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5 inch insulated heating duct

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  1. #1
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    Default 5 inch insulated heating duct

    Hello fellow renovators,
    First time poster yet long time reader here. After seeing some other members having successfully replaced some old central heating duct work, I decided to give it a go myself.
    I ventured under the house yesterday to remove the old insulated perforated semi rigid duct work (I guess it was installed about 1980 going buy the heater manufacture date). I found it was crushed in 3 spots (single duct), and many rips in the outer plastic.

    After removing it I measured up and went online to consider buying replacement but I found that mine was 5 inch (125cm) and that seems hard to find, with 6 inch (150mm) being the common size.

    Can you still get 5 inch insulated duct work? was this only common back in the 1980's and now is no longer used?
    I cant simply upgrade to 6inch because all the vent registers are 5 inch as are the T and Y pieces under the house.

    In the mean time I put the old duct back with lots of tape over the holes and somewhat reduced the crushed points, at least for now I have heat - just rather inefficent

    Thanks for any ideas you can provide me

  2. #2
    1K Club Member paddyjoy's Avatar
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    Default

    If you are using the flexible ducting like below I don't imagine you would have any problem reducing the 150mm inner core down to 125mm and then securing with cable tie and tape (just to be sure).

    Polyaire » Firebreak » Firebreak Duct R1.0 (Polyester Insulation)

  3. #3
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    Default

    Thanks Paddy,
    Yes i am looking at the new insulated flex duct, I was considering using the 6 inch but was a bit worried it might not be the correct way given the current metal (Al or tin) inner is a snug clip on fit.

    That said i can not find an easy supply so I assume it was an outdated size and now 6 inch is the standard. Both Polyair and westaflex have outlets near by so i might have to buy some and try it out. That is of course once my body has recovered from the 7.5hrs crawling around yesterday.

    Cheers

  4. #4
    1K Club Member paddyjoy's Avatar
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    Quote Originally Posted by Benftg View Post
    Thanks Paddy,
    Yes i am looking at the new insulated flex duct, I was considering using the 6 inch but was a bit worried it might not be the correct way given the current metal (Al or tin) inner is a snug clip on fit.

    That said i can not find an easy supply so I assume it was an outdated size and now 6 inch is the standard. Both Polyair and westaflex have outlets near by so i might have to buy some and try it out. That is of course once my body has recovered from the 7.5hrs crawling around yesterday.

    Cheers
    I'm not an expert but I'm sure the 6 inch would be fine, the slightly bigger duct might change the airflow slightly in that branch however given your system is 30 years old there are probably other things to worry about.

    The duct has a spiral wire going though it so you should be able to twist the end bit so that it reduces down from 150mm to 125mm.

    It's tough work I could never do it for a living

  5. #5
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    Hi Benftg,

    Welcome to the forum.

    I replaced a lot of my ducting a couple of years ago. You may have read my thread here - http://www.renovateforum.com/f193/du...ptions-108619/

    You should be able to get a reducer to allow you to fit the new ducting. For all my supplies I used Dual Heating in Ringwood - Dual Heating,Ducted Cooling,Evaporative Cooling, Refrigerated Air Conditioning, Split Systems,Ducted Heating Cooling Melbourne.

    I was able to get everything I needed from these guys and they were really helpful. Give them a try and see how you go.

  6. #6
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    Hi Grasshopper, thanks for the recommendation. They are very local to me so that is very helpful.

    I have indeed read your thread many times, I could basically blame you for thinking I should give it ago myself .

    I can only imagine how hard your job was, after one full day under the floor I was sore for days.

    I have 2 options:

    1. to fixed the crushed pipe and live with the old ducting given i use my reverse AC for most heating (except when its getting very cold outside)

    2. replace the lot knowing it is old, with leaves and dust in the ducting with some small holes in the outer plastic sleeve.

    If i opt for the second option i should zone it into living area and bedrooms. I guess thats one hell of a lot more work and cost, so maybe i will hold off on the full upgrade until next year.
    I just realised for zoning you need a zone compatible heater such as the Brivis StarPro, and my 30yr old Buffalo wont work with a zone system, so maybe just a simple duct replacement may increase the efficiency and get some more years out of this system yet

  7. #7
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    I opted not to zone mine even though it was possible with my heater. I guess it comes down to your floorplan and your living areas etc. My wife is home with my kids most of the time and most rooms are being used so it sort of made sense for me to just keep the entire house warm.

    I would opt to replace the damaged ducting as patching it is still going to put strain on your existing Buffalo. You're in the same position I was in however my Buffalo died before I managed to replace the ducting. I was actually surprised at how cheap the ducting is. If you are prepared to do it yourself it shouldn't cost you too much. A new heater on the other hand does not come cheap.

    Dual Heating can supply everything you need, just get yourself a staple gun to use to strap the ducts off the ground if you have the clearance. It's a dirty job but one anyone can do.

    Good luck! I still have more to do when I get the opportunity. I have to dig my way in to reach two other ducts. I ran out of time last time but it will need to be done at some point.

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