Replies

1. 
   experienced | Nov 09, 2005 03:51pm | #1

   Is the duct work in the crawlspace corroded of mis-sized for the air volume it msut carry? If not it can be cleaned and then insulated.

   Have a look inside the ducts to ascertain the dirt levels. On the supply side, there may not be much dust since the supply  air is filtered. Get an experienced duct cleaning company if you decide you'd like to get them cleaned anyway,since they haven't been cleaned in 35 years  (and may not have to be for another 35 years)

   Clean the metal around all joints/takeoffs. Seal all joints and gaps at side or top take-offs with a brush-on mastic sealer. This is like an acrylic latex caulk in a can. Use a 2" old paint brush to apply. If there are gaps larger than 1/8", you may need a bit of fiberglass tape applied first as a base to hold the sealer.

   After sealing, insulate the ducts with a commercially available foil covered 2-3" fiberglass roll batt. The colder your crawlspace the thicker batt you'll want. Seal all foil joints with foil tape.

1. 
   davidmeiland | Nov 09, 2005 06:10pm | #2

   Good plan. If the existing is in poor condition it could be replaced with insulated flex duct, which is a little bit quieter.

1. 
   DaveRicheson | Nov 09, 2005 07:34pm | #3

   Or if it to be replaced, have the new duct insulated (internal) before the install. Cost just a few cents more per foot, but it is worth it. Adding external wrap as experienced described to the internally insulated duct would be the cadilac addition.

    

   Dave

1. 
   experienced | Nov 09, 2005 07:57pm | #4

   The internal "duct liner" is for sound control only. To have it inside the duct can raise future problems. For example if there ever was a water spill into the ducts, they would have to be taken apart to take the duct liner out as it surely will spawn a mould bloom by holding water. Also, you couldn't clean the ducts in the future as the liner would be damaged, releasing glass fibers into the air!!

1. 
   DaveRicheson | Nov 10, 2005 02:23pm | #5

   Also, you couldn't clean the ducts in the future as the liner would be damaged, releasing glass fibers into the air!

   You are way off base with that one. I just supervised a duct cleaning job in one of our office areas this past summer. All of the duct was internally insulated, and none of it was damaged durring the cleaning. Roughly 800' of duct was cleaned and sealed. The contractor took before and after pictures, and I did a visual inspection at each access hatch before they could seal them up.

    

   Dave

    

2. 
   Tim | Nov 10, 2005 05:22pm | #6

   I have to assume on this one that you're not actually "experienced" with duct liner. The duct liner that I sell, and that is very common in commercial applications is treated with a biocide and will not grow mold, even if its intentionally incubated with it, and it is very easily cleaned by competent contractors. As far as "releasing glass fibers into the air", this doesn't happen, unless the product is deliberately destroyed.

   Duct liner is not only for sound control, but is a common way of insulating rectaungular duct in way that is not prone to physical damage after or during insulation.  It is a very effective insulation, with the additional benefit that it is a great sound control media as well.

3. 
   experienced | Nov 11, 2005 01:15am | #8

   No, I have actually installed duct liner both with a "pinspotter" welder and with the stick-on tabs. It's only that the liner we haved used in our neck of the woods would not stand up to the violent thrashing of some of the duct cleaning dust dislodgers and many others would not also. if they are not thrashing the sides of the ducts, how are they cleaning the ducts as clean as they say they are. Or is this another part of the "smoke and mirrors" of duct cleaning. Both the US Environmental Protection Agency and Canada's national housing agency, Canadian Mortgage and Housing Corporation, say that except in special and rare cases duct cleaning still has not proven to be generally beneficial. See articles at both websites: http://www.cmhc.ca     http://www.epa.gov

   As for the biocides- Which ones were used? If you visit the Environmental Protection Agency website, you will see that not many are actually approved for ducts. Some duct cleaners were found using agricultural biocides for barns in house ducts!!! I wouldn't want to have any in duct liners period. This is the air we are going to breathe; why put biocides in it!!! Our bodies are full enough of chemicals now.

   A small study of just 11 people was released in Canada yesterday. The study did a full chemical analysis of the body for manmade chemicals and pesiticides. They found pcb's, pesticides, flame retardents from our mattresses, and on and on. No wonder that 1 in 3 of us will get cancer and that 1 in 9 women will get breast cancer, double the rate of 20 years ago. If that was testicular cancer rates, maybe more would be done about it!!!

   Also the biocides don't protect any dust lying in the bottom of the ducts up to 1"+ deep if it gets gets wet; moulds will start to grow there at the top surface of the dust.

4. 
   Tim | Nov 11, 2005 05:30pm | #12

   "Thrashers" are not used to clean lined duct by competent inividuals. Though I am not a cleaning technician, I have inspected lined duct that had been cleaned, rather effectively with no damage, with a vacuum type of process. Beyond the capability of the residential duct banger/hacks. Cleaning ducts in a properly designed, operating and maintained system is, IMPO, a waste of time and effort.

   "...bottom of the ducts up to 1"+ deep if it gets gets wet..."

   IF someone to allow 1" of dust to accumulate in a duct system, which I believe is very far fetched, mold would be the least of their problems. I have surveys a great deal of air handling systems that have been in service for decades and never seen that kind of accumulation. Mold, BTW, with the exception of very small population of people with compromised immunity systems or some with specific sensitivities, does not cause or aggravate any physical ailments. The present hysteria on this issue is unwarranted and unfounded. IT IS NOT based on any scientific or medical evidence.

