Just found this thread addressing the use of Panasonic's Whisper Green with a ductless heat pump.  No distribution system other than the Whisper Green moving air between rooms.


Curious about your thoughts. 

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The concept of using a ceiling-insert ERV next to a ceiling-insert ducted DHP appears to work well to distribute the tempered air being discharged by the ERV.  This provides good distribution to all heated/cooled rooms because it is using the ducted DHP and its ducts to distribute the tempered and conditioned air.  As we build/retrofit houses to be much tighter and to use much less energy, a DHP can provide most or all of the heating required.  In the Pacific Northwest, a demo retrofit program has installed over 7,000 DHPs in existing electrically heated homes throughout the four Northwest states, mostly with single head wall-mounted indoor unit systems.  As mentioned in the earlier postings, one approach to distribution that has been tried is to use a single ceiling-mounted fan to provide distribution to bedrooms.  While this works fairly well, it is limited by the heat capacity of the air being moved to be able to overcome the heat loss in the bedrooms.  It will not work well in a high heat loss situation.  The advantage of the Panasonic DC fans is that they will maintain constant airflow over a variety of static pressures.  So when they are used for distribution, the fan will speed up to maintain the airflow that has been set at the fan whether the door is closed or open.  Distribution always works better when there is a return path for the air being discharged into the room.

By ductless heat pump are you refereing to a mini-split air conditioner/heat pump?

Yes - for more information (webinar audio and presentation, and access to resources) on ductless heat pumps, go to:

The Pacific North West ductless heat pump field monitoring results were limited to single-zone (one outside unit one inside unit) ductless systems.


Minisplits are not necesarily ductless.  Some minisplits may have a small ducted system.  Dave Robinson,  buys foreclosed homes in central California that he renovates, using two,1 ton Fujitsu minisplits. He ducts one to the bedooms and bath with very limited ductwork  located in the hall celing.  The other unit is ductless, and conditions the living room and kitchen of the one-story ranch homes.  There are significant cooling loads with lots of 100 degree weather.  His approach of combining ducts and ductless results in simple systems and homes with low energy bills.   Dave has case studies posted on his website.


To be more exact, we use one outside unit (2 ton is the smallest they make in this model - so we use it on everything)    One inside unit is the conventional mini split high on the side wall in the main room ... the one that everyone associates with mini splits.    The other inside unit is mounted on the ceiling at the mouth of the hallway & delivers air to all the rest of the rooms thru a small duct system that we mount on the existing ceiling of the hallway.   So the unit and all the ducts are inside the envelope.  Then new drywall is added, reducing the hallway height about 10 inches.   We throw the factory filter away and allow a 20 x 30 filter grille right under the air handler provide a lot more filter area as well as access to the unit without breaking the building envelope.    You can see pics of this hybrid duct design at A Good Business? How Long? Plus Ducted MiniSplit Update   (Click the right arrow on the photo in the center of the page and it will take you thru a few other slides from that webinar and you'll get to the Mini Split photos) You'll notice we use galvanized pipe.   That, along with the oversized return keeps the static way down.  which is essential for efficiency on these units.    This unit has now been in two years.   The owner loves it.  Zero problems.    Has utility bills less than half of his neighbors.   Here are 12 months of bills ... straight from the utility.   which is PG&E , one of the most expensive kilowatts you can buy in this country.








Bill Date

Electric Usage (kWh)

Electric Charges ($)

Gas Usage (Therms)

Gas Charges ($)

Total Charges ($)

Feb 4, 2011






Jan 5, 2011






Dec 7, 2010






Nov 4, 2010






Oct 6, 2010






Sep 5, 2010






Aug 5, 2010






Jul 7, 2010






Jun 6, 2010






May 6, 2010






Apr 7, 2010






Mar 7, 2010






Feb 4, 2010







 As Linda mentioned above, this house is in Fresno and those summer bills are pretty low.

This job also used a Panasonic ERV instead of the exhaust only scheme that you are considering.   We mount the ERV very close to the return of the ducted system and in the pick-up area of the wall mounted unit so all fresh air is circulated by the main system with no additional equipment needed.  It works well for us and we have adopted this as our main system.   It's the one we specify every time unless we are keeping old equipment that's not too old or too over sized for after our renovation.   You'll also notice that we mount the outside unit on the roof instead of on the ground.  Lots of reasons.   



How do we know how much energy is used with the Panasonic DC fans? Or how much airflow will there be with given duct configurations? Well, attached is a fun summary of some quick research conducted to help answer these questions. These fans are a pretty bulletproof and can survive crazy, real world installation configurations.

Enjoy. Bruce Manclark, Ben Hannas, Jonathan Coulter


Practical recommendation requested.  What is the best way to move heat from 2nd floor to 1st floor?

Don and others - -

I have a situation where I would like to add a Panasonic Whisper Green fan to increase a home's ability to benefit from the use of its upstairs ductless heat pump (DHP) for heating. This unit clearly has unused heating capacity, as its heating energy use last year was only 402 kWh.


Anything better than Panasonic Whisper Green DC variable speed fan?

What sized fan would be best?

Where to locate the fan?

How should fan be controlled?


Attached is a presentation that includes data from this house - It is the Western PA Farmhouse on slides 22 to 25. Energy improvements are being done over time. At this point the upstairs walls and attic are well insulated; downstairs is only partially insulated. Upstairs does not need additional heat, so the RLS 9 Fujitsu DHP (9,000 Btu) ran little last winter compared to downstairs DHP. It was installed upstairs in a large bedroom, with the primary intention of providing air conditioning. There is a RLS 15 Fujitsu DHP downstairs that was used to offset as much heating as possible. The propane furnace was used when they needed to raise the temperature quickly and when the DHP could not carry the load.

