Best fix for a constricted heating duct hose?

[therockdoctor]

I recently noticed that my ducted heating wasn't working as well as it used to at various points in the house (very low air throughput at some outlets compared to others). A quick inspection under the house has revealed the cause - one of the main ducts off the heater (heading to the points with low air output) is severely constricted, coincidentally after a sparky was recently working under there... It looks like the duct (the flexible type) was sat on for a while and the metal rings inside the duct have now settled themselves and won't squash back to their previous circular form to open up the duct again.

So, what are my options here? The constricted section is not far from a branch point so I could remove the duct at that end and pass some sort of rigid piping through to the constricted section and force it open again (maybe a metal sleeve or PVC pipe of some sort). Or should I just replace the entire section of duct? It's about 6 metres from one join to the next. How much is such ducting (it's 300mm) and where could I get it from? Also how hard is it to achieve an airtight seal at the branches with duct tape?

Thanks for any advice,

Lee

[johnc]

If the crushed section is small you could possibly get a suitable metal joiner, cut out the offending section and insert and tape the join. Alternatively replacing the complete section or part there of will fix the mess. The bits and pieces are fairly cheap and easy to instal.

John

[Skew ChiDAMN!!]

Go through the green guide and look up places like Cosi-home, etc. that do naught but sell/install aircon & heating. They'll normally be more than happy to sell you a length, make sure you specify that it's for ducted heating. Naked duct (for aircon) is a lot cheaper but doesn't have the insulation. Be warned, there're some cowboy outfits out there who'll just as happily rip you off, so ring around to get a few quotes on duct. Also, as John said, you can buy couplers to join lengths of duct. It's usually cheaper to replace the length than to buy the couplers though... or it was a few years ago when I was dabbling in the trade.

However, IF you have enough length to cut out the damaged section and rejoin what's left without disturbing other branches or reducing bends to less than 3' radius then a coupler is the way to go. It'd actually improve on the original flow! Some installers can't be bothered trimmimg to length, with results that're less than optimal. Like I said, plenty of cowboys out there.

An air-tight seal with duct tape? ROFL! That's what it's for! When taping up simply push the insulation/outer cover back about 6" so you can access the internal duct, which should be a very snug fit over the branch and may take some careful persuading to slip into place. Tape it on, running the tape around several times. Pull the insulation and outer sleeve back up over what you just taped and also tape that into position the same way.

Job finished in less time than it took you to read this post.

[GraemeCook]

I am with Skew on this one.

Duct comes in three and six metre lengths, so you'll probably get more peace of mind by replacing the damaged section. Also consult yellow pages for suppliers - I put in a heat pump ten years ago and got ducting, etc from Bradfords but I have been told they no longer sell to the public.

As Stew says, its essential that you use the insulated, not the cheaper naked ducting, and its also worth paying marginally more for the accoustic rated stuff. It will marginally quieten your system.

Cheers

Graeme