GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Samsung vs. Fujitsu Ducted Heat Pump

mibici | Posted in Mechanicals on

Hi Everyone. I’ve been perusing the site for a while now after purchasing a 1902 house in northern coastal CA (Eureka) a year ago. I appreciate the wealth of knowledge and free flow of information here.

The house is well built but in need of a lot of work. We’re trying to do a lot all at once, so have multiple parallel projects ongoing, including solar, mechanicals, weather sealing, crawl space encapsulation, landscaping and interior bathroom/kitchen renovations.

We have seized on an opportunity through our local electric utility to install solar and be part of a community solar grid. The solar system (17kwh) is being installed this week, and will allow us to sell energy back to the grid. We are using this shift as an opportunity to decarbonize in an economical manner and so will be replacing an old gas furnace and old gas water heater with heat pumps. After that I will be encapsulating the crawl space.

My question is regarding hvac system options. The house is single story, 1500 sq ft, 3B2ba, original single pane sash, post on pier construction, over a skirted crawl space, with a large attic. It is currently poorly sealed, but I will be working over time on sealing it to Pretty Good House levels, including air sealing, crawl space encapsulation, exterior storms on original windows, insulation in some walls that are currently down to studs, and maybe one day exterior insulation/air barrier and rain screen when we replace the asbestos siding. Our climate is cool humid, with really no need for cooling. It rarely gets above 73F, and rarely below 40F. 99% heating temp is 28F. Humidity and mold are an issue in general around here. We will also have an efficient Blaze king stove insert for auxiliary heat.

I am in discussion with a local hvac co about the installation, and he is recommending a 3 ton Samsung ducted system with a multi position air handler.  Model #:
AC036BXADCH/AA outdoor unit. Ac036KNZDCH/AA indoor unit.

I have heard good things here about the Fujitsu ducted mini split systems, and he says he can do a Fujitsu system for the same price, but is not a dealer for Fujitsu so is less knowledgeable. I’m not sure what Fujitsu model he would spec, but I’ve been looking into

  • For Single Zone (AOU24RGLX)
  • (1) Fujitsu – 24k BTU – Multi-Position Air Handler – Single Zone (AMUG24LMAS)

Or

ARU24RGLX with AOU24RGLX

Given all of that, is there any benefit to Samsung over Fujitsu or vice versa? (Mitsubishi is out of the question due to King lead times)

Thanks so much for your advice
-Sean

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. twoodson | | #1

    Your system sound extremely oversized at 3 tons. The 2 ton Fujitsu has a good turn-down ratio if that fits the bill, so over sizing might be less of an issue. (I have two of those and they are fantastic.). I wouldn’t be surprised if the 1 ton mid static Fujitsu would be appropriate in your climate. The output at your design temp is probably higher than the rating of these systems. Just checked the design manual and it outputs 19kbtu at 32 degrees. Oversizing to extremes reduce comfort, efficiency and the longevity of your equipment as it must cycle to meet the load and is less efficient at the lowest outputs.

    https://portal.fujitsugeneral.com/files/catalog/files/(D&T)%20ARU12-48RGLX.pdf

    You might want so do a quick manual j. You can use coolcalc to get close. If you know your gas usage, you might also be able to estimate your 99% load. There are a few great articles at GBA on how to do that.

  2. mibici | | #2

    Thank for the reply. That is in line with what I was thinking as well, and I do plan to talk him into a more appropriate sized unit. I used one of the online tools, not a strict Man J calc but a tool that Dana had posted, and it suggested a 2 ton system, so I think that will be the max I would go for, especially with the wood stove.

    I've looked into doing a gas usage estimate, but the issue with that is that we have only been heating the house to a bare minimum, as we are living in the shop while doing renovations on the house, not to mention that a few walls are down to studs and some floors down to the subfloor, so there is no way it would be accurate.

  3. twoodson | | #3

    You may be able to get the previous owners gas usage from the utility company. We can in my state. Remove the average gas usage during non heating months to zero out your dhw usage.

