possibly 4" conduit, if the bends were gentle arcs kept down to a handful of degrees (NO WAY 90 degrees would work), and done with a heater.

But I would also worry about corrosion from the outside, if you bury the lineset.

 

[joe_padavano]

I cannot imagine you being able to get a lineset through a conduit with any bends at all.
Nor can I imagine you getting a lineset through a 2" conduit. You MIGHT be able to get away with 3" conduit, IF it had absolutely no bends. And possibly 4" conduit, if the bends were gentle arcs kept down to a handful of degrees (NO WAY 90 degrees would work), and done with a heater.

But I would also worry about corrosion from the outside, if you bury the lineset.

You are right about the routing. I did some more research after posting. Turns out that this is not uncommon, but as you correctly note, much larger conduit and more gentle bends are required. Turns out that at least one vendor sells an insulated copper line with an aluminum outer sheath that is designed for direct burial. Lennox's line set manual even talks about buried lines, so apparently it's done. Yes, there are design and implementation details that must be followed.

 

[txvwnut]

I would order the direct burial line set if you can. I've seen electrical conduit leach water no matter how well all of the joint connections are made.

 

[theoldwizard1]

I would order the direct burial line set if you can. I've seen electrical conduit leach water no matter how well all of the joint connections are made.

Yes, conduits leak. A line set is copper covered in an insulator. Wrap the whole thing in some kind of water resistant tape and bury it.

 

[joe_padavano]

I would order the direct burial line set if you can. I've seen electrical conduit leach water no matter how well all of the joint connections are made.

Yup. Now that I've found a vendor, that's definitely the way to go. Thanks.

 

[Jackfre]

I guess you can do it, but it would be interesting to see the temp of the individual lines entering and exiting the ground. I would have a chat with tech service at the company whose units you plan to install. Both the lines on mshp’s are gas lines as the expansion valves are in the condensing unit. I’ve done a lot of steam and hot water underground systems. Great care should be used to keep the interior of the conduit dry.

 

[Tracs]

I'm planning a multi-zone mini-split installation. This is a 300 year old log house, so there isn't an easy internal route to the farthest room (kitchen). The kitchen was an add-on and sits on a stone floor (no basement). I'm planning to use a floor-mount indoor unit in this room. The outdoor unit wants to be located at the opposite end of the house, near the panel box. The other two indoor units are both at that end of the house, so line set routing is easy.

Since there is no internal route from the outdoor unit to the kitchen, I want to run the line set in a conduit underground, around the outside of the house. Total length of this run will be on the order of 50-60 ft. The outside unit I'm looking at can accept a total line run to all units of 230 ft, which is much more than I will need. The buried conduit would be something like 2" PVC electrical conduit. The run is pretty straight with a right angle turn at each end.

I'd appreciate any thoughts on the viability of doing this. Thanks.

Would it not be easier just to run an electrical cable and mount the outdoor unit wherever you want? Why does it have to be mounted near the panel?

 

[joe_padavano]

Would it not be easier just to run an electrical cable and mount the outdoor unit wherever you want? Why does it have to be mounted near the panel?

Go back and read the part about it being a THREE zone system, and the outside unit would be mounted close to two of the three indoor units. No, I don't want a separate outside unit next to the front door...

 

[Climatecreator]

Ok assuming you ruled out using line hide run low on the outside perimeter walls? Sometimes they can be most cost effective and painted to hide or blend in along with landscaping.

Just throwing it out there because SOMETIMES you need to get at the lines or wire you run along with the lines for various reasons

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[Ed Devinney]

Climatecreator has a point, and maybe there is better than line hide. I lived 20 years in a 200+ y/o log house in NoVa, and think you have a few other options for running lines.

First option: run the lines bare against the logs, inside or out. The copper will take on a nice patina that goes well with the logs. We ran a bunch of 3/4" copper in the cabin, in the corners it will fade away.

Second is more work but will look very clean: tear out the chinking between logs and run through there, then replace the chinking.

A combination of these will probably get you where you need to go.

 

[joe_padavano]

Ok assuming you ruled out using line hide run low on the outside perimeter walls? Sometimes they can be most cost effective and painted to hide or blend in along with landscaping.

Just throwing it out there because SOMETIMES you need to get at the lines or wire you run along with the lines for various reasons

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That's the other option, and obviously I've considered it. Unfortunately the line would have to run right in front of a door with steps, so either it has to go up and over the doorway (which would be oh so attractive) or buried out in front of the stone steps. This is a 300 year old hand hewn log house. Nothing about it is conventional construction.

