This post absorbs still-relevant content of withdrawn post Working With Cotton Insulation Batts. At March, 2026, recycled denim as expensive wall insulation or sound treatment is a dead market. Thick batts for floor insulation are no longer sold anywhere.
Some cotton batts continue to be sold at Home Depot, labeled Henry UltraTouch. "R13" and "R19" bags under-fill 2x4 and 2x6 walls. Under-fill is from irregular thickness and extreme difficulty of cutting-to-fit. Odd circumstances are not served by powerfully-stamped perforations. Parting to pass wires is impossible. With my reporting, I seek to discourage all others from thinking that cotton batts are somehow "green."
My experience with cotton batts has relevance now, only as an element in my only experience with a deep energy retrofit.
The deep energy retrofit began right in 2008, with a ground-mounted 3.5 KW PV array. The array safely beautifies and might fully electrify a 2.5 acre farm. It seems that the now-old air-source heat bump needs expensive deep-winter electric resistance heat backup. A good ground source heat pump should now be afforded.
Proper weatherization of the home to support this early-adopter heat pump energy independence is to my credit. I hope that the air-source heat pump has never again needed backup of electric resistance heat, and that no grid power has been needed. In this there as been need of an additional investment in large battery capacity. I hope to learn soon whether all of my work has been durable, and that net-zero has been attained.
Making Right Out of Fright
So much work in home weatherization is with starting conditions that are beyond challenging.
The work is daunting.
My worker-willingness was observed as a child, where my father, a poor farmer in Minnesota who grew up with horse teams, likened me to the much-appreciated and rare
I wonder whether worker-employees can have the needed motivation. I think that, rather, unasked initiative is punished.
Fixing everything on the main floor, attic and roof took 274 hours in the Fall of 2011.
Here are the many details of these repairs as PDF captioned job photo albums:
Here are photos of main floor, attic and roof starting conditions:
Large attic floor pits exposed first floor walls to attic temperatures. Here, drywall was grouted about a chimney well.
Attic photos, work in progress:
Here are achieved conditions in the first floor and attic
174 hours of epairs in the crawl space were done in Fall of 2013
The found condition in the crawl space was blocked by a no trespassing indication.
Very heavy cotton batts hung down 6" from floor contact against twine restraint, there was zero insulation value, Brave workers persisted against common sense, and an invoice was paid. The lasting contribution was only a thorougn new Visqueen ground cover.
The found all-steel HVAC supply ducts were left horribly leaking, draped with R19 fiberglass batts. The duct insulation batts added much to a feeling of confinement. The same with R11 batts generally wrapped around copper water pipes.
See that steel duct fittings, wyes, take-offs and reducers hang from 9" rips of 1/2" plywood. after perfecting co,p;ete coverage with insulating jackets, hoist to jam an eye bolt through a 1" hole in the plywood, and pin with a 5/8" dia length of resilient farm property tree branch,
Intimacy of flex ducts with the overhead plywood rips will discourage mouse habitat, I hope. For persons, see freedom to get around, easily sliding under clean and smooth flex ducts.
CS Batts Repair Method:
Someday, say in 25 years, the flex ducts will need replacement. It will be easy to unpin the steel fittings to bridge in new lengths of duct,
Consider the energy savings in employing flex ducts vs. solid pipes with wrong assumption of zero leakage either way:
Reduce Energy Waste in Thermal Cycles Of Heat Ducts
An important feature of the new ducting is much-reduced thermal mass exposed to each heating cycle. The mass of steel ducts responding is reduced from 200 pounds, to fifty pounds.
Compute an energy savings for the reduction of duct thermal mass:
Assumptions:
Crawl space at 200-day heating season average of 50°F.
Average air temperature within ducts in a cycle is 90°F.
Wrapped ducts heat inertia is such that temperatures are followed 50%.
The furnace cycles every half hour, 48 times per day.
The total mass of ducts is reduced from 200 pounds, to fifty pounds.
The temperature change of the total mass of heat ducts is 10°F in each cycle.
The heat consumed in each furnace cycle is:
m * Cp * delta T
where m = 200 pounds mass, or reduced to fifty.
Specific Heat Capacity, Cp = 0.12 BTU/pound/°F
delta T = 10°F
BTU wasted in each cycle: 200 * 0.12 * 10 = 240 BTU
Times 48 cycles
Times 200 days
Result: 2,304,000 BTU per year
Times 0.00001 to convert to therms, is 23.0 therms.
Times $2 per therm is $46 per year.
At fifty pounds, this is reduced to $11.50.
Energy savings now with flexible ducts are $34.50 per year, not counting benefits of real duct insulation. I think wrap of unfaced fiberglass batts loses most of its value with air circulation.
I think this is a fair estimate. Under $50 per year is saved. Even with insulation wrap, the steel components without an interior liner may cycle by more than 10°F. However, the number of days and cycles per day, may be high assumptions for this home.
Please just recognize that lower duct thermal mass is a good deal, comparable to benefits of stopped leakage and of keeping fittings and flexible ducts aligned for least flow resistance. The prospect of much easier replacement of flex ducts terminating at fixed-in-place steel elements makes coping with flex duct failure more bearable. Be happy to have ducts renewed, clean. every 25 years
Study Details of the Ducts Hanging From Steel Elements
6" Chamfered Straight Take-Off From 12"
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