We're trying to figure out where (if) we can put a FH9 mini split head here.  The trick is we have 92" (7'-8') ceilings on the 2nd floor.  The head unit is like 13" tall.    Even if we put it RIGHT up against the ceiling, it'd drop down to 6'7" height--a little close for comfort for me .  Assuming you had to give it a little room maybe 3-4" off the ceiling, it's even lower to potentially head banging heights if you had any little skip in your step. 

One thought I had was on the master bedroom over-stair closet wall , so you would be looking at it as you were heading down the stairs.  It would make for tricky condensate line and refrigerant lines since we don't want to bring it down the front of the house.

Any other options I'm missing?


Floor plan is here:

https://farm8.staticflickr.com/7490...29e6_b.jpg

Can you use any of the other heads that are available?

I'm open to anything although I admit I was fixated on the FH series since it's the most efficient with, I believe, the lowest operating temperature (or most output at lowest temperature).

It looks like the SUZ-KA09NA is an EnergyStar HSPF 10 unit that comes with a ceiling head (per http://www.mitsubishipro.com/media/...rguide.pdf)

From what I can tell, the COP @ 17F is only 2.45 on that one.  The COP @ 17F on the FH9 is 3.27.  So not an insignificant difference in efficiency.

The air enters the head from the top, blowing out the front.

Mounting it flush to the ceiling would be a performance disaster.

Read the fine-print on the +17F efficiency numbers on the submittal pages. The "Rated Capacity" is the modulation output level at which that +17F efficiency was measured. If the room/zone's heat load @ 17F is higher than the level at which it's efficiency was measured, your efficiency at that temp will be lower than advertized. If the room's heat load @ +17F is lower than the output at which they measured efficiency, your as-used efficiency will be higher than stated.


The KA09's rated capacity @ +17F is 6700 BTU/hr out of a max capacity of 7300 BTU/hr at that temp, which is the high end of it's modulation range:

http://www.mitsubishipro.com/media/289434/sez-kd09na-suz-ka09na_submittal.pdf

The FH09's rated capacity @ +17F is 6700 BTU/hr out of a max capacity of 12,200 BTU/hr at that temp, which is barely at half-speed.

http://usa.mylinkdrive.com/uploads/documents/4560/document/MSZ-FH09NA_MUZ-FH09NA_Submittal.pdf

At any modulation level a COP of 2.45 isn't terrible at +17F, but run the load calc at the temp to know if you will be doing better or worse than that number.

If the 99% design heat load is more than 1.5x the output of the head at that temp it starts to take a toll on efficiency too and at 2-3x oversizing that hit is significant. In those cases splitting the output from a 9K mini-duct cassette between 2-4 adjacent rooms with combined loads that add up to something around of the unit's output at the 99% outside design temp can be more efficient than a grossly oversized higher-efficiency head.

The SUZ/SEZ series dedicated single mini-duct units are better than most mini-ducted systems, and aren't much worse than the FE-series mini-splits (which have a pretty good track record.)

If the zone's heat load @ +17F is only 3000 BTU/hr, the FH09 is oversized by quite a bit for your 0F load and will spend most of the season cycling on/off rather than modulating. The KA09 would not be oversized, but would stilll probably cover you down to 0F (I'd have to look at the extended temp tables, but won't for just a straw-man exercise).

To know what's best here requires the actual heat load calculation numbers. The FH09 is still good for the full 12K down to +5F and will have more than 10K available at 0F.

What's your 99% outside design temp, and your approximate average temp in January (eyeball it with the cursor from a Weatherspark.com graph)? That would be the average daily temp, not the average high or average low.

Thanks for looking. The avg January temperature here (Warren, VT) is right about 17F (they have it listed at 16F here: http://www.weather.com/weather/wxclimatology/monthly/05674).

Here are some data points:
Floor 2 heat loss @ +17F is 5891 BTU/hour.
Floor 2 heat loss @ +5F is 7277 BTU/hour
Floor 2 heat loss @ 0F is 7854 BTU/hour
Floor 2 heat loss @ -4F is 8316 BTU/hour
Floor 2 heat loss @ -11F (99% design temp for Barre) is 9123 BTU/hour.