    As for usage, with your stove and planned improvements, you might target the equipment size for the post-improvements load so the past usage may be irrelevant.

    For what it’s worth, I’m heating a 3200sqft 1905 brick building with 2x 2 ton units. My design temp is 8F. Not a lot of insulation either. Manual J is rather conservative.

  4. mibici | | #4

    Thank you Tom. I think that with the upgrading that we’ll be doing, the previous usage won’t be so relevant, except maybe to set an upper limit of the new system or prove to the contractor that we can get by with a much smaller system. In any case, I will be pushing for a 1.5-2 ton system.

    Now, anyone with thoughts or experiences with Samsung vs Fujitsu for the proposed system?

  5. Sofiane | | #5

    What system did you end up choosing?

  6. Expert Member
    Dana Dorsett | | #6

    Even a 2- tonner is going to be WAY oversized for the "after upgrades" picture, and is probably oversized for the house where-is-as-is.

    A 1500' circa 1900 house with low-E storms over reasonably tight wood double hungs, insulated & sealed to pretty-good-house levels would have a likely design heat load of <10,000 BTU/hr @ 37F, Eureka's 99% outside design temp, and given the relatively small window/floor ratio of the era, and an even LOWER design cooling load at 66F (Eureka's 1% temperature bin.) If you don't believe it, run a load calculation using the BetterBuiltNW HVAC tool (it's quick & easy to use- even HVAC contractors can follow it! :-) )

    https://betterbuiltnw.com/hvac-sizing-tool

    You have to sign up and share your email, but the tool is free.

    A modulating 1.5 tonner wouldn't be a disaster, but a 3/4 or 1 tonner would be a better fit. eg: The 3/4 ton Fujitsu -9RLFCD slim duct unit can push well over 15,000 BTU/hr of heating @ 37F, and over 14K of cooling @ 66F:

    https://ashp.neep.org/#!/product/25310/7/25000///0

    There are others.

    Well before you hit PGH levels of retrofit the loads of that house are going to fall within those ranges. In fact, with just some air tightening (particularly at the floor, given the pier foundation, not just the attic & walls) and some tight storm windows it's probably already there with huge margin, though it's still worth tightening & insulating.

    The -24RLGX is a beast- it can probably heat your house as-is when it's 17F outside. It can easily heat my 1920s way-below PGH (or even current code) 2400' fully above grade + 1600' insulated basement 1.5 story house at 37F outdoors , and would even keep up just fine at +20F outdoors:

    https://ashp.neep.org/#!/product/25350/7/25000///0

    If your contractor is willing to quote the 1-ton -RGLX paired (rather than deal with designing ducts for a l0w-static air handler) paired with the 12RLFC compressor it's probably not a disaster:

    https://ashp.neep.org/#!/product/25349/7/25000///0

    The AC036BXADCH is even beastlier, and could easily heat my house at +10F.

    https://ashp.neep.org/#!/product/56510/7/25000///0

    My recommendation would be to run the actual load numbers of the "before upgrades" and "after upgrades" version of the house, and pick something appropriately small, even if it can't keep up at the "before upgrades" version of the house. Bigger is the opposite of better when it comes to heat pumps, even if you have to burn some auxiliary heating strip for a few 10s of hours in the early years as you are tightening the place up.

    And, run the ducts in the crawlspace under the floor, (even if it's open piers right now) not up in the attic where they would be subject to higher parasitic cooling & heating loads.

    1. Expert Member
      Dana Dorsett | | #7

      FWIW: Late last year I specified a heating solution for a retiree living in an ancient ~900' double-wide mobile home near Bremerton WA (heating design temp ~+25F), with at BEST R6 in the walls, though (according to the homeowner) the windows had all been replaced with something U32-ish about a decade ago. Like a pier foundation house it's pretty breezy under the floor even with skirting, and there may be some wadded up R11s under the floor (didn't do a site visit, but heard the description over the phone.) That place is 40% smaller than yours, but probably has comparable or bigger 99% heat loss numbers as your place due to the thin insulation and a design temp a good dozen degrees cooler.

