Replies

1. GBA Editor
   Martin Holladay | Jan 21, 2014 06:03am | #1

   Wayne,
   The two brands one keeps hearing about for cold climates are Fujitsu and Mitsubishi. I'm not aware of a Daikin model that performs well at very cold temperatures -- but I may be wrong.

   According to Dana Dorsett, a frequent commenter on this site, "I've heard from separate unverified internet sources that the Mitsubishi Hyper Heating units auto-stop around -19°F to self-protect, and re-start around -18°F, but that they DON'T in fact operate at -20°F & lower. ... I've also heard 2nd-hand reports of the Fujitsu RLS2s and RLS2-H continuing to run and put out a lot of heat at -30°F and below."

   Marc Rosenbaum, an engineer and energy expert, has written, "Recently it dropped to -5°F here on Martha's Vineyard, and my Fujitsu ¾-ton ducted unit was heating my basement (because the air handler is in the basement, and I haven’t got the ducts installed yet) and one-story house, a total of over 2,400 gross square feet, to 70°F. The load had to have been more than the published output of the unit at that temperature (14,000 BTU/hour). I was impressed. The best single zone systems have little drop-off in capacity down to 5°F. The cold climate Mitsubishi Hyperheats are rated down to -13°F and we’ve seen them running at temperatures below -20°F."

2. Expert Member
   Dana Dorsett | Jan 21, 2014 10:21am | #2

   Marc claims he has observed a Mitsubishi MSZ-FExxNA operating at -22F, and I''ll take him at his word, thus I'm becoming agnostic about the auto shut-down theory pending clarification from a more authoritative source than internet scuttlebutt (such as a Mitsubishi engineering source.)

   I've read several reports of Fujitsu AOU- xxRLS2, and AOU-xxRLS2-H putting out heat at outdoor temps below -25F. The -H version is the "XLTH" series, and has features for cold temperature operation that the non-H version doesn't have, eg: a pan heater to avoid the build up of ice on the bottom of the outdoor unit from defrost cycles, which has the potential to damage the fan blades. The rated output of the largest of XLTH series (AOU-15RLS2-H) at -15F (-26C) is 15,000BTU/hr, which is comparable to the popular Mitsubishi MSZ-FE18NA at that temp. The Fujitsu 1-ton puts out a bit more heat than the -FE12NA at low temps though.

   The Mitsubishis installed at a deep energy retrofit project I was involved with in Worcester MA (outside design temp = +5F) have performed flawlessly for the past 2 winters, the coldest temp experienced since they were commissioned was about -8F or -9F. They're fairly oversized for the tiny loads of that house- if they keep on going rather than shutting down for self-protection the place is probably good for -35F. (A temp probably not seen in that location since the last ice age.)

   SFAIK the lowest specified temp for any of the Daikin mini-splits is -20C/-4F. They still operate at lower temps, but at an unspecified output. I know of a Daikin Altherma (hot water output rather than hot air, but the same/similar outdoor compressor unit) installation in Maine at a location with a design temp of -8F or so that keeps on going at -15F (again, with unspecified output figures.) So, it matters what you mean by "cold climate", and the oversizing factor for dealing with temps below the lowest temp at which the unit has a specified-guaranteed output number.

3. 
   jinmtvt | Jan 21, 2014 10:40pm | #3

   I can confirm 9RLS2 putting heat at -32c ...may have hit a little colder..but i was sleeping then :p
   But when sub -25c temps, the output is really diminished... at 0c u can't stand in front of it ...at -25c it feels warm ..that's it.

   Also, that there was no ice build up wihtin any of the 4 untis i've monitored this winter,
   even after the very harsh and cold mid NOV to mid DEC we had.
   But a 12-14"" ice mound formed underneath one of the unit almost touching the bottom of the box.