Replies

1. 
   mgensler | Sep 10, 2021 04:07pm | #1

   We're in zone 4 with a basement about the same size and similar construction. Our manual j called for the smallest system. We're putting in the 9k Fujitsu ducted minisplit which is rated even higher for heating. I think the 9k hyperheat ductless is rated for 12k of heat and will put out 15k or more in the moderate cold. Ask to see the calculations.

2. 
   kyle_r | Sep 10, 2021 04:33pm | #2

   The 9, 12, and 15k units all have the same minimum turndown. If it’s not a big upcharge you could go with the 15 to be safe. In your climate I would get the cold climate version.

3. 
   mgensler | Sep 10, 2021 05:47pm | #3

   The larger units are less efficient according to the specs.

1. 
   paul_iowa | Sep 11, 2021 06:39pm | #6

   The COP specs per NEEP are nearly identical for the rls3 9k, 12k, 15k as well as the lzah 9k, 12k and 15k. Yes, the HSPF ratings are marginally less the bigger you get, but you wouldn't notice a difference. I heat my one car wide garage shop with a 15rls3h and I love it.

4. 
   walta100 | Sep 11, 2021 11:43am | #4

   Consider do you need the mini split?

   The space is a basemen in a cooler climate my not need much if any cooling.

   If the basement is cool in the winter there is a 99.999% chance the boiler has enough excess capacity to easily heat the basement if you added some fin tube baseboard.

   If they do not show you the manual J it was not done. My wild guess rules of thumb says 9K will work just fine.

   Walta

1. 
   verm | Sep 12, 2021 01:42pm | #9

   I figured that the rule of thumb were these charts that are with several online articles on sizing a minisplit. 700 to 1000sq ft is a 18000. I just dont know if this includes basements with partial below grade walls.

   
5. 
   jason_v | Sep 11, 2021 01:16pm | #5

   I had several different manual J's done by mechanical engineers and they all came out wildly different. There are so many variables they have to "guesstimate" as to make them borderline useless (air infiltration, degree of shading etc so i decided to average them out and choose based on that.

   In my area the BTU output of the equipment i was choosing did not change the price (9K mitsubishi heat pumps cost the same as 12K)

   People talk with confidence about turndown ratios in minisplits but i found it almost impossible to find the information, and it changes when you have multiple units. I would not put faith in that they will turn down as much as your are lead to believe.

6. Expert Member
   Akos | Sep 11, 2021 07:59pm | #7

   The cost of the mini split install is probably comparable to installing rated rigid (ie Thermax) on the walls.

   Insulating the walls would reduce the heat loss to the point that the standby losses from your boiler will easily keep the space comfortable, so you are now heating this space for free.

   Most reasonably sealed and insulated basements in the summertime only need dehumidification, which even the smallest wall mount (ie 6000BTU or 75000BTU) unit will have a hard time doing without overcooling the space. Simplest is usually a reasonably efficient dehumidifier.

   P.S The important detail with rim joist is to air seal them, stuffing R19 batts in there helps a bit with heat loss but will do nothing for air leaks wich is the much much bigger source of heat loss. Air seal those areas properly. Simplest is spray foam, rigid foam pieces sealed in place with canned foam also works. The R19 batts can than go over the SPF or the rigid.

1. 
   verm | Sep 12, 2021 01:36pm | #8

   Hi Thank you for the info. I just finished my insulating the rim joists. I used rigid foam and spray foamed around them. Half of the rim joists will be unseen do to a drop ceiling. The other side exposed. Should i install drywall or wood paneling over them for fire code even though its just a game room? Ty

1. Expert Member
   Akos | Sep 12, 2021 08:13pm | #10

   I would check your local code. Most require a thermal barrier over rigid insulation exposed to the interior even if the space is unfinished, in my area this can be 5.5" mineral wool batt or 2" rigid mineral wool. Most drop ceilings are also not thermal barriers, so you need protection on that side as well.

   In your neck of the woods you can use dow thermax without any thermal barrier, which makes it a nice option when you want to insulate a basement but don't want to finish it. You can just glue it up on the foundation and tape the seams for a quick insulated basement.