Bummer! You have the right idea about filtering the air. You are also correct in saying it "MIGHT"cause a problem for furnace but there might be ways of dealing with that if I know what type furnace it is.. Have you seen a doctor about this? I would suspect mold/mildew more so than construction dust. Is your furnace gas or electric? Do you have central cooling on furnace? Do you have a heat pump? There are ways of dealing with this but I must know more about your hvac system. How mehanicaly skilled are you? Have you replaced any parts on a car, ac or appliance before? For starters,buy a pleated paper furnace filter that fit's correctly. You can also buy free standing room air filter units that simply plug in similar to a box fan. Using one of those in your bedroom (LR to if you are home all day) will help a lot. A whole house or whole room device works best but a small personal unit can do a world of good. To use a personal unit,direct air flow toward your head so you are breathing filtered air.

OP, do you have metal ducts or flexduct? If metal is it internally insulated? If you have flexduct, it could be torn internally and blowing fiberglass particles. With internally insulated metal you could have a similar situation or, perhaps more likely, mold (this could be present in any duct system). Where do you live?

Filters on each supply register could help diagnose the problem and alleviate your symptoms for a while. A long term solution would be more invasive.

I don't know why you are pinning this on the ducts or the HVAC system at all. The fact that your rashes go away when you are away mean only that it could be anything in your house. How about the newly-installed stuff in the remodeled kitchen, drywall, appliances, paint, wall paper, flooring,.... It might not be any of that, but something else that you introduced into your home that you are forgetting about.

come to think of it... was the drywall you installed 'Chinese drywall' by chance?

Drywall was my first thought too. So many people near me suffered a second hard blow after post-Katrina rebuilds that I will never forget it. I am willing to bet that people now test lots of drywall for sulfur and other bad stuff before they distribute it, but I'd probably find out before buying.

I think you need to first go to an allergist and find out what it is you are sensitive to.

Ionized/Austin: It's called "process of elimination".

Thank you all for the comments and help. I see that I have not provided enough info.

@Klem1: Gas furnace, central air and heating (not a heat pump), metal ductwork with outside insulation (if any). We are very handy (we did the entire kitchen remodel, drywall, concrete countertops, cabinet making, duct work, electrical work, etc. ourselves. We currently have a washable furnace filter, and we have kept it clean. Do you think we should replace this washable furnace filter with a paper filter? I have tried using two standalone filter air purifiers for several hours per day while I'm at work (we live in Northern Virginia and it's too cold to run them when we're home right now). That didn't seem to help. We live in a townhouse, and I also tried to block the air to my bedroom by closing the room vents and directing the furnace air to only the 2 other floors. I also vacuum twice a week and dust once a week. My dyson picks up more stuff in the canister than expected, considering we have no pets, no kids, no shoes in the house, and it's just two people living in about 2k sq ft. But, I didn't try to monitor this before the remodel, so I'm not sure what's a normal amount of dust/dirt in the vaccum. I've had this problem for years, so it's not a seasonal problem. But, the remodel took years, and we recently finished and cleaned everything up last summer.

@Austin Air Companie: The house was built in 1998, so I assume the furnace is since 1998. The duct cleaning I got included cleaning coils in the furnace. Are there more than one set of coils? I lived in the house for 8 years before I started to have problems. I believe the start of my problems coincide with when we started remodeling. I suppose mold could have coincidentally started at the same time. Can I test for mold? When you say "the system is drawing in air", is this outside? I am not sure if the drywall was from China. I got it at Home Depot. Is it labeled?

@sktn77a: We have metal, non-insulated ducts. We live in Northern Virginia.

@ionized_gw: I did think of that. I can only rule out one thing at a time, so I thought I would get the air ducts cleaned, since I know we were not good at dust maintenance. I just remodeled, and it would be awful if the things I just installed were the cause. Also, there was a period in the Fall when I did not have any rashes while at home. During this time, the A/C didn't turn on b/c it wasn't hot enough, and we hadn't turn on the heat yet. This is what made me suspect the air ducts, or at least the system.

@weedmeister: I have been to an allergist a long time ago. I got a prick test and the test where they tape things to your back. I am allergic to a lot of things - mold, dust, ragweed, pollen, animals, grass, gold (yes, I know), propylene glycol, bacitracin, neomycin (the stuff in Neosporin), etc, etc, etc. Can an allergist test for drywall or drywall components?

