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Community and Q&A

How to Seal and Flash Multiple Lineset Wall Penetration

rszimm | Posted in General Questions on

I’m leaning toward a Fujitsu 4 ton mini-split condenser with a series of 4 heads throughout the house.  I put a 4″ pvc penetration through my ICF before pouring for the linesets.  The thought was to have them all penetrate right next to the condenser and then route them inside the walls.  Now I’m a bit stuck on how to properly seal and flash the penetration.  All the dedicated flashings seem to be geared toward a single lineset.  I’ve been browsing around getting frustrated as no one seems to have a series of 4 coming through the same hole.

The exterior wall covering will be stucco.

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  1. rszimm | | #1

    Incidentally, I was on vacation in San Diego last week and saw the attached picture of a series of 3 line sets going into a stucco wall. Ugly as hell, but it probably keeps the rain out at least, and i guess they don't care about air sealing in San Diego. However, I have no idea what that recessed box is that they have there, or if there are better options

    Again, I'm hoping to find the best solution here. I'm getting a bit worried that my 4" hole isn't big enough....yikes...

  2. Expert Member


    You aren't finding dedicated flashing for multiple lines bunched together because it's seen as almost impossible to do well, so it is generally avoided.

    How big are y0ur linesets? Boring new holes with a hammer-drill and an appropriate sized bit should only take about five minutes each.

  3. Expert Member
    BILL WICHERS | | #3

    With multiple lines, about your only options are putty-type selants (duct seal, etc.), or canned foam. Canned foam will probably get you a better air seal, but it will rapidly deteriorate where it's exposed to sunlight. Duct seal will hold up better in the sun, but will never give you as good of an air seal.

    There aren't really any great ways to seal the lineset penetrations, unfortunately. You could possible use one of the multiple aperature cable seal grommets we have in the telecom industry for conduits in manholes, but I doubt you'd find the right size combinations.


  4. rszimm | | #4

    Malcolm, one lineset is 1/2 | 3/8" The other three are 3/8" | 1/4". But with the insulation those end up being 1-1/2" thick, so I guess I'll have to go rent a coring machine to make those sort of holes in the concrete if I go that way. Having to pop a bunch of holes will also not fit in well with the interior wall furring I've put in (picture attached), as the plumbing lines will get in the way, but I suppose I can route those around a different path.

    1. Expert Member
      BILL WICHERS | | #5

      You can get carbide masonry bits up to 1" or so for regular drills. I much, much prefer the SDS-plus bits for smaller sizes (up to maybe 1-1/8" or so). You can get big carbide bits up to close to 2" or so for the SDS max drills, but the coring bits usually drill more easily.

      If you have a lot of holes to drill in masonry, an SDS-plus drill would be a good investment. Once you've gone over to the SDS system, you'll never want to go back to a regular chuck again for drilling in masonry.


    2. Expert Member
      MALCOLM TAYLOR | | #6


      That's a lot bigger than I was envisaging. I'm not sure drilling makes sense. There has to be a better way to seal them in the existing hole. Hopefully someone with that knowledge will chime in.

  5. walta100 | | #7

    I can’t help myself, I got to ask the big picture questions.

    How sure are you that 4 tons is the correct size for your home?

    Are you sure you want the multi heads and a single outdoor unit?

    It is all too common to see mini split system bids that are so large they never will work correctly.

    Understand multi head systems never work as well as single head systems as they can’t slow down as much and you lose efficiency.

    Understand multi head systems any single part fails the whole system goes down.

    Understand sooner or later every system will leak with multi head systems have you searching a lot more connection when hunting for the leak.

    You may be surprised how little more 4 separate systems cost. asking for a bid cost you nothing.


  6. nhbean | | #8

    One suggestion I saw for flashing a lineset penetration on another post was to use a 4" dryer vent hood - just remove the screen and the damper flap; there's probably enough wiggle room to get your linesets through. The hood should help protect canned foam from UV exposure if you go that way.

  7. Expert Member
    NICK KEENAN | | #9

    Here's my suggestion:
    Two holes, one for all the liquid lines, one for all the suction lines. Take the insulation off for the width of the wall, and pack them in spray foam. Copper pipe in concrete should be sleeved in plastic so a 1-1/2" or 2" piece of PVC in an appropriate hole. I would seal the PVC in the hole with silicone. I'd bring the insulation up to the edge of the PVC pipe, and then wrap the whole thing in black foam insulation tape to tie the insulation to the PVC, cover any gaps, and protect the spray foam.

    Flash as you would a horizontal pipe.