The FH09 would be appropriate, but only if you leave the doors open.

With the doors closed you can probably centrally locate a mini-duct cassette near the top of the stairs and split it's output between the bedrooms.

On page 26 are the heating capacity tables at 70F indoor temps for the SEZ/SUZ systems:

http://usa.mylinkdrive.com/uploads/documents/4297/document/17_8_SEZ_Ducted_Heat_Pump_Systems.pdf

The -KA09 would clearly NOT cut it! The -KA15 would have you covered down to about 0F, but the -KA18 would be more appropriate if you're hoping for it to cover most of the load at -11F.

At full blast at +17F the KA18 can deliver 13,100 BTU/hr so it would be running at about half speed to cover your ~6000BTU/hr at that load, with a higher COP than you would infer from the submittal's 13,100 BTU/hr for 1350 watts of power draw, which is about 2.8.  At half speed it should be doing better than 3.0, but probably not 3.5.

Curiously, the SUZ/SEZ KA15 has more output at +17F with a max of 13,700 than the KA15, but was efficeincy tested while modulating at 11,900 where it was drawing 1200W, a COP of 2.9.  At your +17F load of 5880 it would be modulating at half the tested speed and well under half it's max speed, also with a COP would also be north of 3.

Either would be appropriate if you can keep the duct runs very short and well balanced. The KA15 may even cut it down to -4F (unclear) but won't at -11F. If it's OK to lose a bit of ground (or supplement it a bit) at -11F it may be a better choice than the -KD18.

The specified low end of the operating range for these units is -5F, but it probably doesn't auto-stop, and will have crummier efficiency & capacity when operated below -5F outdoor temps.

We're really not big on closing doors... so I am OK with that.

Any thoughts on shoeing in the FH9 head unit on the stair closet wall - head unit would blow from top of stairs towards the tiny 2nd floor hallway as seen here:

https://farm8.staticflickr.com/7465...ea59_b.jpg

Our stairs would be ~40" wide... So it would be a very tight fit on the sides of the head , but here at least it would have plenty of room above the unit.

That sort of mount has worked at least once- if it fits, go for it!

You may have to play around with the positioning of the louvers a bit to get optional air spillage around the corner to the hallway to keep Bedroom 1 & Bedroom 2 tracking temp reasonably. The walk-in-closet may run cool (or not), but that's probably the room you care the least about.

So I just want to make sure that the FH15+FH9 is the correct decision here, rather than the FH15 plus FH12.

I'm also reconsidering putting both units on the first floor in opposing corners of the house due to tricky install location on 2nd floor.

FH9 rated output @ 17F = 6200 BTU/hour
FH12 rated output @ 17F = 8000 BTU/hour
FH15 rated output @ 17F = 11000 BTU/hour

My first floor + basement (unheated) @ +17F are 10336+2504=12890 BTU/hour heat loss
Second story is 5891 BTU/hour heat loss.
Total=18781 BTU/hour

So FH15+FH9 nearly gets me there, and FH15+FH12 has a little breathing room at rated capacity. Is it safe to say that if I go with the FH15+FH12 I'll get a better COP?


For -4F (82% of max power)
FH9 MAX output @ -4F = 9000 BTU/hour
FH12 MAX output @ -4F =11152 BTU/hour
FH15 MAX output @ -4F = 14760 BTU/hou

My basement(unheated) +Foor 1 heat loss @ -4F is 14666+3536=18202 BTU/hour
Second story is 8316 BTU/hour
Total 26518 BTU/hour (note these are Manual J numbers so, maybe a little fluffy)

Again, seems like the FH15+FH9 would nearly get me there, but would the FH15+FH12 give me a little more efficiency by modulating more at the lower temps? Obviously the FH9 and FH12 effectively cost the same to purchase and install. At warmer temps, I believe we can just shut 1 unit off entirely.

Am I putting too much emphasis on (probably slightly exaggerated) Manual J numbers?   With this winter, it definitely makes me think twice a bit about going light on the heat output on the low end of the temperature range. It's been in the negatives almost every morning for what seems like a very long time.   Coldest February on record so far in Montpelier, but it's not like January was warm.

