Where Failed Flex Ducts in a Crawl Space Were a Magnet to Mice and Rats

This is what happens when R19 kraft-faced batts are stapled to floor sheathing, in a crawl space with framing 4x8@48, so hard to insulate. Twine everywhere just densified the jungle. It was much worse before a couple of rounds, carting away fallen-down batts; really ugly.

Many generations of mice thrived atop the kraft facing and in falling-down caverns.

Half of the batts did not share this decrepitude, sadder then to pull them down for disposal.

About 1200 gallons of compacted batts were sent off to an Eastern Oregon landfill, via this transfer station and rail cars. This is one carload of 250 gallons, a crime, but nothing compared to a mountain of plastic foam that should have had an alternative use.

HVAC ducting came into view, this an awfully-leaky 14" return line. All other ducts were Thermaflex flex, far more to be hated, as probably the major cause of the vermin infestation, the magnets of the post title.

The flex ducts were to be hated for their thoughtless construction. Here a duct is partially detached where it stressfully ducked under a water pipe.

In imagining how to craft vermin-proof new crawl space insulation, consider a romex lead to a living room floor outlet. A competitor suggested  spray foam, nicely ruled out by the wiring obstruction. At about this time I would confront a ruined very-expensive home in a  sad bid visit, uninhabitable due to stink of foam, white hardness coating even the ground.

Horrible decrepitude of the flex ducts was not easily seen. A Northwest corner of the crawl space, least accessible, was littered with rat traps. Why?

Where my discoveries began in Mid-July, 2015, my mandate was just to fix the ruined insulation. I spent part of a day pulling down batts. Then I brought lumber and insulation, to try out a method that had been on-my-mind for years. Here it is:

And with adjusted attitude and method, it works. But, what of interfering ducts? I'm told I must cope with them. I have impending family travel, and a Summer of air conditioning is wanted. I will return, and will find workable paths, in Early-October.

It is late-September, and I will attack the ducts, not really authorized. This is the near duct I had crushed, thought to be attached OK. The liner has a leak, but there is much worse. See the detached spring coils? All Thermaflex ducts in this home are of an early, brittle polyethylene formula. Wires are detached. There are associated liner rips, everywhere.

I expected decrepitude at the thoughtless runaround of laundry water pipes. Curse that damned "duct tape!"

See lots of leakage in the steel piping. See a large separation in the plastic liner, that had been hidden but not blocked, by insulation lining.

See more detached wire, and holes everywhere, inside the flex duct.

Everywhere, is not much exaggeration.

A D-box is a hydraulic monster, itself with usually-leaky attachments.

Incredible.

And, Thermaflex will poo poo, chemistry from mice somehow caused this.

This was the main entry to ducting by rats and mice, then having access to the house interior. The foulness of the liner is evident. Yet a pest abatement contractor spliced in an oversize aluminum flexible duct as the sufficient cure years ago.

Within the insulation lining, not before explored, I found this. The stick was within the air path. With the report I found immense home owner gratitude that I had insisted on demolition and re-imagined ducts.

Crude D-Box tab-in collars can not be sealed.

An insulation-lined turning box replaces the D-box. Use springy lumber to gently find alignment.

A found strap is useful, the rest of the demolished D-box is recycling.

A 16-12-12 wye was an obvious need in this alternative to ridiculous job-hacked D-boxes. Aligning it for clearance of a nearby post is challenging. Begin to see thick flexible grout coating inside all unlined steel fittings, to isolate them somewhat from temperature cycles of carried air. If the steel does not fully swing with air temperature, it has important reduction of thermal mass. Most of the volume in flexible grout is insulative ceramic microballoons.

In a chosen wye orientation, bring on insulating wrap, and secure fittings with screws and UL181 Foilmastic tape.

Some of the weight of steel components is borne by cantilever from the turning box and furnace. Most weight is carried by taut wires at joining pieces.

In advance of each joining, pull on ample lengths of insulation jacket. Jacket should fully cover all steel and insulation.

Work now with the left-side 12" branch of the 16-12-12 wye. There is a quick 6" wye take-off to a register.

Note the excess liner lengths needed to contain all steel, insulated, out of sight.

Please rely on this diagram of the as-built ducts, to locate the work in following photos.

This attachment to a 12-12-6 wye is with necessary change of direction. Pull quite a bit of tension to limit flow resistance. Call the axial taping strain relief.

Here is finished appearance at the 12-12-6 wye, in a high-traffic area. Interleaving insulation and wrap from two directions can be bumpy.

This is the previously-hated low Northwest corner of the crawl space, close up. Leaving at end of an October day, the furnace is back on and all but two registers are served.

Back in the Northwest corner, for some clear-headed, intense duct construction.

Ducts all done, but to rework a branch warming the kitchen. I will leave some of this now-dirty OSB, though I don't expect ever to return.

Here is the Northwest corner at a distance, now not foreign or hated. I see the rocky dirt as dry. I will not bother to pull up ill-fitting black visqueen, over the rocks and concrete piers.

Survey the completed ducting, starting at the furnace. Yes, there is a rat trap down there, never to be needed again, soon to be gone and forgotten. Everywhere there is smoothness overhead, and I have been under there in the duct-running.

North wall alley. Just duck under, to get past the furnace.

The 16-12-12 wye at the furnace nicely split about a post. All weight is tied by wires to the beams above.

The 12" branch toward the kitchen is pulled over vent piping, off the ground, without much flow resistance at a formation to oval.

The house had a single 7" register for the kitchen, laundry and a little bathroom. Sadly resigned that can't be improved, minimize resistance to the 7" register, new, firmed-up. 8" flex duct transitions through a 7" reducer.

Kitchen HVAC duct finally done. In the distance, I will now finish an obstructing 6" duct from the kitchen grill and fan. Overhead see another approach to hard-covered vermin-proof crawl space insulation using rips of OSB.

A determined recycler, I took apart ducts belatedly hauled from the job, too dirty and bulky for hauling with bagged insulation trash. Recycle all metal, including spring coils chopped to about 12" lengths.  Take a pause. Send that rat ridden end above for examination by Thermaflex in South Carolina.

Thermaflex was nice, accepting a length of the brittle liner for examination at my cost, against accusation failure is general; a cause of mouse and rat access, not a symptom, surely this not the only instance. To my shock and dismay, they would disagree with me, blaming mice as cause of embrittlement. And, they offered no comment whether current production is with better material.

Sharing this blog post then with Thermaflex, I studied their product claims. Theirs are guaranteed for ten years, said to be better than with competitors .These had "served" perhaps 25 years. What are we to expect past-warranty? Have materials improved in current production? We need to know these things. 

Let's have some discussion here. What have others found? Will a manufacturer speak up about materials evolution?

I suggest to Thermaflex that I am worthy as a commenter, for teaching good flex duct installation practices. May we talk about this, too?