Ductwork Replacement


Old 11-01-10, 10:53 AM
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Ductwork Replacement

Hey guys,

just about winter here and we are looking into replacing our old ductwork, for several reasons. #1 it is quite old (the house itself is around 70-80 years old or so), #2 it has been painted inside by old owners and this is peeling amongst other dirt and #3 there is some areas with asbestos wrap.

We are having some trained asbestos professionals to come and estimate removal of the asbestos sections - there is not much. Once the asbestos is removed, we want to save money on the removal of the old ductwork and installation of the new.

So I figure, with the asbestos safely gone it shouldn't be too hard for us to tear out the old ductwork, right? Now for installation I am not as sure... I assume that I could do it all myself but it would be challenging. So I was thinking at the very least I could install the basic runs myself and mount them into the basement ceiling and have a contractor come and do-up the connections where needed, no? Would flex duct be easier for a DIY job or metal duct still recommended? Part flex? Educate me guys!

If we had more money available, we'd let a pro do it all but finances necessitate that we help out to reduce the financial burden where possible.

Also, here is a picture of one of our registers.

This one has asbestos wrapped on the outside of the register boot in the wall, behind that black area. It was sprayed with spray adhesive to encapsulate the fibers after it was unintentionally disturbed by a negligent contractor during a bathroom reno. I will ask the pros this when they come to estimate, but I thought I'd get your opinions too. It would probably be better just to make sure the boot is well sealed off instead of having the guys rip it out and potentially cause more disturbance, right? And then perhaps just installing a new register in or around that one since these old registers had very big openings.

One final question. If all goes well and we get the new ductwork installed we also want to install a HEPA bypass. Any brand recommendations? And if we do install a HEPA bypass, since it is only a bypass, can we also run just any other random media filter in the filter area before the furnace?

Many thanks guys,
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Old 11-02-10, 03:26 PM
Join Date: Mar 2006
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So many questions, I'll try to give you some answers and some things to think about.

First of all, this is the wrong time of year to be making major changes to your heating system. I strongly urge you to tough it out until spring and do the work when a lack of heat isn't a problem.

Just because ductwork is 70 to 80 years old is not sufficient reason (in my opinion) to tear it out and install new ductwork. What might be a good reason is that in your house the heating ducts are all in the interior walls with return ducts at the outer walls. This is contrary to the thinking of heating engineers of the last 50 years or so. With the heat in the center of the house you WILL feel cold drafts from the windows, even if the windows have recently been replaced. There will also be a noticeable temperature difference between the center of the house and the outside walls.

If you are willing to do the work to use the concept of perimeter heating, that is, adding the heat to the outer walls and the returns will take air from the center then redoing the ducts will have a tangible payback in greater comfort but replacing the ducts in the original configuration will result mostly in depleting your bank account.

You state that your ducts are painted inside, is that for the entire length? Are you sure a previous owner did this and the ducts weren't made this way? Or do you mean that the first foot or two from the outlet is painted?

Asbestos, when properly sealed, is not a serious hazard when left in place. Removing asbestos can, in fact, be a greater hazard than simply sealing it and leaving it alone. Proper asbestos removal is quite expensive if there is anything other than small (a few square feet) in isolated areas with good access.

Removal of the old ductwork is mostly just hammer and crowbar with maybe some compound action (aviation) tin snips to cut some of the larger pieces. Disposal could be a problem because scrap metal dealers don't want sheet metal because it takes up too much space for the weight and hauling it to the local dump will likely take many trips for the same reason. The local dump will charge you the minimum fee and for several trips that will add up quickly. A junk hauling company (there are a few national franchised companies) will also charge a high fee because of the same reasons. The more you can compact the metal the lower will be the disposal cost and you just might be able to convince a local metal recycler to take it for free.

Doing the new ductwork is not something I would suggest that you attempt unless you have sheet-metal construction experience. I also doubt that you will find any sheet metal contractors that would be willing to work with you in completing a job that an amateur has started but I could be wrong.

That register you picture most likely has been painted with a paint containing lead.

I don't know what you are referring to with the term HEPA bypass. You cannot usually use a HEPA filter in a heating system because of the high pressure drop across the filter. If it were installed in parallel with a high efficiency media filter the HEPA filter would be almost useless. Perhaps you mean a HEPA filter with its own blower arrangement that use the heating system ductwork and runs only when the heating system is off. I would not recommend ANY kind of HEPA filter arrangement for a whole-house filter because HEPA filters are quite expensive and the power to operate the blower needed to force the air through the HEPA filter is substantial.
Old 11-03-10, 10:42 AM
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Thanks for the amazing response, I really appreciate you taking the time to write all that out!

I think we got a little overly concerned and basically the asbestos consult that came assured us about the safety of the house. It would be more difficult to change those boots with asbestos than to leave them - despite their damage by a contractor in the past, they've been encapsulated for quite some time and the material, being on the outside of the duct, doesn't pose a risk.

We are however having one short section of duct about 4LF removed - it is wrapped in asbestos and is a return air duct. That doesn't make sense - and since return is negative pressure we want rid of it. Since the section is small, the contractor is removing the entire duct. This means that the asbestos is not being directly damaged, making for a cleaner and cheaper job.

Following that, we are going to have the ducts cleaned by the same company. They are the only NADCA approved company and use a compressed air whip system which I have read is significantly more effective than roto-brush or other systems.

About the HEPA, I am speaking about the Honeywell F500 whole house. Although some people don't agree with them we really like the idea. I do have questions about it though.

- should I have it installed INLINE or INDEPENDENTLY?

- what would an indepedent installation look like? Does this mean running some new duct lines that pull air and feed it back into the house or just tapping into some supply lines. Examples please!

- should I have it run 24/7 or be activated by a sail switch (this may depend on the answer to the above question).

The bypass installation requires installation of a return and supply into the return of the furnace. Basically it makes a loop and activates when the blower activates. Or it can be done independently. I'm unsure of how that would look. Does that require new ductwork?

Thanks so much once again,

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