If you size them to cover most or all of your load at your 99% outside design temp they will be modulating most of the season. Oversizing by as much as 1.5x has a neutral to somewhat positive effect on average efficiency. Even if your load calcs are overestimating by 25% there's no real down-side to upsizing the 3/4-ton to a 1-ton.

It's also looking to be record cold February for Worcester MA, and we're on track for a record seasonal snowfall year to boot. At 108" and counting Worcester is currently the seasonal snowfall leader among all US cities right now (but there is still time for others to catch up.) It's been pretty relentless, but last weekend's mere 5-6" gave some respite:

http://goldensnowglobe.com/current-top-10-snowiest-cities/

The prior record seasonal snow fall for Worcester was ~133" back in '96-'97, and we still have at least a couple months to go before the threat of snow has pretty much evaporated.

Until this season I had been recommending that people in central MA install the mini-splits 4 feet above grade under the protection of roof overhangs. The snow in my yard is currently about 5' at the eaves on my house (after shoveling off the roof to relieve the load), so I'm going to have to bump up the recommendation a foot or two. It's not clear that the peak snowpack depth is behind us yet.

You will get greater efficiency per ton than a traditional unit for sure. You might be surprised. I put in a 9k LG 27.5 seer in my living room on our first floor. The idea was to cut down on strip heat and allow control over the room we would be in the most. The result has actually been eliminating the use of the first floor 2 ton heatpump almost all together. I think since the end of January our first floor rheem has come on twice. The heat moves nicely and even the other side of the first floor is within the normal swing of what we use to keep the temp at. So in short the thing is doing what a 2 ton heat pump and 7kw heat strip was doing. Feb has had plenty of single digit nights. On one of them I measured the unit pulling 2 amps with a 70dec set temp inside.

Any thoughts on whether we'll be happy with a mini split on Floor 1 and Floor 2 (and nothing in the basement).   Not talking so much about hanging out in the basement, but will our feet be cold on floor 1?

Basement will be well insulated and sealed, but unheated.  It will have a heat pump hot water heater too.

We could always add a gas heater as basement backup.
Or install a heat pump in the basement and use gas to supplement upstairs.

I don't want to do 3x mini splits due to upfront cost and don't mind the idea of a gas heater as a backup that could run on minimal 120v power.

  Don't necessarily plan on heating basement to +65F if not necessary. 

Consider that if the basement is built and insulated properly, your temperatures there should be in the high 50's to mid 60's, so you will not need much energy to bring the temperatures up to comfortable levels.

Consider that if the basement is built and insulated properly, your temperatures there should be in the high 50's to mid 60's, so you will not need much energy to bring the temperatures up to comfortable levels.

Oh yeah - the basement heat loss at -11F should be around 3000 btu/hour. Maybe a little higher to offset heat pump HWH.

Do the Fujitsu's have remote thermostats available? Are they necessary?

Fujistu has remote thermostats compatible with most of their mini-splits. They're only necessary if the head is mounted in a location where the air-flow in the room causes it to short-cycle.

Without the wall -thermostat the room temp is sensed by the temp of the incoming air at the head, which isn't always going to be the average temp in the room, so there will be a temperature offset and occasional adjustments to the setpoint when running without the thermostat, but most people don't find that too big a nuisance. But if the thing is short-cycling due to rapid localized heating/cooling near the head, efficiency drops, and comfort does too, since the room temps won't be very stable.

Do any of the more/most efficient mini split options offer multi-heads per single outdoor unit?

I really like this RLS3H, and want to put one in for the main floor, but what would really be great is 1 more outdoor unit and 1 head in the basement and another head on the 2nd floor where the loads are relatively low. Total 2 outdoor units and 3 indoor. However I don't want to give up much efficiency or cold weather performance.  3 full units seems cost prohibitive for the minimal heat needed for basement and 2nd floor.

Yes. Mitsubishi started offering multi head hyper heat units in 2015.

Thanks.. Wow I didn't realize there was an FH18... for some reason I had only ever seen the FH9/12/15..  I thought the only 18 was the FE18. 

Still researching, but it doesn't look like the multi head units are less than each individual unit but there should be savings on installation.