Run refrigerant line inside stud bay on exterior wall?
We’re planning to install a minisplit system in an 1850s Greek Revival in Upstate NY, Climate Zone 5. The house was renovated in the 80s/90s with drywall and fiberglass insulation in the exterior 2×4 walls.
We want to balance energy efficiency with preserving the historic character of the outside of the house. To me, this means keeping line sets on the outside of the house to a minimum, especially on the front facade. (I know that line hide can be painted to match the siding, but the appearance still bothers me sometimes.)
We had a salesperson from a Mitsubishi HVAC installer visit the house to give us a quote. He said that if we put a wall unit on an exterior wall in each of the two big rooms on the first floor, we can run the refrigerant lines down through the stud bay into the unfinished basement, then across the basement to exit the back of the house. (There are layout limitations that make these wall positions the best choice in terms of air distribution, etc.)
I asked if we could also run the condensate line down through the same stud bay (parallel to the refrigerant line) and have it exit to the outside just above the foundation. The salesperson advised against this, saying that condensate should stay routed on the outside of the house.
Believe me, I don’t love the idea of ripping open a wall and displacing some amount of fiberglass insulation volume with a refrigerant line. That said, I’m wondering if it’s ever a justifiable choice, and if so, is it true that (1) also running the condensate line in the stud bay is a bad idea, and that (2) it’s only advisable to do this from a first floor (not a second floor), even in a balloon-frame house?
I’d appreciate any and all advice. Thanks!
Doug
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Replies
All of my refrigerant lines are inside the walls
I have too many windows, no exterior wall space, thus it is necessary
Be careful with drain lines, mini splits are fussy. It may be convenient to drain them to sewer if it is shorter.
Sheetrock/plaster is easy. Once you say that this is what you are going to do, it is no big deal
Pretend it is electric wiring, use nail plates
had to rerun a drain, takes about 4 years to rust a finish nail away.....
Great to hear. Thanks!
Nothing wrong with running lines in a wall especially if you are only going down. This is done all the time. You have to make sure the lines are fully insulated including where they pass through bottom plates otherwise the lines will sweat and cause water damage.
+1 on nail plates. Even better, use the heavy duty nail plates for CSST gas lines. One errant finish nail or drywall screw and you have a very expensive repair.
There is nothing wrong with also running the drain there, with an unfinished basement, running them to a floor drain is the easiest and keeps the outside of the house clean. Make sure not to use the corrugated pipe often sold with mini splits for the drains. I like to use either hard PVC pipe or black irrigation poly. Key to any drain is to always slope down, never have a droop in the drain anywhere.
Wall mount mini split drains tend to clog overtime (seems to be 2 to 4 years) so make sure the end is easily accessible to be able to clean it out with a shop vac.
Thanks Akos! That's very helpful.
Akos, a couple of follow-up questions have come up that I was wondering if you might clarify:
1. My understanding of nail plates is that they protect a refrigerant line (or wire or pipe or gas line) only at the point where it's running through a joist. Wouldn't the majority of the refrigerant line (running vertically down the stud bay) still be vulnerable to puncture? Say if someone wanted to drill a hole through the drywall into the cavity for inserting a drywall anchor?
2. Our 1858 house has sill beams with a cross-section that's ~8" square. My impression is that we'd have to drill some pretty big holes at a tricky diagonal through the beam to transition the insulated refrigerant lines and condensate line from the stud cavity into the basement. (See attached illustration for what I'm picturing.) Is this advisable? Even if we run the lines down the exterior of the house, if we want them to enter the basement, we'd have to either drill similar-diameter holes horizontally through the sill beam. Either way, I worry about removing so much material from an important structural element of the house.
You usually have less risk of puncture in the middle of the stud bay, since you don't usually have drywallers trying to put fasteners there (and those drywall screws are the most common cause of punctures in situations like this). For those lines though, you do want to secure them, even if just to prevent them from contacting the back of the drywall and transmitting noise and vibration. You can use horizontal blocking for this with holes drilled for the lines, or one of the support brackets made for the purpose.
Bill
Thanks Bill! That’s very helpful.
RE: sill beams
I would cut a corner and exit just under the floor rather than try to drill holes in the middle of a large beam. No point in making your life harder. A theoretically fully supported sill isn't doing much but I would still minimize what I was cutting out.
Provided there is no door or opening under the sill, you can notch it as suggest above. Make sure the tech is careful when running the line through to avoid kinking it.
Unlike where it passes through a stud, lines inside the stud cavity can move so it would be very hard to put a nail through it. It could still happen so something to watch if you are hanging something heavy there. The drill bit for an anchor is pretty big so it won't go through a floppy line in the wall but you can nick the 14/3 power feed to the unit.
Thanks Gus and Akos. I am picturing the abrupt ~90-degree turn the refrigerant and condensate lines will have to take from running vertically in the stud bay to running near-horizontally (still pitched down into the basement) for a few inches through the notch at the top of the sill beam / bottom of the floorboards. I hear what you’re saying about the risk of kinking, and I’ll admit I don’t have firsthand experience to know how forgiving these lines are. Also wondering if this tight situation means that flexible black irrigation poly would be preferable to pvc for the condensate line? Or should we just use pvc with an elbow fitting? The installer I’m talking to have initially said they won’t run condensate in the wall, but I’m trying to build a case for it.
Poly pipe doesn't carry the right fire rating for use inside the wall. You have to use PVC or CPVC if you want to go with plastic pipe here. I see no issue with a 90, aside from that being a potential clog point. You could braze 90s into the refrigerant lines if needed too.
Bill
Thanks Bill!
Doug-
I have an older house in Maine (also with 6x8 sill timbers). For our heat pump installation I also wanted to keep the historic charm of our house and minimize facade line-sets. Our "old" system was an oil fired steam boiler with one-pipe radiators.
At first, we received a couple of quotes- all for high-wall mounted air handlers, which also required more extensive exterior line sets. I've never loved the aesthetics of the high-wall mounted air handlers. They look OK in certain environments, but usually I'm not a fan of how they look in older homes.
I eventually "discovered" the floor (or low wall) mount units. I worked with a contractor to finalize the runs/locations to minimize exterior line-sets and to have a single hole to the exterior through the sill timber into our unfinished basement. The interior runs are simple straight shots to the indoor units where they go through the floor. It's a very clean install and all of the lines are visible in the basement and not buried in walls. The indoor units blend right into our home seamlessly. We're super pleased with our choice- both performance and aesthetic. Pic attached.
I'm passing this along just in case you haven't considered the floor units.
Best of luck.
That's really helpful, Steve. I have actually considered the floor units in the past, and shied away from them because it's a bit hard in our house to find the right layout when competing with furniture and windows. But I hadn't fully considered until your post how much cleaner the install would be. I'll give it some more thought. Thanks!