   As far as the actual treatments used in commercial duct liners, I don't know what they use. Unless you plan on pulverizing the product and ingesting it, it poses no health risks.

5. 
   experienced | Nov 14, 2005 12:55am | #13

   Tim:

   15 years ago, I spent 2 years in the commercial HVAC field (actually set up and managed a new subsidiary IAQ/air balancing company for a mechanical eng. firm). Saw a few older ducts with dust/dirt as mentioned in them but no situations where I called for duct cleaning. The last one I saw was 5 years ago when a recently decommissioned school was bought by a religious organization. It had close to 2" of dust/dirt under the main return register. A newly minted IAQ consultant (3 days of training = a certificate) called it contaminated!!! I was called in and asked "What was contaminated in it and where were the tests?" No answer. BTW, the furnace had no filters installed. On my advice, the folks rented a good shop vac with extra hoses, cleaned it out and I haven't heard from them since.

   I'm like you and feel that duct cleaning has limited value but may be necessary in certain situations. I actually looked at buying into Canada's largest duct cleaning franchise system in 1985 but decided against it. Also, there is a bit of hysteria being created by the press and those who make $$$$$ on some of these "problems". I fight them on my website which I'll send privately to you.

   For myself, something doesn't compute with your last post. Every return duct I have ever seen with a few years of service has some dust in it. How are you keeping dust out of ducts......filters at every return grille/register?

   Your quote: "IF someone to allow 1" of dust to accumulate in a duct system, which I believe is very far fetched, mold would be the least of their problems." What other problems are you alluding to?

   Edited 11/13/2005 5:10 pm ET by experienced

6. 
   Tim | Nov 14, 2005 08:29pm | #14

   Dust in ducts, supply and return, is a fact of life. If I made a statement to the contrary, it was in error. If the dust settles out in the ductwork, it will stay there until disturbed. Dust lying in the bottom of a duct is of little consequence. It will not grow mold, it will not cause sinus problems or aggravate allergies. If the dust stays in suspension then it will end up in the filter or back into the space, from where it orignated in the first place. No harm, no foul, no problem. Hence my position on duct cleaning. IF by chance a non-operating system is to be restored to operation or some spill is involved, obviously some remeditaion is required. Otherwise, if duct a system is designed properly, with regards to air velocity, friction and air splitting/fitting good practices, accumulation of dust in the ducts will be very limited.

   " What other problems are you alluding to?" Honestly, I have never seen 1" of solid dust, but I would expect, if that amount of dust be allowed to accumulate in an occupied space, the extreme filth would be of paramount concern. Rats and roaches come to mind. I have seen in a system that had been in service for over 30 year, open, lined return above a pleneum-layin ceiling. A fair amount of dust had accumulated on the top of the tiles however, the lined return, though quite dusty on the surfaces, had no measureable depth of accumulation.

   Mold, contrary to current popular opinion, is also of little physiological consequence. It looks bad and can degrade the structure but healthy people are not adversly affected by mold. The conditions that exist that promote growth of mold happen to exist along with other conditions that lead to general poor indoor air quality, such as inadequate humidity control, improper facilities maintenance, poor air turnover and circulations, poor and/or inadequate ventilation (fresh air)

   The idea that dust in a duct would be wetted, to me, is a remote possibility in any system that is close to operating properly. Again, I would say if you are getting liquid inside of supply or return ducting, you have serious problems that must be addressed, wether they be HVAC system related, maintenace or facilities issues, or intrusion of water from outside sources, building shell leaks, internal plumbing leaks, etc.

2. 
   McMahon | Nov 11, 2005 12:58am | #7

   In your opinion is insulating the duct work a cost effective procedure?  I live in Colorado and my duct work is also in the crawlspace. Any more our winters are pretty mild (almost 80 today) so the crawlspace probably only gets real cold for short periods of time but with the high cost of heating I am always looking for ways to lower the bill.

    

   Steve M.

1. 
   experienced | Nov 11, 2005 02:16am | #9

   If you can do the work yourself, it will aways be cost effective. If the crawlspace temperature between heating cycles is say 65 deg F, this may seem quite warm but don't forget the heating air in the ducts will be from 120-140 or so. Metal is a good conductor...so substantial heat will still be lost to the space as rectangular ducts of 8x16 or 20 have a lot of surface area to lose heat from.

   Before you insulate ducts seal all joints and holes for air leaks.

   A bit of a side note:    If the crawl space is quite airtight and the lost heat from ducts is retained there helping warm your floors from underneath, then insulating may make your floors a bit cooler.....more heat to the living space but less to the space. If you have insulation up between the floor joists, by all means insulate the ducts!!

1. 
   johnyrrr | Nov 11, 2005 03:43am | #10

   what about fomo.com or tigerfoam.com and spray the exterior ducts with poly foam your self after you cleand them up on the outside real good?

1. 
   experienced | Nov 11, 2005 06:19am | #11

   Good idea but there may be a couple of flies in the ointment.

   The spray foams in small homeowner packs are quite expensive. Hope that 2 or 3 are not needed. The other is that the foam is flammable and may have to be covered with a fireproof coating to meet local codes.