Posted By cathsand on 22 Sep 2014 10:27 PM
...This house is going to have open cell foam in the 2x6 walls, .... It won't be code minimum R value. ...in the Atlanta area

Based on the 2012 IRC, R20 is the code minimum for 2x6 cavity insulation in zone 3 (Atlanta).  5.5" of R3.5/inch open cell spray foam with no exterior insulation wouldn't technically meet the code minimum but would likely be considered acceptable (just barely).

Odd, I thought it was R 13. Shows what I know.

Georgia building code for insulation is currently pegged to IECC 2009, not IRC 2012, which means code-min walls in Atlanta would indeed be R13 2x4 construction.

Most open cell foam is now rated R3.7inch, not R3.5/inch, to meet the  R13 code requirements for 2x4 construction, and would slightly exceed code min where  2x6/R20 is required.

Without a room-by-room Manual-J (that takes the mass effect of the SCIP fully into account) it's hard to say just what your heating & cooling loads will be.  Unless the Mitsubishi rep had referred to a real heat load calculation, calling for 7 heads would be little more than a WAG.

Energy Vanguard in Decatur would probably do a reasonable job on the load calculations- not sure if they have sufficient experience with ductless systems, but if you tell them your concerns about oversizing both the ductless heads and the compressors they will probably be scrupulous about really dialing in the true room loads rather than focusing primarily on the whole-house loads (the way you might with ducted heating & cooling systems, leaving the room-load issues for the duct designer to balance out.)  Make sure they understand how to adjust the U-factors for SCIP construction too- they may need to do a bit of head-scratching and research to get it right, but one of the owners has a degree in physics- he'll be able to figure it out.

It occurs to me that given these are mini-splits that you could put fewer units in and then add if more needed. Seems like no manual J has been done and someone who is really good, maybe the suggested contractor above could help.

Interested in what you decide to do and what systems are installed...

Posted By fun2drive on 23 Sep 2014 01:50 PM
It occurs to me that given these are mini-splits that you could put fewer units in and then add if more needed. Seems like no manual J has been done and someone who is really good, maybe the suggested contractor above could help.

Interested in what you decide to do and what systems are installed...

That would be fine in a retrofit where you are trying to displace some expensive heating fuel such as propane on a pre-existing & functioning heating system, but not in new construction. To meet code and get an occupancy permit you have to design the heating systems to be able to deliver at least 68F in every finished room of the house at the 99% outside design temperature.

Without the heat loss calculation it's really shooting in the dark. Most BTU/square foot rules of thumb approaches overestimate by 2x even when applied to code-min houses without any mass-walls.  The walls of this house are at least 30% better than code min, and if the windows & roof specs are proportionally better too the rules of thumb approach could lead to 3x oversizing.

I suspect the peak cooling loads on some rooms will be substantially higher than the peak heating loads, especially rooms with large west-facing windows.

You also need to know that some multi head systems need a minimum amount of load so you could be in a very expensive situation if not careful. Design on/with purpose makes more sense than trial and error.

I am looking at installing a 2 zone mini split system (one upstairs + one in basement). Does anyone have advice as to how I run the drain line of the basement mini if it is below grade? All info I keep seeing talks about how the drain from the head must 'angle down".

I'm the OP of this old thread, and happy to report that our minis are performing as predicted, or slightly better. With ICF walls, we can coast, sometimes for months at a time without using the HVAC. The basement ranges from 60 to 75 degrees, so we don't use HVAC down there at all.

Bobmane- They use condensate pumps for below grade installations. I believe it consists of a reservoir with a float switch and a pump to carry the condensate out.

bonmane: Mini-splits are usually overkill for the cooling & heating loads of basements (other than walk-out basements.) Has anybody done an aggressive Manual-J heat load calc on this?

What tips do you guys have on installing a mini-split on an interior wall?

Whats the question? we do that all the time. Somehow the lineset has to find it's way to the compressor - typically through the joists bay.

Thanks for reply bob, I just need to know tips for mini-split installation.

You will also need to find a way out for the condensate line ( gravity) or a condensate pump can be used , but the pumps have a high failure rate

Posted By Jennifer Thornton on 14 Aug 2017 10:48 AM
What tips do you guys have on installing a mini-split on an interior wall?

Dana1 ? Heatload on "this" basement? or as a whole?

in 55 degree soil (GTMUSING) the basements worked/installed, even with about one-third walk-out and about three feet above grade:

I.E.) 2004 Cools perfectly well on 95 degree days
and
 in 32 x 68 foot all open to registers...
 where they have basements decently insulated with a seal of quarter-inch foam (to one-half inch) with just standard R-11 batt results are such that only two ~ 140 cfm 12x4 ceiling registers adjusted to blow more-so downwards only to about a six-foot width of distributed air at an insulated concrete flooring (for heating primarily, in-flooring-radiant) with carpeting and a nice thick padding.  -family of 7 then-

GTmuse: 'merican is my first language, but I can't parse this post well enough to get anything but the vaguest idea of what you're asking/saying.