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574 posts

Ultimate Geek
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Topic # 231972 23-Mar-2018 12:14
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The talk of late about ducted heat pumps got me thinking. 


Should we wrap the ducting in insulation (as I believe it is just that thin circular stuff with silver (metal reflective??) finish)


If so what should I be looking for when considering the best insulation for the situation (in my case, in the roof cavity). 



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14123 posts

Uber Geek
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  Reply # 1982027 23-Mar-2018 12:28
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I believe there is insulated ducting which they should be using. 


1834 posts

Uber Geek
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  Reply # 1982031 23-Mar-2018 12:30
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We've got insulated ducting for our gas fired heating. 

574 posts

Ultimate Geek
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  Reply # 1982033 23-Mar-2018 12:31
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So assuming there is some basic level of insulation, is there any benefit with wrapping it in any more? (I am thinking it is probably just standard cheap stuff) assumptions and all :\

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Uber Geek
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  Reply # 1982040 23-Mar-2018 12:48
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Is this for an existing or new system? If the latter, can you not just specify a higher-rated ducting?

But, yeah, the ducting in our heatpump central heating system is def. insulated, but I understand there’s a decent loss and is one of the reasons ducted systems are less efficient. I’m not sure I’d bother with placing insulation around our ducting, unless I had some spare left over that needed a home (ie will you get a ROI from paying for and installing additional insulation?).

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Uber Geek
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  Reply # 1982044 23-Mar-2018 12:52
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They may produce ducting with higher R values. I don't think it would be easy to retrofit, as insualtion can be heavy vs the foil ducting.

574 posts

Ultimate Geek
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  Reply # 1982050 23-Mar-2018 13:21
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Its an existing system.


But yeah this is what I was thinking (ie the weight) and also whether there is any cost benefit/ROI from upping the R rating...because damn it gets hot/cold up there. :)

329 posts

Ultimate Geek
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  Reply # 1982489 24-Mar-2018 11:29
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If you're going to use it for cooling then you must insulate the supply air ducting and the insulation must have a vapour barrier on the outside. The usual way is to use pre-insulated flexible like Temperzone Flexiduct or Holyoake Spiroset.  If you don't do that then you're going to have wet ceilings.


168 posts

Master Geek
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  Reply # 1986579 31-Mar-2018 21:53
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All ductwork in your ceiling space should be insulated if moving heated or cooled air. The insulation and air tightness are critical to the efficiency of the system. Flexible duct is made up of an inner duct that is air tight then a layer of insulation then an outer sleeve that protects the insulation and is a vapour barrier.

Flexible duct can come in various insulation thickness, for example:
DUCT INSULATION: R0.6: Polyester 40mm; R1.0: Polyester 70mm; R1.5: Polyester 110mm

From what I’ve seen/know most companies installing ducted A/C units use R0.6 flexiduct (cheapest) I think the NZ Standards (can’t reference it now) requires R1.0 in a roof space. If it was my house I’d use R1.5.

From what I know, most A/C installers won’t even offer or advise there is a better more efficient product but I don’t know the sales process of most companies.

It would be difficult to effectively add extra insulation to flexible ducts. Probably easier to change it for higher insulated flexiducts. Problem is that the thicker insulated ducts will be harder to install.

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