      After running the load numbers the solution settled on there was a 1-ton cool climate Daikin wall type minisplit (https://ashp.neep.org/#!/product/56996/7/25000///0 ) good for ~16,000 BTU/hr @ 25F in the open main living/dining/kitchen area, and a 600 watt (~2000 BTU/hr) ceramic panel radiator to cover the master bedroom & private bath at the other end of the house. That's only ~18,000 BTU/hr total, but the mini-split is right-sized and will modulate rather than cycle on/off for most of the heating season, and even when it's +10F outside (happens in that location, if rarely) the panel-rad will keep the master bedroom warm despite being doored-off from the main zone. Depending on just how close I was on guesstimating the air leakage numbers the Daikin will likely still be keeping up at +10-F too (TBD), but it will for-sure be keeping up at +20F.

      With a large picture window on an un-shaded southern exposure the cooling loads are big enough to warrant the 1 ton, given the recent summers' 100F+ heat wave, otherwise the 3/4 tonner in that series would have been enough.

      This all to point out that heating loads of even pretty poorly insulated houses are lower than most people think. If you're not running the load numbers using fairly aggressive assumptions it's way to easy to end up oversizing it, often by a lot. Given the size of the house, the outside design temps in Eureka, and your weatherization plans the proposed equipment is simply ludicrous, probably the result of somebody's lousy " xxBTU/square foot" or "a cooling ton per xxx square feet" type rule of thumb with a bit added on "just to be sure", which is close to the WORST possible way to size a heat pump.

      A house built in 1902 most likely has full-dimension 2x4 stud bays, which if not already insulated could for low money be filled with blown cellulose, improving both air tightness and conducted losses to bring it with range of a 3/4 ton or 1-ton ducted Fujitsu, and that can happen long before taking the bigger money steps bringing it to Pretty Good House levels. From a bang/buck point of view, air sealing the floor & attic floor is job # 1, air sealing the walls is #2, followed by wall/floor/attic framing insulation- get the cheap stuff taken care of first.

  7. Danan_S | | #8

    I'm in coastal Northern CA, with a similar season temperature variation to your area.

    Adding to the chorus of folks suggesting your system might be oversized, I'll provide you with my anecdote which might be a helpful concrete data point.

    When I recently remodeled our 1600sqft house to somewhere between a Pretty Good House and a Passive House, we installed a Fujitsu ducted heat pump (https://www.fujitsu-general.com/us/resources/pdf/support/downloads/submittal-sheets/current/12RLFCD-2019B.pdf) that outputs 1.5 tons for heating, 1 ton for cooling.

    Despite my spouse's extreme sensitivity to cold, that was more than enough capacity to keep her comfortable this past winter.

    So my experience corroborates Dana's point above about how 2 tons itself might even be excessive.

  8. mibici | | #9

    Thanks so much or your expertise and insight Dana. I have plugged some numbers into the Better Built calculator and, depending if I choose 2x4 poorly insulated or existing poorly insulated, the heating load prior to upgrade is between 34,000 and 42,000 btu/hr. When I model the post upgrade scenario, I get between 10,000 and 16,000 btu/hr.

    Those seem like reasonable numbers to me. In discussion with the HVAC contractor, he is willing to put in a 2 ton fujitsu system (but he doesn't recommend it). With the spread of the house and need for reasonably long duct runs, and with a fair amount of space in the crawlspace, he is suggesting a multi position air handler. The Fujitsu AMUG24LMAS seems to offer a pretty good turndown ratio, with a low output setting of 5,400 btu/hr. With this air handler, it seems as though we could run on low for most of the time, avoiding short cycling, and have the capacity for most if not all of the coldest days, even pre weatherization. I think the contractor would lose his mind if I suggested a 3/4-1 ton system at this point, although I see the logic to it.

