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Thread: Help with Aprilaire 700

  1. #1
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    Help with Aprilaire 700

    Hello everyone and Happy Thanksgiving! We have an Aprilair 700 whole house humidifier along with a new efficient, variable speed furnace. The furnace works great, but the humidifier does not. It's hook up to our hot water supply. We have a tankless water heater. I just today realized that the humidifier doesn't demand enough water to kick the tankless unit on. So, it's essentially using cold water.

    Would a dedicated water heater (tank) do the trick? If so, how big would I need to go? 2.5 gallon? 4 gallon? 6 gallon? Bigger?

    It seems to me that, if nothing else, hot water would increase humidity performance.

    Thanks for your help!

  2. #2
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    This is something that has never crossed most people's mind when switching to tankless, the low demand items.

    I had a customer with the same issue and he was going to deal with it on his own, so not sure if/what his solution was.

    There is a debate as to the need for hot water to achieve your goal.

    You ned to make sure the tank is large enough to deliver/produce the maximum capability of the humidifier.
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  3. #3
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    Thanks for your response. I think my humidifier uses about 6 gallons per hour at peak use. Does that mean I need a 6 gallon tank? Or would a 2.5 or 4 gallon unit work?

  4. #4
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    I assume you just had the 700 installed? Have you considered just biting the bullet and switching it to an Aprilaire 800? If you get a separate water heater, you’re gonna have to run a new circuit anyway plus make some plumbing modifications. At that point, why not just put a steam humidifier and dramatically increase the capacity with much less waste water?

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  6. #5
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    That's a fair point. I had it installed a little over a year ago. To switch to the Aprilaire 800 would be about $ to $ installed. I doubt I could sell my Aprilaire 700 for even near what I paid for it since it's a year old.

    If I could do it all over again, I'd do the Aprilaire 800. For now, I was hoping to salvage my Aprilaire 700 by running a small water heater. A 2.5 gallon unit would cost about $ + materials. I could probably do all of the work myself.

    Just curious whether I need something bigger than 2.5 gallon. The Aprilaire 700 uses about 6 gallons of water/hour.
    Last edited by beenthere; 11-26-2020 at 08:31 PM.

  7. #6
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    Probably need a 6 gal. with a 6 gal. recovery rate because depending on the size of your house and conditions the humidifier may run over an hour at times, even if this water heater is right next to the humidifier. I really think you’d be far more satisfied with the 800.

  8. #7
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    Thanks CircusEnvy! I'll reevaluate whether I can swing an Aprilaire 800. You're right - might be better to cut my losses.

  9. #8
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    A 2.5 gallon water heater would be find, if your going to set the water temp to 100, and your incoming water temp is 50 or above. Only take 732 watts, to heat 6 gallons of water from 50 to 100 degrees.

    1320 watts, if heating from 50 to 140 degrees.

    Is your 700 mounted on the return or supply duct. How high are you setting the humidistat.
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  10. #9
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    Good to know! My 700 is mounted on my return (hence why I think it's so important to fix the hot water issue). We usually set our humidity to 40% or so.

  11. #10
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    Quote Originally Posted by sb4387 View Post
    Good to know! My 700 is mounted on my return (hence why I think it's so important to fix the hot water issue). We usually set our humidity to 40% or so.
    Yeah, on the return, it doesn't humidify very well. A 600 would have been a better choice.

    Are you using the manual humidistat, or the automatic one.

    On the return, while both 100 and 140 degree water will be a big improvement, 140 degree water will work far better than 100° water will.
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  12. #11
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    Duly noted. I'm not sure I can get to 140, but I can get above 100. I guess anything above 100 (and closer to 140) is better than nothing.

  13. #12
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    Quote Originally Posted by sb4387 View Post
    Duly noted. I'm not sure I can get to 140, but I can get above 100. I guess anything above 100 (and closer to 140) is better than nothing.
    Most electric water heaters can go to 140. And since its for the humidifier only, no worry about scalding.
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  14. #13
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    Noted. Thanks for your help!

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