 

[joe_padavano]

Climatecreator has a point, and maybe there is better than line hide. I lived 20 years in a 200+ y/o log house in NoVa, and think you have a few other options for running lines.

First option: run the lines bare against the logs, inside or out. The copper will take on a nice patina that goes well with the logs. We ran a bunch of 3/4" copper in the cabin, in the corners it will fade away.

Second is more work but will look very clean: tear out the chinking between logs and run through there, then replace the chinking.

A combination of these will probably get you where you need to go.

First, the room that I'm trying to reach is a post-frame addition that's only about 100 years old. The transition from the original log house to this addition is not conducive to a direct run. NOTHING lines up, there is no continuous inside space or attic, no continuous basement, etc, etc.

Second, exposed lines inside or out are not an option, especially inside.

Third, tearing out the chinking is definitely not an option, since the whole inside chinking was recently repaired and painted. This it not a "gut the house" project. We're living in it.

I appreciate the suggestions, but trust me when I tell you that I HAVE considered all these options. There are no good ones. The location where the inside unit needs to mount is exactly on the opposite end of the house from where the other two inside units need to go.

 

[Trey T]

Never done it or ever heard anyone bury them. Keep in mind that the enclosed space (buried) will affect the thermodynamic aspect of the two pipes; therefore, it has to be isolated someway when it's bury to prevent unwanted heat transfer from one pipe to another, causing refrigeration process to go wacky.

The idea is similar to the NEC (electrical code) of only allowing specific wiring type in a conduit or raceway.

 

[Climatecreator]

That's the other option, and obviously I've considered it. Unfortunately the line would have to run right in front of a door with steps, so either it has to go up and over the doorway (which would be oh so attractive) or buried out in front of the stone steps. This is a 300 year old hand hewn log house. Nothing about it is conventional construction.

Then perhaps it's best in this application to use the multi zone at one end and a single zone at the kitchen. Is having two condensers a deal breaker? Far easier to run a long wire to another condenser from the panel than to do the lines under ground. They have so many ductless options out there that draw so little power it shouldn't be a problem. One company even has 110v condensers. Also having multiple units is sometimes good when one is down, etc etc.



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[joe_padavano]

Then perhaps it's best in this application to use the multi zone at one end and a single zone at the kitchen. Is having two condensers a deal breaker? Far easier to run a long wire to another condenser from the panel than to do the lines under ground. They have so many ductless options out there that draw so little power it shouldn't be a problem. One company even has 110v condensers. Also having multiple units is sometimes good when one is down, etc etc.

Go back and read Post #9:

No, I don't want a separate outside unit next to the front door...

As I've said above, apparently the buried line isn't a big deal and has been done to the point that direct burial lines are commercially available.

 

[Ed Devinney]

Sounds like you're all set, then.

 

[Climatecreator]

As I've said above, apparently the buried line isn't a big deal and has been done to the point that direct burial lines are commercially available.

You bet. Just thinking sometimes what's cheaper or easier overrides those initial thoughts.

I'm sure it'll work out for you underground as well.

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[joe_padavano]

You bet. Just thinking sometimes what's cheaper or easier overrides those initial thoughts.

I'm sure it'll work out for you underground as well.

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I appreciate the suggestions, and being lazy I'll ALWAYS try to find the path of least resistance. Unfortunately, not many options here.

 

[Ohmthis]

Joe, this get done more than you would think. Not every manufacturer has specs on how to do it with their equipment. It's best to call tech support for what ever company you plan to use. The direct burial is the easiest way, but 3" (minimum) PVC is used. Make sure to double insulate both lines, if you cannot find sweep 90s, then use 2 45s or the lines can/will kink. Primer and glue all joints, ease the lines in, use foam and mastic or caulking to seal it on both ends. Good luck, remember to take it slow when getting the lines in.

 

[joe_padavano]

Joe, this get done more than you would think. Not every manufacturer has specs on how to do it with their equipment. It's best to call tech support for what ever company you plan to use. The direct burial is the easiest way, but 3" (minimum) PVC is used. Make sure to double insulate both lines, if you cannot find sweep 90s, then use 2 45s or the lines can/will kink. Primer and glue all joints, ease the lines in, use foam and mastic or caulking to seal it on both ends. Good luck, remember to take it slow when getting the lines in.

Excellent. Thank you.

 

[brit vet]

Joe, this get done more than you would think. Not every manufacturer has specs on how to do it with their equipment. It's best to call tech support for what ever company you plan to use. The direct burial is the easiest way, but 3" (minimum) PVC is used. Make sure to double insulate both lines, if you cannot find sweep 90s, then use 2 45s or the lines can/will kink. Primer and glue all joints, ease the lines in, use foam and mastic or caulking to seal it on both ends. Good luck, remember to take it slow when getting the lines in.

Excellent. Thank you.

Ohmthis has it right but I would add: You can source the pipe work insulation in larger wall thicknesses – the usual being ½” but you can get ¾” or even 1”. If you can do the entire underground pipe run in soft coiled pipes doing away with any buried joints. Glue and tape the insulation joints so they don’t part as you could get condensation pooling in the PVC tube which will rot the insulation.

 

[joe_padavano]

Ohmthis has it right but I would add: You can source the pipe work insulation in larger wall thicknesses – the usual being ½” but you can get ¾” or even 1”. If you can do the entire underground pipe run in soft coiled pipes doing away with any buried joints. Glue and tape the insulation joints so they don’t part as you could get condensation pooling in the PVC tube which will rot the insulation.

Thanks. Good tips.

 

[cynthiavc]

Hi Joe, We are looking to do a mini-vac install on our elevated house (funky set up) and I am curious how your underground pipe install has turned out, 5 years later. Is it functioning well? Would you recommend this type of installation?

 

[LXCam]

If you do decide to use conduit they make long radius elbows. But most likely those will need to be sourced from an electrical wholesaler. Definitely not something Depot is going to carry.

 

[pcmeiners]

"an insulated copper line with an aluminum outer sheath that is designed for direct burial."

Perhaps in a desert, aluminum in moist soil reacts with minerals in the soil, will not work in the long term. As to conduit,it would not be that difficult with 4" pvc, with 90° sweeps instead of 90° elbows; you would need to lay out the conduit with all sweeps, but no joints connected, then carefully jockey the lineset thru the conduit and sweeps, only then gluing and connecting all the pvc. Removing insulation from a lineset is a really poor idea, as is letting the lineset insulation get wet in a conduit.

Just notticed Joe suggested sweeps previously.

Probably easier if you purchased flexible electric (completely non metal) conduit which would fit one piece of a lineset, so you would need conduit for each lineset member. I am sure you could get it in any length you want (without splices). Might cost more but it would be so much easier to run for burial

 

[LXCam]

"an insulated copper line with an aluminum outer sheath that is designed for direct burial."

Perhaps in a desert, aluminum in moist soil reacts with minerals in the soil, will not work in the long term. As to conduit,it would not be that difficult with 4" pvc, with 90° sweeps instead of 90° elbows; you would need to lay out the conduit with all sweeps, but no joints connected, then carefully jockey the lineset thru the conduit and sweeps, only then gluing and connecting all the pvc. Removing insulation from a lineset is a really poor idea, as is letting the lineset insulation get wet in a conduit.

Just notticed Joe suggested sweeps previously.

Probably easier if you purchased flexible electric (completely non metal) conduit which would fit one piece of a lineset, so you would need conduit for each lineset member. I am sure you could get it in any length you want (without splices). Might cost more but it would be so much easier to run for burial

Only since you felt the need to define it. In the trade the manufactures call them elbows.

 

[pcmeiners]

"In the trade the manufactures call them elbows."

At the parts counter you order sweeps, or long radius ELs or else your getting 90° elbows, at least in NYC.

 

[Lassen Forge]

We live in a 700 year old stone tower, and are having a 2 unit minisplit in the bottom and second floor with the ability to expand in the furue to the 3rd... the compressor/heat pump unit is going on the terrace on the 2nd floor, with lines going up and down... We have to be careful as out "city hall" (the comune office) in Assisi is a royal PITA and wants everyhing to look "authentic".... we're going with copper or copper-encased external lines (which they generally accept) to the bore hole in the tower wall, and then internally to their respective floors.

 

[PoorUB]

I have to ask if anyone commenting has actually pulled mini split line sets through PVC pipe?

I did a job a few years back the spec'ed the lines to be run underground and inside of 6 inch PVC. All I can say is, "it was a *****!". Keep in mind both lines of a mini split need to be insulated. The typical line set insulation doesn't pull through PVC pipe very well. The black foam doesn't anyway! Perhaps some of the newer covered insulation will. It certainly did not like to go around corners.

 

[pcmeiners]

"The typical line set insulation doesn't pull through PVC pipe very well."

That is why you run the lineset through the PVC and fittings before assembling them and gluing. Electricians have used the same method when running heavy cable.

 

[rlitman]

...The typical line set insulation doesn't pull through PVC pipe very well. The black foam doesn't anyway! Perhaps some of the newer covered insulation will. It certainly did not like to go around corners.

The insulation with the white plastic skin covered in pyramids pulls a lot easier.