Metal flexible ducts for HVAC?

[msteger]

I ran into this the other day.. Saw a 1960's style furnace with about half of the house (visible in the basement) supplied with metal flexible ductwork, the same stuff used for venting clothes dryers. Never saw this material used for this application before and called it out as non-typical installation. Plus, the ducting in the basement wasn't insulation anyway, so another reason to replace it with the proper materials. Ran the furnace and these suckers got pretty darn hot!

Anyone else out there seen this stuff for HVAC supply duct work?

[Phillip]

I have seen it a few times. It is a heaver gauge of metal than the flex of a dryer vent. If it is installed properly it will be all right. That means that it needs to be stretched out to it full length and properly supported. Joints properly sealed and the ductwork insulated.

[John Dirks Jr]

What was the diameter of the flexible ducts?

Also, you mentioned that it wasn't insulated in the basement. Many basements are air conditioned/heated along with the rest of the house and you did not mention if this one was or not. If the basement is "conditioned", the ducts do not need insulation.

[msteger]

The basement was not insulated and is mostly finished. The only place I could see the HVAC ducts was in the utility area (water heater, furnace, electrical panel, laundry) of the basement. The metal flexible ducts were approx. 4" diameter and did not appear to be any stronger than what is used for clothes dryers. The basement (since it is heated) is conditioned. Some of the ducting hung down enough to bang me in the head, so it wasn't fully supported either.

The installation looked very 'hoakey' and there were many other issues in the home, so it appeared this was also a non-professional installation. I had never seen this type of plain metal flexible ducting before until this one. I called it out for professional evaluation and clean/service the furnace since the adjacent furnace apparently hadn't been serviced in the late 1980s.