Switching from Panasonic wall heat pump to integrated central heating and ventilation

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Greekiwi

55 posts

Master Geek

#318940 7-Mar-2025 09:48

We bought an off the plans house that was completed last year. The plans provided for two wall mounted Panasonic heat pumps:

One in the open plan living room/kitchen down stairs
One on the top floor, directly over the stairs (see plan below)

While it was being built, we had a trusted friend recommend putting in a ventilation system. We opted for a Mitsubishi Lossnay system.

We have no issues with the downstairs heat pump. However, the upstairs heatpump is really inefficient for heating or cooling anything except the bedroom whose door it directly faces. We are thinking about switching the upstairs to a ducted central heating solution with zone control for the three bedrooms.

My question is, if we switched to Mitsubishi ducted heating upstairs, could we make use of the ventilation system to avoid two sets of ducting?

The floor plan for the upstairs is below. The three green dots in the bedrooms are the outlets for the ventilation. The green dot in the wardrobe is the duct dropper for the ventilation to the living room down stairs. RA is the return air slot for the ventilation.

timmmay

20574 posts

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#3350894 7-Mar-2025 10:11

Hallway heat pumps don't tend to work great to condition the air in bedrooms.

The ventilation system ducts don't look well located for HVAC. Generally you would want them on the opposite side of the room from the return vent, as ducted systems let air drift across a room rather than blow it around. You can get around that somewhat by using MDO diffusers that direct the air, but relocating the diffusers would be better. Once that's done you can use the same diffusers for both, if you integrate the lossnay with the HVAC.

There are a few good threads on ducted systems. This is one, and there's an FAQ I wrote.

Updated - You should also consider high wall heat pumps in each room - I suggest Daikin rather than Panasonic if you go that way. They're simpler, no need to worry about returns, the person in the room can easily set their own temperature, and with a multi-split they can run off one outdoor unit. My wife doesn't like the ducted unit much, I like it fine but it takes WAY more effort to manage than a standard heat pump. I've spent a huge amount of time on home assistant automations to make it work how we want, changing when it starts and stop based on temperature, month, directly changing dampers sometimes, that sort of thing. However, with a ducted system and a bypass damper a lot of that isn't needed.

Greekiwi

55 posts

Master Geek

#3351005 7-Mar-2025 14:12

Thanks that's really helpful information!

I am looking to get started in the world of Home Assistant so I am theoretically not opposed to that. With a bypass damper, would you need one for every room for that to be effective?

timmmay

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#3351018 7-Mar-2025 14:38

Have a read of my FAQ. You need one bypass damper for the whole system, it adds about $500 to the price of the system but eliminates spill which is a huge benefit. It massively reduces the amount of work you need to do in HA to tweak it. Don't discount the multi-split unit, it also eliminates the need for undercut doors or wall vents.

GV27

5896 posts

Uber Geek

#3351022 7-Mar-2025 15:04

We got an uprated multi-split external unit to power our existing Panasonic heat-pump and added one to 2x kids bedrooms upstairs, happy with the outcome. We over-rated it to make sure we had capacity to add one in the final bedroom if we decided to go down that route. We went the basic spec option for wall units for size and cost reasons, but it also sounds like we've been lucky as some experiences with the Panosonic pumps seem to vary pretty wildly. I was not enthused by the security on the wireless modules for the Panasonic units and given they can cool the rooms down in less than ten minutes, we decided not to bother.

We also have a Smart Vent positive pressure system and the two seem to play nicely together. It was too costly to go with a ducted system feeding through the existing vents and we couldn't be sure either would do their job properly once we did it. I'd consider it with a new build but i didn't want a second set of holes in the roof either.

Unfortunately the remotes for each wall unit are identical so I foresee issues when the kids are old enough to muck around with each other's heat pumps.