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New construction HVAC options

dirtriding4life | Posted in General Questions on

I’m a new member here looking for some advice on a my new home. I’m in Central Oregon which is climate zone 5B and the home will be a 1552 sq ft single level open floor plan all electric house. It is part of a small subdivision and the builder is being very flexible with options. Our 99% design conditions are a low of 4* and high of 87* with low RH. I’ve tried my best at a manual-j online and have gotten about 17,000 btu for heating and 15,000 btu for cooling. The great room has a vaulted ceiling and the rest of the home is 9ft. The home is situated with the long exterior wall of the great room facing south.

This is a budget build am hoping to make the home as efficient as possible to heat and cool with possibly treating the great room and bedrooms as two separate zones.

Factory option. The home comes standard with a wall mounted 1.5 ton Mitsubishi hyper-heat model in the great room aimed down the hallway and electric resistance heaters in the bedrooms and bathrooms. My concern with the standard design is the bedrooms becoming cold at night with doors closed and needing to rely primarily on the resistance heaters. Also, I see the lack of cooling in the bedrooms as a downside.

Option 1 +$4560 quote. My original idea was to downsize the wall mounted unit in the great room and install a horizontal ducted unit in the attic above the hallway with short duct runs to each of the three bedrooms and leaving electric resistance in the bathrooms (code requires a second heat source). As I’ve done more research I’ve learned that doing this will break the thermal envelope and drops the efficiency. Would doing this and insulating the ducts with closed cell foam be a good option?

Option 2 + ~$5,000. The HVAC professional mentioned that we could omit the ductless unit and install a traditional heat pump forced air unit for close to the cost of option 1. Upgrading to a dual stage unit would be higher cost and an option I would likely choose. My current rental has an oversized forced air heat pump and the constant on, off makes me crazy. As I’ve learned more about mini-splits I’ve been more interested in their efficiency and quiet always modulating performance.

Option 3. Anyone have any ideas?

Thank you for your help to keep my family comfortable for years to come.

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  1. user-2310254 | | #1

    Is your builder using roof trusses? If so, maybe he/she could install a plenum truss, which would allow you to run ducts (conventional or mini split) and still keep them inside the conditioned space.

  2. Expert Member
    Dana Dorsett | | #2

    A 1.5 ton mini-ducted Fujitsu 18RLFCD has sufficient capacity to cover your load, delivering more than 18,000 BTU/hr even at -4F.

    That unit has a beefier blower than most Mitsubishi mini-duct cassettes, but Fujitsu has an even beefier cassette that works with even hack rules of thumb duct design HVAC contractors use for "full sized" air handlers:!/product/25348

    While they have cold-climate type compressors, the Fujitsu mini-ducted units don't have a pan heater to automatically manage defrost ice. The wintertime dew points in central OR in winter are low enough that it's probably not a big deal run it without a pan heater, especially if your daily high temps are usually north of freezing the way it is in Bend:

    Midea has a comparable, full-on cold climate 1.5 tonner (with the pan heater) worth considering:!/product/26536

    The price point on Midea (a first-tier Chinese company) is usually cheaper than the Japanese vendor equivalents. About a decade ago Carrier got into bed with Midea, and is selling a lot of Midea product under the Carrier nameplate, including that 1.5 ton cold climate mini-ducted version:!/product/26449

    It's the same product under the label, but the price and support chains would be separate.

  3. walta100 | | #3

    Whatever you do keep the ducts out of the attic and inside the conditioned space. Just say no to stupid, it is harder than it sounds as stupid is so common.

    You house seems like a good fit for a ducted mini split. The problem will be finding a contractor to install one without oversized it and designing the ductwork with a computer model.

    Very few HVAC contractors are sold on mini splits and only a small percentage of that small percentage like the ducted minis.


  4. vashonz | | #4

    I can't quite read the plans but looks like its in Tumalo? I'm pretty sure the design temp is 12°F.

    I personally would choose the "factory" option, it's basically what I'm doing (1300sqft, all electric, mini-splits, in Terrebonne), both of the alternatives seem to add ducting in a potentially unconditioned space.

    If they're planning on an 18k unit, thats great. The HVAC contractor was adamant I have a 3 head, 36000BTU multisplit, for a 1300sqft house, and for some reason used a 0°F design temp. I'm doing 12k in the main room, 6k in the master bedroom, and resistance in the entryway and 2nd bedroom.

    With that said, Dana is wicked smart, I always like to see his thoughts on different options.

  5. StephenW81 | | #5

    Dana said: "While they have cold-climate type compressors, the Fujitsu mini-ducted units don't have a pan heater to automatically manage defrost ice. "

    That seems like a potential (if occasional) problem; given that they are rated to -5F, I didn't anticipate that. I wonder how Elden Lindamood's Fujitsu slim duct unit is working in northern Minnesota without pan heaters? Or am I misunderstanding that xxRGLX does not have a pan heater whereas the xxRLFC does?

    Interestingly, it looks like if you go with a muiltizone system, you can get the XLTH low temperature compressor with slim duct indoor units. What would be the drawbacks of an 18k btu multizone system with two 9k btu slim duct indoor units?

    1. Expert Member
      Dana Dorsett | | #6

      >"Or am I misunderstanding that xxRGLX does not have a pan heater whereas the xxRLFC does?"

      Neither of those Fujitsu series has (or supports) pan heaters. There aren't enough data points out there to determine how big of a problem that will be in colder locations like northern MN, but in a high dry central OR location with a 99% outdoor design temp in positive digits F like Bend my expectations would be that the risks are quite small. The latent loads in summer are steeply negative, and when it's actually +4F in central OR the amount of moisture in the air is pretty low. It doesn't stay that cold for weeks on end in that area the way it does in northern MN, where the mean outdoor temperature in January can be in single digits:

      In central OR it very rarely goes a week without breaking the freezing point for a stretch of consecutive hours, whereas that's common in the upper midwest. It usually takes quite awhile to build up much defrost ice in the pan- in central OR it's dry enough that snow can slowly disappear via sublimation during cold weather.

      >"XLTH low temperature compressor with slim duct indoor units. What would be the drawbacks of an 18k btu multizone system with two 9k btu slim duct indoor units?"

      The minimum modulated output of the -18RLXFZH multi-split much higher than the single zone systems, twice that of the -18RLFCD, if only somewhat higher than a single zoned Carrier/Midea 40MBDQ18---3 on a 38MAQB18R--3 compressor. The -18RLXFZH also has a lower HSPF efficiency than the single zoned ducted options (even when running with ductless heads).!/product/25328!/product/26449

      If you're on the natural gas grid there is probably a Dettson solution that would right sized, though going all-electric with right-sized (and modulating, if possible) heat pumps would still be the better option.

  6. alan72 | | #7

    Dana - is there a quality difference between the Fujitsu and Mitsubishi ducted units - longevity/need for repairs/etc?

    Do the Fujitsu ducted units perform better due to the higher static pressures?

    Can u retrofit a pan heater to those units that don’t have them?



    1. Expert Member
      Dana Dorsett | | #9

      >"- is there a quality difference between the Fujitsu and Mitsubishi ducted units - longevity/need for repairs/etc?"

      Not that I'm aware of, but I have too few data points to really guess. Check the details on the warranty stuff- sometimes there are longer warranties when installed by people with higher levels of factory certified training.

      >"Do the Fujitsu ducted units perform better due to the higher static pressures?"

      The higher static pressure capability means you can get away with somewhat skinnier ducts.

      The other advantage Fujitsu has over the competition is that they can be mounted vertically in a tiny sub-10 square foot "utility closet", whereas most need to be mounted horizontally.

      >"Can u retrofit a pan heater to those units that don’t have them?"

      There is no automatic pan heater control, but creative people with basic electronic/electrical design skills have come up with various hacked-in retrofits to deal with it. The crudest/simplest would be a heat tape of about the right wattage mounted to the underside of the pan to be plugged in manually if an ice plug forms in the pan drain.

      The Carrier/Midea defrost pan heater control algorithm is better than most:
      1.When the unit power on and changed in heating mode,and if the outdoor temperature continue lower than 3C for 30 seconds,after running for 25mins, the base pan heater will be actived for 5 minutes.

      2.If be on the defrost mode and the outdoor temperature lower 1C for 10 seconds the base pan heater will be actived and will be 5 mins delay inactive after defrost.

      In 'merican English that means if it's below 37.5F for longer than 30 seconds while in heating mode, it will run the pan heater 5 minutes after every 25 minutes of compressor operation (which is 10 minutes total per hour.) When entering defrost mode if it's lower than 34F for 10 seconds or more it turns on the pan heater for the remainder of the defrost cycle, and keeps it on for 5 minutes after the defrost cycle ends.

      That's a bit more sophisticated than plugging in your cobbled-on heat tape when you notice an icicle coming out of the pan drain, eh? :-)

      Many other vendors just turn it on and leave it on whenever it's below some outdoor temperature.

  7. jameshowison | | #8

    What are you doing for outside ventilation? I think you'll find that you'll need ducts into your bedrooms just to provide fresh air.

    That argues for a designing in a ceiling service cavity and running ventilation, ducted heating and cooling. Probably you can get away with a four-inch cavity? You have 9ft ceilings, right? Plenty of space :) Something like taped osb as the airbarrier above the cavity, then drywall as the ceiling.

    If I were doing it I'd be pushing hard for having both water and electric in the service cavity as well making remodeling possible without disturbing insulation etc in the attic.

    Keep in mind that the ducted mini-splits need a service space underneath them (18"?), so either they are in the attic space (boo) or in a deeper part of the service cavity (~10?) with a hatch under them (yeah), perhaps above a hallway (they are too wide for access through top of closets, sadly).

  8. dirtriding4life | | #10

    Thank you for the replies everyone. I'm glad to have Dana in the mix. I just read Nate The House Whisperer and am motivated to build this home as efficient as possible within budget on the initial build.

    Yes, the home is in Tumalo which I haven't been able to find a design temp for there so I used Bend since they're 5 miles apart. I've taken the cue that breaking the thermal envelope even with closed cell foam on the ducts is not ideal. I will bring up the idea of some plenum trusses to the builder, but I am afraid it could be too late since framing will be beginning next week.

    That might mean that a ceiling service cavity is the only option. We might be able to fit the unit into the top of the hall closet and run the 4" ducts to the bedrooms from there. Unfortunately it wouldn't be as visually appealing as the plenum truss. Bummer.

    As far as brand selection, I believe the builder is set on using their current HVAC contractor who is a Mitsubishi Diamond dealer. I looked up dealers for Fujitsu and Carrier locally and the options are limited. The quote for Option 1 had the PEAD-A09AA7 with .6in of static pressure and 11.5 HSPF rating.

    I haven't considered the need for outside ventilation. The builder said that the clients (about 10 of them) who have the same floorplan or smaller have been happy with only the wall mounted unit in the great room for heating and cooling. I'm curious if the factory option with some quality ceiling fans in the bedrooms would meet our comfort desires? Electricity is cheap here at less than $.10/ kW so I'm sure it would take a long time to recoup the added cost of the horizontal ducted unit compared to heating with resistance heaters.

  9. jameshowison | | #11

    Ventilation without ducts could be done with the Lunos: There are other similar options too :)

    Perhaps it's because we're pulling wiring for a renovation now that I am pining for a service cavity!

  10. STEPHEN SHEEHY | | #12

    My house is just a bit larger than yours, in a colder, zone 6 (99% design temperature of 0°F) climate. I'd opt for the factory option. A single minisplit should take care of almost all of your heating. Just leave the bedroom doors open during the day. Spend the money you save, by keeping things simple, on a better envelope.

    Over Christmas, our daughter stayed in our guest room. She found that running the resistance heat for a few hours and then shutting it off when she went to bed was more than sufficient to keep her warm, with the door closed. She really hates to be cold, so anyone else would have skipped the resistance heat.

  11. Jon_R | | #13

    Keep in mind that if you keep the bedrooms at the same temperature as the great room, 100% of the bedroom heat load will come from the resistance heater. The heat pump will only supply any bedroom heat when the bedroom is cooler.

  12. dirtriding4life | | #14

    I thought I should get on here and give everyone an update. I decided to go with the standard option of only the single ductless unit in the great room and some quality ceiling fans for the bedrooms.

    Now I am beginning to work a plan to improve air tightness. I am hoping to do a blower door test with a fog machine to find leaks, then seal it myself with foam and tape. The contractor doesn't include the test as standard so I contacted a local energy auditor and they can do a blower door test for $100. I am confused about which stage of the build to schedule this for. The home has a vented attic and crawl space so I would assume my air barrier on the lid will be the drywall, right? Would the only option be to have the test done after the drywall is in but hopefully before attic insulation?

    Please excuse my building experience ignorance. I'm thankful there are forums like this to help.

  13. walta100 | | #15

    The fog machine sounds like a good idea and was very impressive on the This Old house episode I saw.

    I decided not to fog my house, my concern was the fog could contaminate surfaces and cause a problems painting or caulking sticking. Any and all problems would certainly be blamed on the fog weather it is true or not. I felt like it would give a free pass to every sub to blame the fog.

    As for timing the blower door test, I could not find a good point while under construction to do the test. You can’t do the test until the ceiling drywall is in. Are you willing to pay extra to have the ceiling put in week before the walls? If not all you can do is calk and tape the things you can see and test when you are done.


  14. dirtriding4life | | #16

    Thanks for clarifying the ceiling barrier Walta. This is a standard spec home that I’d like to get to “pretty good” levels of air sealing. It might help that it doesn’t have ductwork. I will see what the builder is willing to do of having the ceiling put in before the walls.

    What are people doing instead of recessed lighting? I had plans to do shallow mount LEDs and air seal the trim, but it seems even that is frowned upon. I’d like to have good consistent lighting across the great room and kitchen rather than a couple fixtures with very bright lights to make up the difference.

  15. vashonz | | #17

    I'm not sure about when the right time to do the blower door test, it almost seems best to do it multiple times throughout the build process.

    There is also an aerobarrier dealer in Bend. That may be an option to get pretty good levels of airsealing after drywall and everything is in.

    We're doing surface mounted LED lights installed in J boxes. We're working with Accent lighting in Redmond to figure out the lighting plan, and what lights to use. Our build is a little different that the envelope is completely separate from anywhere ceiling lights are mounted, but still need to keep them relatively shallow.

    What company is doing the door test? Our envelope is basically done, I'd like to see where we are for air sealing.

  16. brad_rh | | #18

    I used standard J boxes and surface mount LED's also. I got up in the attic and sprayed great stuff around all the J boxes, and plumbing and electrical penetrations
    If they do a good job with the air barrier and caulking where needed, and you (or your contractor) take care of the ceiling penetration, you'll have a decent envelop. That's what I did and the blower door test showed 1.5 ACH. Some will have different opinions, but I thought that was good enough. I did the blower door test after the walls and sheetrock were done, but before the attic insulation.
    It's probably too late, but I had it in my contract with the GC that they shall be less than 3.0 ACH (2015 IECC).

  17. dirtriding4life | | #19

    I had not heard of Aerobarrier. I think that will be a great solution for air sealing once the drywall is in. I contacted the dealer in Bend and got some info. They said they can get to around 1ACH50 for what I thought was a reasonable price. I’m planning on using this approach.

    After some more discussions I am realizing that the builder doesn’t prioritize air sealing so the Aerobarrier should be a good way to make up for some of the shortcomings in the envelope. Everything else with the build has been great to my knowledge and they have been super accommodating to my changes and options for a spec home.

    I got some more info on the can lights they traditionally use. They are a relatively shallow LED that has an air seal gasket for the trim. I will probably go back later and caulk them, but I think it will be good enough for what I’m looking for.

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