Replies

1. Expert Member
   Michael Maines | Feb 22, 2021 10:07am | #1

   Joe, the disadvantages of ceiling cassettes are that they require a full 22 1/2" clear space, they need an access panel adjacent to the unit for maintenance, and they are not quite as efficient as wall-mounted units. With wall-mounted units you can direct the vanes to bounce air across the ceiling (the Coanda effect) which can help heat a room evenly; with ceiling-mounted units you don't have that option, but in an air-sealed, well-insulated house it shouldn't matter, and in a zone as warm as yours it's probably not important either. Personally I don't think they're much better-looking than wall-mounted units either, but taste is subjective.

1. 
   drafthunter | Feb 22, 2021 04:05pm | #4

   Interesting. Wouldn’t heating the ceiling leave cold air on the floor? I ask because have mistubishi units mounted high on the wall and my contractor said to point the vanes straight down when heating.

2. 
   averageJoe576 | Feb 22, 2021 06:11pm | #6

   Thanks for the info about the Coanda effect. So basically, for the same compressor, circulation/operating pressure is the key differentiator?

   I know the Fujutsu LZAS and Mitsubishi M-series also have very low min BTU which helps SEER as well, just not sure why they don't support ceiling cassettes with those compressors

1. Expert Member
   Michael Maines | Feb 22, 2021 07:09pm | #7

   Drafthunter, it depends on several factors, but the idea--which I learned from Cramer Silkworth, a mechanical engineer who trained me in Passive House design and sometimes posts here--is that vanes directed toward the ceiling will allow the heated air to "skip" along the ceiling, leading to evenly heated air. It works best in well-insulated and air-sealed buildings which have little temperature stratification, the term for warm air's tendency to rise. (It's a myth that "heat rises;" heat goes to where there isn't any, but warm, moist air is more buoyant than cool, dry air.)

   Others are probably more knowledgeable about the finer details than I am. Hopefully someone else weighs in.

2. Expert Member
   Akos | Feb 22, 2021 11:24am | #2

   There are one way and two way ceiling mounted cassettes that are better looking and narrower than the 4 way ones. Check out MLZ-KP12NA.

   If you have rooms in the place, there are also units that support jumper ducts to supply other spaces like:

   https://ashp.neep.org/#!/product/28903

   The knockouts on the side are for ducts, you can divert up to 50% of the flow to these, just take care as there is very little pressure available, so they must be large and mostly straight.

1. 
   kurtgranroth | Feb 22, 2021 02:35pm | #3

   A ductless mini-split with simple jumper ducts is a very interesting idea and also one that I had never heard of before. Can you point me to where I can read up more on this topic?

   I spent some time today trying to track down details on this but came up entirely empty. Even the LG LCN187HV docs that I could find make no mention of jump ducts. Yes, those absolutely do look like punch-out blocks but the PDFs I found never labeled them as such.

   So how would I find what units supported jump ducts? And are there docs on how these work?

1. Expert Member
   Akos | Feb 22, 2021 04:27pm | #5

   LG documentation is not the easiest to find, the one time I went down the rabbit hole with these, the only mention I found was that it was for distrubuting air within the same room and 1/2 the unit's flow. No other data.

   Search for "branch duct" here:

   https://files.lghvac.com/resources/EM_MultiV_CeilingCassette_IndoorUnits.pdf