Panasonic vs Mitsubishi ducted heat pump and ventilation solutions

Forums › Home Workshop DIY › Panasonic vs Mitsubishi ducted heat pump and ventilation solutions

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Kickinbac

487 posts

Ultimate Geek
+1 received by user: 104

#3482088 19-Apr-2026 13:21

AlDrag:

I just found out my return plenum is installed like this! Oversized, so they just forced it on with tape lol. I posted it on "My Efficient Electric Home" Facebook page, and everyone is having a laugh...standards must be higher in Aussie or I just got bad luck haha. They're even laughing about the wire mounting.

I always make an internally insulated return plenum at least 400mm long. This allows the air to equalise over the coil.
I do a special detail for these Mitsubishi ducted units as they are awkward to connect a plenum to as it has a turn in on the back, not a raw edge spigot. I get a 30mm spigot made to attach to the unit first then have the return plenum to fix onto that. Either a mez flange or slip over connection as our return plenums have either 25 or 50mm internal insulation so there is a step in the sheetmetal. Lots of duct sealant. Any bare metal is externally insulated with ductwrap as it can condense water here and drip, particularly in a hot humid Auckland summer!

I’m sorry you’re in this situation. My company mainly does commercial work as it’s a fight to the bottom in residential in both price and quality. The crap installation we see is sometimes unbelievable then you hear what they paid and they saved about a thousand dollars.

AlDrag

284 posts

Ultimate Geek
+1 received by user: 29

#3482535 20-Apr-2026 14:18

tweake:

@AlDrag this might be interesting https://youtu.be/prllbzLfmaA?si=BCc0o6OZZVleuHoY

It was an interesting video, but I don't think too relevant in my case? I have static pressure only _slightly_ higher than factory (70pa instead of 50pa).
I was using the highest settings previously and it wasn't as cold and was just too much airflow. I suspect this is because the air doesn't spend as much time on the coils, especially with my shitty return plenum.

AlDrag

284 posts

Ultimate Geek
+1 received by user: 29

#3482538 20-Apr-2026 14:23

Kickinbac:

I always make an internally insulated return plenum at least 400mm long. This allows the air to equalise over the coil.
I do a special detail for these Mitsubishi ducted units as they are awkward to connect a plenum to as it has a turn in on the back, not a raw edge spigot. I get a 30mm spigot made to attach to the unit first then have the return plenum to fix onto that. Either a mez flange or slip over connection as our return plenums have either 25 or 50mm internal insulation so there is a step in the sheetmetal. Lots of duct sealant. Any bare metal is externally insulated with ductwrap as it can condense water here and drip, particularly in a hot humid Auckland summer!

I’m sorry you’re in this situation. My company mainly does commercial work as it’s a fight to the bottom in residential in both price and quality. The crap installation we see is sometimes unbelievable then you hear what they paid and they saved about a thousand dollars.

Sounds complicated to install/make. What would it cost to get something like that made roughly? I don't think my return plenum has any insulation in it, but I will find out when I eventually pull it apart (or just pull off a duct).

Thank you. I didn't even look for the lowest price. Only got a few quotes and they were all basically the same. I just picked these guys due to the excellent reviews and the boss is really nice. I just wish they would talk to me about compromises before installing shit like this, I could have talked about forsaking lossnay or something to do a cleaner install.

tweake

2717 posts

Uber Geek
+1 received by user: 1169

#3482542 20-Apr-2026 14:28

AlDrag:

It was an interesting video, but I don't think too relevant in my case? I have static pressure only _slightly_ higher than factory (70pa instead of 50pa).
I was using the highest settings previously and it wasn't as cold and was just too much airflow. I suspect this is because the air doesn't spend as much time on the coils, especially with my shitty return plenum.

just how the plunum is done and air flow rates.

the faster the airflow the less the difference between inlet and outlet temps, but it does more passes. the less difference the less dehumidification but generally more efficient. changing the temp a little bit each pass, but doing more passes. the downside is the sizes of ducts, duct leakage and any outside air being sucked in on the return. higher speeds makes that worse.

Kickinbac

487 posts

Ultimate Geek
+1 received by user: 104

#3482553 20-Apr-2026 15:05

AlDrag:

Kickinbac:

I always make an internally insulated return plenum at least 400mm long. This allows the air to equalise over the coil.
I do a special detail for these Mitsubishi ducted units as they are awkward to connect a plenum to as it has a turn in on the back, not a raw edge spigot. I get a 30mm spigot made to attach to the unit first then have the return plenum to fix onto that. Either a mez flange or slip over connection as our return plenums have either 25 or 50mm internal insulation so there is a step in the sheetmetal. Lots of duct sealant. Any bare metal is externally insulated with ductwrap as it can condense water here and drip, particularly in a hot humid Auckland summer!

I’m sorry you’re in this situation. My company mainly does commercial work as it’s a fight to the bottom in residential in both price and quality. The crap installation we see is sometimes unbelievable then you hear what they paid and they saved about a thousand dollars.

Sounds complicated to install/make. What would it cost to get something like that made roughly? I don't think my return plenum has any insulation in it, but I will find out when I eventually pull it apart (or just pull off a duct).

Thank you. I didn't even look for the lowest price. Only got a few quotes and they were all basically the same. I just picked these guys due to the excellent reviews and the boss is really nice. I just wish they would talk to me about compromises before installing shit like this, I could have talked about forsaking lossnay or something to do a cleaner install.

This is how I draw them, this detail was for a commercial building. Cost around $400-500 +GST. Any Sheetmetal shop that specializes in HVAC duct can make them.

There are options from the suppliers, like Daikin, for residential ductwork kits that come with the plenums, flexi and grilles that are specifically sized to suit a specific ducted indoor unit. For the plenums, they use a foam board called P3 duct. The insulation board has aluminum foil on both sides, its very lightweight.

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