Both DHPs are submetered. They saved a significant amount of propane (~350 gallons) Note: winter 2011-12 was warmer than winter 2010-11, and the propane dryer was also disconnected during the winter; this reduction is not weather adjusted, or specific to just the offset in heating. Hopefully over the next year or two the rest of the home with be insulated and air sealed. That is going to happen for this winter. For heating the total DHP use was 2,072 kWh, the downstairs DHP used 1670 kWh and the upstairs one used 402 kWh. For AC, the DHP energy use was 1,000 kWh, 553 kWh upstairs and 482 kWh downstairs).

It should be possible to offset more propane heating if we could use the upstairs DHP to help heat the downstairs. Doing so is certainly less expensive than adding an additional DHP downstairs (~$3,000). In addition, the 3rd DHP should not be needed once the house is insulated and air sealed. We want to create air movement to the room directly under the upstairs bedroom with the DHP.

Is it more effective to install a fan at the ceiling of the bedroom and blow the air down to the floor of the room below through a duct - or to blow colder air from the room below to the room above? There are transoms over the doors so there is a pathway for circulation even when doors are closed. The home's central forced air system  that was installed 50 years ago appears to have been properly sized for a higher cooling/heating load, so there are (2) dedicated 4 x 16" ducts serving each room. It doesn't appear to be a problem to disconnect and re-use some of this ductwork to achieve the desired airflow between these two rooms. The question is where to locate the fan so that it will be most effective. We are not trying to zone heat the room below, just move heat to the first floor and not overheat the bedroom.

Not that it matters, but the farmhouse has big rooms (17.5 x 17.5 sq. ft) and 9 ft ceilings. The bedroom is right off of the home's main staircase, which is centrally located. There is plenty of opportunity for air flow within the home, and between rooms on each floor. Obviously, tightening and insulating the home is a priority, and has the potential for a significant impact on comfort. At this point, affordability is the highest priority, comfort is secondary, as the occupants are tolerating a lower level of thermal comfort than most people would consider acceptable.

I welcome questions and suggestions!


This slide deck has a little more info - slides 22-26 address the Western Pa Farmhouse referenced in my  reply immediately above


Also info not in the thread above, but here on the use of Panasonic fans for disribution with DHPs.


I've got no great solutions Linda.  I've seen some people use in-line fans with variable-speed controls, but these tend to use quite a bit more electricity.

If this is really a temporary issue -- and more work will be done soon to reduce the loads downstairs -- is it worth putting a lot of effort into an air mixing system?  Could you use the existing furnace fan to mix air?  Maybe add a BPM motor (Concept3 or Evergreen) if you're concerned about AHU energy? (though those aren't cheap...)

As for where to suck/blow, I'd say suck the warmest air (where practical) and blow it to the cooler room.

Thanks Robb -

While getting the extra heat from the second floor to the first floor won't be as important once the home is fully insulated and significantly tighter, there will still be the benefit when it is really cold, and when they want to heat up the downstairs more quickly.  Both of those applications will reduce the need for propane in the future. I am assuming that this effort (getting 2nd floor DHP heat to the 1st floor) will have value in both the short and long-term.

Definitely low operating energy use is a high priority, also first cost.  That is why the Panasonic DC fan is ideal.  The mental framework for this project is achieving deep reductions - AKA Thousand Home Challenge, so every investment is made from that context.  

They did try using the central air handler for mixing air both winter and summer - as I recall, it did not have a huge impact. The furnace fan probably uses as much energy (or more) than the DHP. We could experiment more by setting the upstairs DHP on 80 for a while. However, the sheet metal ductwork in the basement is not insulated...

I think we have a good way to pull air off of the ceiling on the second floor near the DHP by taking over one of the existing supply ducts. It may be tricky to avoid discomfort blowing it into the room below, as it will probably be 70 - 75 degree F air. Is it best for mixing & comfort if we locate the register high in the downstairs room, or better to get it as low as possible?




We did an evaluation of some very low-load homes in western MA using a single gas unit heater in each home, exhaust-only ventilation, and a WhisperGreen fan to equalize temperatures and outside air.  Seemed to work very well, but the very low loads are critical.  A link to a report on this project is below; we're interested in investigating this further!



I would suggest using the 130 cfm DC fan, the Panasonic FV-13VKS3, mounted in the insulated ceiling or in a thick wall (2x8 depth needed) pointed down so that the 6 inch discharge could be connected to one of your existing 4x16 vertical duct risers.  As you say, it is important to remember that the temperature will be warmer than the room below but will still be chilly if it strikes the homeowner. So use an air conditioning grille with some throw to spread the air out across the downstairs ceiling.  The 13VKS3 gives you the ability to set the airflow at 50, 70, 90, or 110 cfm with a boost to 130 cfm when the control switch is thrown so the homeowner can do a bit of adjustment based on comfort and effectiveness.



Don -

Are the fan flow settings (50 to 110 cfm) for the FV-13VKS3 behind the grill? 

Mounting the fan to get the discharge into the top of the 4x16 vertical riser should work, though it will take some ingenuity.  Can the fan be turned so the grill is vertical and the discharge facing down?  The duct is in a closet and there is a dropped ceiling directly above it. That space should be big enough to mount the fan with the grill cut into the top of wall, assuming it is OK to mount the fan that way.



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