I forgot to mention that I used the 2 standalone air purifiers for a few hours everyday. However, I didn't think this was helping b/c I did not see a decrease in dust. My TV cabinet is a large, flat, dark surface, and I can monitor the dust accumulation. After a few days or once a week, I run my finger on the surface, and I see very fine dust. But, I didn't do this before the remodel, so I don't know what's normal. I did not see a change in dust accumulation when running the filters. But, maybe I didn't run the filters long enough for the size of the room or the HEPA filter ratings are not high enough...

If something from the reno got into the ducts and is now coming out, it would have bothered you while it was going in, while you were in reno phase. Cleaning the ducts would have removed a lot of it. So you should have improved some after that if you are not saturated on the dose-response curve.

When Austin mentioned drawing in air he was probably referring to pressurization and depressurization that results from unbalanced air flow. With ducts outside of the house envelope, leaks in returns tend suck in air from outside and pressurize the house. Leaks in outdoor supplies depressurize the house and air is sucked in through random leaks. You can depressurize individual rooms anytime there is not balanced flow in and out of them (return path does not match supply). I hope that the duct cleaners did not mess up your ducts causing leaks.

Portable air cleaners. last time I did any reading about them, do little to nothing. I am not surprised at your result.

This book has helped some people: Jeffery C. May, "My house is killing me".

sktn77a: magic 8 ball says 'I am only good at guessing, I am not there.'

A couple of things: The drywall should be marked somewhere, but you may have to remove it from the wall to find it. Another option would be to check with home depot to see if they ever bought any Chinese drywall during the time in which you bought it.

System draws air: The return draws air from where ever it can when the unit cycles on. This is more common when the return is undersized, the blower acts as a vacuum pulling air thru cracks and crevices in the return. Because you're in a townhome it maybe being pulled from a neighbor. This depends on many things, how the air return was designed for the home among other things. In older homes it is fairly common that builders built chase returns and sealing them was rarely done back in the day.

Supply plenums are typically insulated on the inside of the plenum. That insulation can become very nasty and home to countless allergens. If that is the case I doubt cleaning it would do much. You would have to open it up and inspect it. If it is insulated and aged, the stuff will just crumble in your hands... enough to gag a maggot.

Ikljunky,we attempt to discuss this often in one form or the other but usually when someone move's the ball foward someone else shout's foul, throw's a flag and move's the ball back. It's up to you sorting out benificial advice from needless low bush crowing. I take it you are not hiring a pro to come in to help unless you can prove it's necessary. With all your allergies you needed a 4"pleated filter 10 years ago,install or hire one installed now. That alone could solve this once and for all. Washable filters don't catch things smaller than feathers, are a pita to clean so most people don't. Close all doors and windows,set central fan to on then crack a door leading to yard open 2 inches. Hold a smoking incense next to crack in door. Is air rushing through crack? Into or out of house? Is rushing air strong enough to farther open door or pull it closed? I see little reason to catalogue all the possabilities just now,do this and report back.

Rashes from ductwork that you are not in contact sounds odd. Are you wheezing as well? Are you using anything new that you dont take with you on vacation? Does your neighbor have cats and do you share a w/d or duct system? Could it bed bugs? A piece of furniture or blanket with wool in it? I think you should see an allergist or dermatologist.

I had a similar problem that only occurred at home, asthma attacks. It took a while, but I had developed severe allergy (hard to believe) to hamsters. Had son remove his pets, and no more problems. The only allergy I have.

@ionized_gw: Yes, I had allergic reactions throughout the reno. Reno took a few years, had allergic reactions the whole time... Reno finished and we tried to clean everything (including the ducts); allergic reactions much better, but just not gone. It was gone for a few weeks in the Fall when the heat and AC were off. But, we can't keep the heat and AC off forever... Thanks for the book recommendation.

These things can be tough to solve.

Considering the fast dust accumulation even after much cleaning, I would suspect you have a disconnect somewhere which is sucking dust into the system and distributing throughout the house. This idea is also in line with the fact that you only have symptoms when the unit is running.

It might be helpful to use a standard pleated filter instead of the washable one, change it out every couple weeks. Perhaps the washable filter has lost its static charge and isnt catching much.

If there are live microbes growing in the system, they will come right back after killing them unless the base problem is remediated. As for continuous UV treatment, I have never seen a study that indicates that it is useful.

I think you should use some advance technology air conditioning machine for which you can get rid of this problem. So try this once.

I late to the conversation but did you ever find the answer?