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Community and Q&A

Panasonic WhisperValue DC fan and TRB transfer box – anyone using these in the field yet?

Nick Welch | Posted in Mechanicals on

For a while now I’ve been considering different ideas to distribute the air from my mini split to bedrooms when the doors are closed. I just noticed that Panasonic recently came out with a new DC motor version of their 3 3/8″ deep WhisperValue fan, with selectable speeds (50/80/100CFM) and pretty low sone (noise) ratings.

They also make this transfer box that’s designed to fit this fan (google Panasonic TRB — I can’t link anything or the spam filter gets me).

This creates a setup that fits into an existing 2×4″ framed wall and blows air from one side to the other. I could put it above each bedroom door and it’d pull air from the hallway (which the mini split blows down). Each bedroom already has an obsolete 6×12 register that leads down an abandoned duct to the basement — this could now act as the “return”. It seems like an ideal solution. Better than the Tjernlund AireShare (which is louder and pushes fewer CFM). And better than putting exhaust fans in the hallway ceiling and losing 8″ of headspace. But this is all fairly new stuff and I haven’t seen any first hand accounts of how well it works in practice. So — have any of use used this setup yet? How’s it going?

I have one question in particular: The output of the transfer box is sized for a 4″x10″ register. At 50, 80, or 100CFM, how far would the air noticeably “throw”? Would care need to be taken to direct the air at the ceiling, or away from people, to prevent a drafty feeling in the winter? (Given that it’s blowing nearly room temperature air)

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  1. Anon3 | | #1

    If you got duct work you can use a single inline fan and run the duct in reverse (pull from all the rooms and dump out the supply)

    Eg: the fantech FG EC series, no need to rip out the walls and could actually deliver CFMs efficiently.

    You'll need more than 100CFM each room to make a difference. eg: 100*1.08 *5f diffference = only 540 btu

  2. Steve Knapp CZ 3A Georgia | | #2

    I believe Carl Seville used this strategy on his recent build ( He might be able to offer some advice.

  3. GBA Editor
    Martin Holladay | | #3

    Interest in this type of experiment waxes and wanes here at GBA. But every experimenter comes up against the same hard fact -- namely, that air has a specific heat of 0.0182 Btu/cf/°F.

    If it the cooling season, you'll find that it's hard to lower the temperature of a bedroom that is at 79°F if you are delivering hallway air that has a temperature of 73°F.

    Similarly, in the heating season, you'll find that it's hard to raise the temperature of a bedroom that is at 66°F if you are delivering hallway air that has a temperature of 73°F.

    One hundred cfm won't do it. One hundred cfm is needed when you are delivering air from your furnace plenum -- but you're delivering hallway air.

  4. Nick Welch | | #4

    Yeah, I get it -- I don't expect to keep the bedrooms the exact same temperature as the rest of the house. But it was 100F here last week and my baby's head was laying in a giant wet spot on his bed, two days in a row. Surely the needle can be moved. Cutting the temperature difference roughly in half for ~$10/yr of energy would be worthwhile, I think. Humidity and smell would benefit as well (we have 3 boys...). Closing the doors at nighttime is sometimes mandatory for sound reasons.

    As for inline fans... even the most efficient seem to use 2 or 3 times as many watts per CFM as the best bathroom exhaust fans. The Panasonic fan I mentioned moves 9.2 to 12.8 CFM per watt, depending on speed. The Fantech ECM 4" inline model that moves 150CFM gets 5.4CFM per watt. Maybe I'm splitting hairs but that just bugs me.

  5. Expert Member
    Dana Dorsett | | #5

    It's easy to manage the latent loads (humidity) of remote rooms by moving air with small fans, even 20 cfm is enough, but not the sensible loads (temperature). Assuming you even get the full 150 cfm that's still only 810 BTU/hr @ 5F delta. Even 250 cfm at a 5F temperature difference is only 1350 BTU/hr.

    A 5 cfm fan blowing gently on the crib to keep evaporating the baby-sweat would keep the baby cooler & more comfortable, and the pool of sweat soaked bedding would not occur.

  6. Jon R | | #6

    At some point, one might put comfort before economy and get a Chiltrix chiller with hydronic fan coils.

  7. Nick Welch | | #7

    I'm revisiting the simulation I made for this a while back... (well, I can't link it, because I get spam-filtered) and I just can't make the numbers work. The 100CFM fan indeed makes such little difference. It doesn't even cut the delta in half. It cuts like 20% of it. Perhaps it makes more sense in a superinsulated house, but my house is just regular-insulated. I guess I should steer my obsessive tendencies elsewhere. I can't change the laws of physics.

  8. Anon3 | | #8

    Since you got the duct, why hook up an AC to it? Also, inline fan is a lot more efficient than the Panasonic fans, the one I linked you can do 23.28 CFM per watt at 204 CFM .1 inch for example

  9. Nick Welch | | #9

    I assume you meant, "why not hook up an AC to it"? Because a ducted mini split system would have been significantly more expensive, and less efficient. The bedroom problem is not a huge deal, but I like to try and solve problems even when they're not big. (Though I may have to admit defeat on this one -- which is okay)

    That 12" Fantech fan says 807CFM and 166W. 807/166=4.86CFM per watt. Am I missing something?

  10. Anon3 | | #10

    Go to the diagram section on that page and you can find power usage at different speed and static pressure.

    Also, check out the ducted units at say acwholesalers, there's a couple $1000 units there, just get an AC tech to commission it for under $500.

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