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Big honking supplemental dehumidifiers

My buddy Blake Reid just posted this. Well worth a read. It's short.


For those of us in green grass climates, I'm becoming a bigger and bigger fan of these things. We recommend them for EVERY project. That doesn't mean they get installed. I particularly like ventilating dehumidifiers because they bring in outside air and pressurize a house a touch, which can tend to push contaminants outdoors. They also tackle dehumidification when there isn't cooling load, which is about 6 months/year here in Cleveland. They can allow much higher AC set points, pushing 80 degrees.

Blake has an XT155 in his basement. I just bought one too, I'll install it in the next few weeks. Four of my clients have them. Supplemental dehumidification was a subject at Summer Camp. (Ken Gehring of Thermastor spoke there this year, and was kind enough to donate a little dehu for the Habitat project we helped with.)

I'm coming out hard for these things. If you aren't recommending them for projects and moisture is an issue in your climate, you might consider it. That way, if there is a moisture problem later and the client doesn't do it, you're covered. Thoughts?


  • Nate AdamsNate Adams Posts: 565
    Also, while I will fight almost to the death to downsize HVAC systems, I see little downside to oversizing dehus. (They do add a substantial amount of sensible load, but there are split models that eject the heat.) In the case of the UltraAire line, once you step up to the XT line, the 105 and 155 models come in the same cabinet and only have a few hundred dollar price difference. Hence the big honking one Blake and I bought.

    Props to Blake, he's had it for a few years and does the same thing I plan to do: he uses window units for AC.
  • nperneynperney Posts: 7
    What the trade off in the load calc for not increasing the latent load via lower moisture in the in coming ventilation air stream. I never get to play with humid air, so I'm not sure. You might want to look at pushing that oversize factor of AC's down to just over 90% get some long run cycles with some sweet drying. It might feel a little warm on really hot days, but dry.
  • touchd77touchd77 Posts: 1
    Have you guys calculated the electric use to run these units? Are they energy efficient units?
  • These units are about 4 times more efficient than the little plug in ones from Wal-mart. did you know that even the Energy Star units have the same compressor efficiency? They only improve the fan efficiency. Small potatoes.
    They are great products, and are an excellent choice for many existing homes.
    I have been pretty happy with the Carrier Infinity/Bryant Evolution series of heat pumps and air conditioners; which can run very low to dehumidify without much cooling; at similar efficiencies to the Sante Fe and Ultra-Aire models.
  • Nate AdamsNate Adams Posts: 565
    Yep, Jake, I love the Carrier Infinity equipment too. The trouble is obviously when there is latent load, but no sensible, which is about 8-10 months/year here. For my northern climate, I actually like that they add a little sensible to the house. Just enough heat for those 55 degree days without firing the furnace or heat pump. =)

    I didn't know the Energy Star was just fan efficiency, great info!

    @touchd77 I don't need calculations, I measured. The 70H model uses 600 watts with fan. The XT155 uses just over 800 watts. The XT series seems to be worth spending the money on since dehus use so much energy. Since the XT155 is only a couple hundred more than the XT105, I lean towards getting the big one, which is what several of my clients and myself have done.
  • BryankingBryanking Posts: 1
    Working with crawlspace encapsulation, and firsthand witnessing the mold issues that can develop without insulation, we ALWAYS recommend a dehumidifier for crawlspaces or attics. The Sante Fe dehumidifiers are nicely compact and are offered in a number of different styles and sizes. Very informative post!
  • David ButlerDavid Butler Posts: 3,838

    We recommend them for EVERY project.

    I always push clients toward source control, if at all possible, to avoid the not insignificant energy costs associated with running a dehumidifier. By source control, I'm referring to tight envelop, ERV ventilation in humid climates, appropriate use of spot ventilation, blacklisting commercial range hoods, proper roof drainage, site design, etc.

    In closed crawlspaces, especially in new construction, despite what the code requires, you can avoid DH via source control. If you make the crawl virtually air tight so as to minimize the amount of water vapor that can enter. Ditto with encapsulated attics.

    In new construction, I consider dehumidification equipment to be an expensive band-aid -- expensive up front and even more expensive to operate over the life of the building.

    All of that being said, in retrofit situations, good source control is often cost prohibitive compared to supplemental DH. So I don't have a problem specifying DH systems in such cases, although retrofit rarely comes up in my work.
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