    With regard to weatherization plans, once we have some of the interior issues taken care of, my priority will be on air sealing the ceiling/attic, air sealing walls, and encapsulating and conditioning the crawl space. Although a quick and relatively cheap blown in cellulose insulation in the walls sounds appealing, I'm worried a bit about the moisture effects in this climate and the potential for rot given that the house was built without sheathing or a rain gap. The siding is simply against the studs. In the mudroom and bathrooms where we have exterior walls down to the studs, I am planning to put furring strips to create an interior rain gap, and use cut and cobble foam and rockwool before putting drywall up, but that is a small portion of the entire house.

    Over the long term, I would like to remove the asbestos shingles that were put over the original siding, put up plywood sheathing, insulate and air seal from the outside, and reinstall the original siding (or period appropriate replacement) over a rain screen. That will likely take a decade, however, if we can ever make it a priority.

    Thanks again for all your help. As of now, the contractor and I have tentatively agreed on the Fujitsu 2 ton multi position air handler. If you think that system would be a terrible idea, I would reconsider, but if you think it would be an ok fit for the proposed plan, then I will move forward, as it is likely the most aggressively sized system that contractors around here will spec.

    1. twoodson | | #10

      I have that exact unit. I will say, if your contractor will go for the mid static versions and it fits your space (I also have that one), the indoor for unit is higher quality; designed and built by Fujitsu. The multi position is rheem I believe, it’s not bad, but not in the same class. A well designed duct system can easily be serviced by the mid static; mine has 3 bedrooms, 2 bathrooms, 2 large corridors, a kitchen, a dining room and a living room (~1800 sqft). Just make sure they actually do a manual d for sizing. Both the mid static and the multi position use the same outdoor unit, fwiw.

      1. Sofiane | | #12

        Can you provide more details about your setp up: Is your house on one or two floors? And where is you unit located?

        Thanks!

        1. twoodson | | #13

          Two floors. Separate apartments. Mid static upstairs. Multi position downstairs.

          Both outdoor units are on the roof (low slope).

          Zone 4a, 8f 99% design temp.

  9. mibici | | #11

    That’s great to know, thanks Tom! I’ll look into the possibility of a mid static unit and pitch the idea to them.

  10. mibici | | #14

    I'v taken some time to run the numbers on a variety of different options, and coming away with a few different ideas in mind. I would love the groups opinion on these different models.

    When I run the numbers from BetterBuiltNW (with 18,000 btu/hr load suggested after moderate/reasonable weatherization) and model the different options for heat pumps using ASHP, it appears that the unit that best fits the house needs are the ADUH18LUAS, which would not need supplemental heat and only 2.7% annual low load cycling. The next best was the ADUH12LUAS, with the same annual low load cycling, but 0.7% supplemental heat use.

    The ARU18RLF model covers all the expected heat, but with 5% annual low load cycling. The ARU12RLF would require 0.4% supplemental heat, but the same 5% low load cycling, so doesn't appear to be much benefit.

    Of the medium static units, the ARU12GLX would require 0.4% supplemental heating and have 5% low load cycling. The ARU18GLX seems like a decidedly worse fit, with no supplemental heating required, but with a whopping 22% low load cycling.

    It appears that the low static units, particularly the ADU18LUAS, would be a better fit for the projected heating needs of the house. This raises the question of whether a low static unit would be sufficient for our house? The low static Fujitsu units have 0.36" WC, compared to the 0.8" WC for the mid static units. How could I easily determine the static requirements of the house?

    Thanks,
    Sean

  11. mibici | | #15

    An update to the last post... After running those numbers and pitching the idea of the ADU18LUAS to the HVAC contractor who was all set to install a 2 ton system, he replied that he already felt like the 2 ton was undersized and didn't feel comfortable going any smaller. With the real world examples that you all have provided, and the modeling to suggest a 1-1.5ton system is appropriate, I didn't feel comfortable signing up for an oversized system that we'd be stuck with for 20+ years, so we agreed to part ways.

    So, I'm on the lookout for a contractor who would be interested in installing a 1.5 ton fujitsu system in the Eureka/Arcata/McKinleyville area, if y'all have any leads...

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |