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

correcting new construction install of HRV and dehumidifier

Martin_S | Posted in General Questions on


We recently bought a new construction home in zone 7. In addition to the standard HRV the builder provided, Fantech flex 100H, we had them install a whole-house dehumidifier, Santa-Fe Ultra120.

Our goal was to manage humidity in the summer, late-summer/fall especially when it is humid outside but not hot enough for the air conditioning to run. We told the builder that we wanted to dehumidify the outside air before it came into the house to achieve our goal.

We are seeing the system not reach the programmed humidity level of 45%. The house currently is at 48% humidity. It is cool outside so the air conditioning is rarely running. The outside air is also more humid (60%) than the inside air. It looks like the system is not working to get to the set humidity level.

We have been looking over the configuration and are not seeing how the dehumidifier is being effective as it is ducted. We are wondering how this can be corrected to effectively manage humidity?  Pictures are attached.

Currently the HRV appears to have its own set of ducts independent of the other systems.  The exception being the fresh air output duct may go into the HVAC air handler supply (it’s above the ceiling so hard to see). The Santa-Fe has an intake duct coming from inside the house somewhere and the output from the Santa-Fe goes into the HVAC air handler supply. See photos. The right duct into the Santa-Fe is the intake.

So it would seem in the current configuration that the HRV would run independently on its air exchange cycle bringing in that more humid air. But we are not seeing any active dehumidification taking place (the fan is not running on the HVAC on its own).  The dehumidifier has run at some point as there is a little water in the drain hose. Can this be corrected?

Thank you in advance for your advice!

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.


  1. Expert Member
    DCcontrarian | | #1

    The measure of whether the outside air is more humid than the inside air is not the relative humidity, it's the dew point of each. Outside air at 60% could be less humid than inside air at 48% if the outside temperature is lower.

    That said, I think your question boils down to "why isn't the dehumidifier running if it's 48%RH and the setpoint is 45%?" The answer is probably that there is a bit of an interval set into the humidistat so it doesn't constantly turn on and off. It could turn off at 45 and not turn back on again until it hits 50.

    Where are you measuring humidity? There can be quite a bit of variation within the house.

  2. Martin_S | | #2

    Thanks for the reply. I can see how there could be an interval. We'll find out about that.

    We are measuring it in a few places. The furnace control likely has a humidistat inside the control panel (not completely sure) and that is on the upper floor in a central hallway to the bedrooms and bathroom. The hallway is open to the main living/kitchen area which is a half-flight of stairs down. In the unfinished walk out basement we have a little hygrometer that reads within a few % of the thermostat, usually a little lower. Right now the house is 45%, the basement 42% and outside 53%

    With how the different components are connected, should the HRV fresh air output be connected to the dehumifier fresh air input?

  3. Expert Member
    DCcontrarian | | #3

    It looks like it's working. I don't see what needs to be corrected.

    Of course humidity along isn't enough to tell. What are the indoor and outdoor temperatures?

    1. Martin_S | | #6

      I'm using a dew point calculator and see that I've managed to get the humidity down, but only by running the furnace on recirculate, because the Santa Fe is attached to the furnace. Just wrote this below, but isn't this inefficient? It's more costly to run a furnace than an HRV, is it not, and now I'm running both the HRV and the furnace so we can get fresh air and have dehumidification? They also seem to be working at cross purposes if air is coming in from the HRV and then filtered post-entry by the dehumidifier. My wife is unsurprisingly reactive to a lot of environmental toxins and the fires are getting to her. With the higher MERV rating on the Santa Fe than the fantech, it seems the best idea would be to have the dehu directly hooked up to the HRV, which only has a MERV rating of 8.

  4. user-5946022 | | #4

    Not sure what is controlling your dehumidifier, but as noted above, there is usually a minimum 4% range - for example, if you set the dehumidifier at 52%, it goes on at 52% and runs until it gets to 48% before it goes off (52% is your max humidity). The SantaFe branded dehumidistats have an internal 4% range and work like that.

    Others might work such that if you set it to 52%, it goes on at 56% and runs until it gets to 52%. (The control thinks 52% is your min humidity). This is more common in multifunction thermostats that have humidity controls that can be used for either humidifiers or dehumidifiers. I think there might be programming settings you can do to change if your setting is a min or max.

    Another reason your measurements don't match can be because consumer grade humidity sensors are notoriously inaccurate. I had to bring my Santa Fe controls down 10% from out of the box. I had 5 other humidity sensor, which I tested using the wetted salt method (google it). 4 of the 5 ended up between 74 and 75%. So I presume those 4 work at a higher humidity. All 4 of those measured the humidity in a space that I'm trying to control at between 59 and 62, but the differential among them did nor correlate to the differential observed in the salt test (ie unit 1 was NOT consistently 2% higher than unit 2). But since they were within 3% that was good enough for me. Interestingly, the remote for the wired Santa Fe dehumidistat measured 51 in that same space. I decided that was not correct, and reprogrammed it to have a 10% offset (61%) to match the others....

    1. Martin_S | | #5

      It seems like the dehumidifier is being controlled by the furnace fan. It wasn't doing much until I turned the furnace on recirculate. Shouldn't the dehumidifier be attached to the HRV as well and not only the furnace. First, because the MERV rating is higher on the Santa Fe than on the HRV. So it seems the air (and we've got wildfire smoke she's reacting to) is coming in from the HRV and incompletely being filtered post-entry by the dehumidifier. But it also seems like running the dehu on the furnace is going to be costly if the furnace has to be on all the time.

      Your Santa Fe must be fancier--we don't have a remote. Interested in the salt test--will google, thanks!

  5. Expert Member
    DCcontrarian | | #7

    You could attach an external humidistat to the fan switch on the HVAC so that when the humidity exceeds the setpoint the fan turns on. That way the fan only runs when it's needed.

    Installation is super simple, just replace your existing thermostat with a humidistat thermostat. Connect the fan wire to the dehumidifier output.

    The Garrison 661237 has been my go-to but it seems like it's getting harder to find.

    1. Martin_S | | #8

      Yeah, we know that would be possible. But key here is fresh air all the time for my wife. There is a humidistat in the Honeywell Home thermostat (it tells us indoor and outdoor humidity) and it has controls for the fan, furnace, HRV. We can set the HRV to bring in fresh air continuously.

      A key missing link here for us is the air pathways. Currently fresh air from HRV goes right into the HVAC air handler, bypassing the dehumidifier. So the humid outside air goes right into the house. Then the house air is nominally captured by the intake duct to the Santa Fe somewhere in the house. The Santa Fe has an optional fresh air connection (not currently used) which is seeming like where the HRV fresh air should be routed to properly manage incoming humidity.

      1. Expert Member
        DCcontrarian | | #9

        It really doesn't matter if the humidity is removed before the air enters the house or after it's circulated.

        1. Martin_S | | #10

          It matters for the reasons previously stated.

          1. Expert Member
            DCcontrarian | | #11

            Hey, it's your house, it should be the way you want.

            But I don't see why you're bothering to ask for advice. You came here with the assumption that it was installed improperly, even though you haven't presented any evidence that it's not working. It's just not hooked up the way you think it should be hooked up.

            OK, hook it up the way you think it should be hooked up.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |