# Forum Home Renovation Heating & Cooling  Best heating ducting avail

## sundancewfs

Ok lets see if the forum wiz's can come up with some answers to these questions  :Smilie: 
Where can you buy insulated, rigid heating ducting?
Where can you buy duct with an R value greater than 1.6?
Why is flexible ducting used almost exclusively on domestic install?
I have read that the maximum recommended length of flexible ducting is 6 metres ( http://www.westaflex.com.au/_pdfs/du...troduction.pdf ). Is this so?
We will be putting in a new zoned gas heating system with our renovation and the main line of the ducting will be in the unconditioned space under the floor. I wish to achieve the best efficiency possible. As an example of what Im trying to overcome, I measured the external surface temperature of the main heating duct that we have under the floor with an infared Fluke thermometer, with the heating on, last night. The air temp was 13 deg and the measured external temp on a sound piece of duct was 31. Seems like a huge waste to me.

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## AIRMAN

If your after max insulation value it's best to get fibre glass insulated duct rather than poly, its much more consistant. The promblem with poly insulation in ducting is that the thickness is very hard to keep consistant and even tho it says that it is R1 with 50mm poly in places it may be as thin as 10mm.  
Westaflex make the best quality duct (the core is mechanically locked and not glued like all other duct it also has a 25 year warranty, other have 10) but it is also about 3 time more expensive than other brands, another good thing about them is they use 70mm poly for R1 duct where as everyone else uses just 50mm (this happens because BCA allows you atribute a certain R value to the inner and outer sleeve) Westaflex will also make you R1.5 as a special order which I belive is 90mm poly. 
The reason flex is used on resi is simply due to cost and simplicity, it is use in com aswell but only in small lengths coming off solid duct runs. 
Flex only comes in 6m or 3m lengths, reason for this is that you shouldn't be running more than 6m of one size duct due to static pressure. You would normally be coming off a branch within 6m of a outlet. 
If money isn't a issue you can alway get sheet metal duct made up for your exposed area and get it internally insulated to whatever R value you like but you would be looking at, at least $200 a metre.

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## sundancewfs

Well there is some food for thought.... Thanks AIRMAN
I'm thinking of using a rigid duct as the trunk and then using flex, ducted off to the registers. Is there any companies that do "off the shelf" metal insulated ducting?

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## AIRMAN

No it will all be made to order, take some measurements and do a rough drawing, look up air conditioning duct sheet metals places in the yellow pages and go talk to them. They will charge a premium for doing such a small job. They are going to look at you funny when you ask for 100mm internal insulation as it's not very common at all. The other down side is that the insualation has to be internal as it's going out side and that mean it going to be sisal fibreglass sheets and it effectivly has a exposed face which I have never liked the idea of. 
Another option would be to use this stuff, http://www.p3italy.it alot of places sell it in aust and you can even just buy the sheets and make on site your self with contact adhesive and silicon but I wouldn't put it anywhere exposed to rain or direct sunlight. In that situation you could also explore using coldroom panels, esy to construct, very sturdy, clean and very well insulated.

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## sundancewfs

I had thought about making some sort of rigid duct from 100mm EPS, sort of like the product on the link. With our new extension and existing house rated to be 5.5 star on completion it seems a waste to have a penetration for the ducting through a ICF wall rated at R3 by a R1.5 duct.

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## Smurf

Does anyone have any figures as to how much heat is lost through the ducting? 
Are we talking about losing, say, 2% or is it more like 20% loss? Judging by some of the comments here, I'm thinking that it's quite a big heat loss? 
Just curious. :Smilie:

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## AIRMAN

There was a study done not to long ago that showed upto 50% of a domestic air conditioning systems capacity is lost through the duct work!!  
Most domestic installers don't even meet or under stand BCA Section J requirements and manufactures of domestic duct and fitting are falling well behind in educating the installers and home owners.  
When I did my house I used custom made flexible duct (R1.5+), return air in each room and put zone motors on both the supply and return in each room so the return air is only coming from a air conditioned space. I also externally wrapped all the fittings and even the unit. All of this and I did the whole house on around half the capacity your average installer would have put in.

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## Smurf

> There was a study done not to long ago that showed upto 50% of a domestic air conditioning systems capacity is lost through the duct work!!

  Wow!!! 
If the losses at the furnace are, say, 20% which would be reasonable plus 50% of what remains is lost in the ducts then that's a 60% loss all up from energy in the gas to heat in the house.  
I know that gas is a lot cheaper than electricity in Victoria and SA, but here in Tas if the losses are at that level then it works out at roughly 16 cents per kWh for heat put into the room after all those losses if it's run on natural gas (which most homes here don't have anyway). Meanwhile us Tasmanians keep arguing about the merits of heat pumps versus wood heaters, both of which work out somewhere around 3.5 - 4.5 cents per kWh - a cost that's more than enough when you've got a fairly cold climate. 
I'm surprised that these systems are so popular if costs are that high. Maybe they just aren't used enough in the warmer states for the actual bills to be high enough to worry anyone too much? I'd assume you at least get some decent heating for that amount of $ spent running it?

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## sundancewfs

It seems to me people are willing to accept inefficiencies in systems like this as they aren't told how bad it is, "its what is normally done", "we don't like using R1.5 as it to stiff and hard to work with". The last one, I was told by a couple of heating firms.
I think we need to have a more open mind in our trades, manufacturers, suppliers etc, to overcoming some of the simple fix problems that are inherent in our, for the most part, mild and moderate Australian climate. For all the talk of reducing greenhouse emissions, if there were programs to address these problems, we could reduce a lot.
I have found it very hard to find people willing to listen to my "requirements" if they exceed what is, by code, necesary or what they normally do.

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## sundancewfs

Isn't it funny when you do a search on google for a topic and you come up with your own post as one of the top seach results! 
Oh well.... 
I thought we could revist this old post though, in case there has been some major breakthroughs in ducting or insulation since it was last raised. We are now getting closer to ducting out the extension ( http://www.renovateforum.com/f176/ic...project-76617/ ) and replacing the existing Brivis Buffalo 85 central heating with a new 5 star, zoned Braemar unit. So it has become relevant again. 
In short I want to use the highest insulated, BEST quality ducting in the un-conditioned spaces ( under-floor, in roof) and a more standard R0.6 ducting between floors and in interior bulkheads.
Any new thoughts?

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## Eastwing

I have used a rigid main with flex branches, I get some of my stuff from Rayson they are good to deal with and quick.

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## sundancewfs

Eastwing,
Thats one to check out. Funnily enough I had thought of getting Raysons to do the ducting for my dust extractor.

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