  8. rszimm | | #10

    Walter, honestly I've been a bit concerned about sizing. During design I hired the premier HVAC firm here in Tucson to do a Manual J calc and size the system. This is what they came up with but I'm doing a bunch of things that simply don't get done here in the desert (e.g. ICF, full air seals, metal roofs, store front windows, ERVs, etc)

    It's a 2 story shop/guest house. The first floor is a walk out basement/shop, 1000sf and is ICF constructed with very few fenestrations, but a large (insulated) garage door. It gets a 12k BTU unit. The upstairs is standard 2x6 frame, also 1000sf, with a metric crap ton of windows (a bunch of storefront floor to ceiling). 12' ceilings, so a lot of volume. The roof is flat (i.e. no attic) with black standing seam metal, which means it'll get HOT in the Tucson sun, and the roof is only 12" thick, so I only have so much room for insulation. I plan to insulate as much as I can, and air seal up the wazoo, but there's still a lot working against me. It gets a ducted 2 ton unit and two 1 ton wall units in each of the bedrooms. Oh, and lets not forget that about 400 of the 1000 upstairs square footage is actually cantilevered and thus spanning clear space underneath, so it has exterior surfaces on 5 of its 6 sides.

    That said, it's a guest house and a workshop. If it's a little less efficient, it won't be the end of the world. If it breaks down and the whole thing goes offline, again, not the end of the world... I know the ideal is to size the system so it's on 24hrs/day on the hottest day of the year, but if I'm less efficient and comfortable I'll take it over more efficient but under-sized.

    Incidentally, I did see the attached image posted at another site. It seems to be similar to what a lot of you are suggesting. They have fewer linesets, but they filled the PVC with foam and capped the end with duct seal.

    1. Expert Member
      AKOS TOTH | | #11

      I've done multiple line sets exactly as the picture you attached. Seal with canned foam and cover the end with flex caulk to protect the foam from UV. Be careful when running that many lines through a wall like that, it is very easy to kink it.

      4 tons does sound a wee bit excessive for 2000sqft, surprisingly close to the usual 500sqft/ton rule of thumb, which feels like somebody didn't do their homework. Lot of glazing can add a fair bit of cooling load though if no shaded so it might be right.

      Either way, skip the wall mounts in each bedroom, these are a terrible idea for cooling (I have one and hate it) unless the bedroom is around 600sqft. Way too much airflow for comfort. Since you have a ducted unit for the main space, just connect the bedrooms to it. Saves money and you get a much better performing and comfortable system. It will also let you downsize the outdoor unit to a 2 or 3 zone, the more realistic size for a place like that is 2 to 2.5 ton.

      12" roof is plenty for insulation, even with a 2" vent channel, you can get a lot of fluffy insulation there, your heat gain from that roof will actually be pretty minimal even in your sunny climate.

  9. rszimm | | #12

    Gotta say, I really like DCContrarian's idea of separating the liquid and gas lines. That way you have like temperatures with like temperatures. Now that I look at the numbers, 9kBTU does seem oversized for a 180 square foot bedroom. The 7kBTU is probably still well oversized. I'm not certain that buys me much as it seems the 7kBTU and the 9kBTU units are pretty much identical (the low and extra low CFM ratings are identical, as are the cases, and the price is only $27 different). I wish I could duct in from the ducted unit, but it's just not in the cards. Flat roofs with zero attic don't give you a lot of flexibility on ducting, the framing is done, and putting in drop soffits in the living space is going to be an aesthetic challenge. (we just didn't design with them in mind). So maybe I'll drop the bedroom wall mounts to 7k, drop the ducted unit to a 18k, and see if I can get all that to run off their 36k condenser.

    I'm really seeing the benefit of the Mitsubishi system with the single line to the condenser and a multiplexer box mounted indoors. Unfortunately it priced out at around $2k more for just the hardware, so I guess I'll stick with Fujitsu...

    1. Expert Member
      AKOS TOTH | | #13

      I would look at installing a small ducted head just for the two bedrooms. The Fujitsu units can be mounted vericallly in a closet or a nook in the hallway with two very short runs to each room.

      This would let you drop to a 3 zone outdoor unit (cheaper) and save the cost of an extra head. This cost can buy a lot of ductwork plus you'll end up with a more reasonable matching to bedroom loads.

      The big multizone splits have very high min modulation, installing a small head on it can create issues as the load will be bellow the outdoor unit's min output. This either results in a lot of cycling or refrigerant bypass to other units
      Both are pretty bad for efficiency.

  10. omede-user-1113272282 | | #14

    Have you considered something like this?

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