We're moving into a 2007 built home next week with flexible ductwork and lots of cat dander. We've replaced all the carpet with tile and will purchase a dehumidifier. For the central air - To make it low-allergy for us, we're planning to install two UV lights (before and after plenum), install an IQ central purification system, and replace the ductwork with galvanized steel. We have someone who can do it reasonably. Is this a good mode of action for us? They're planning to insulate it with the standard foil covered "tape" insulation. They do not have knowledge of "green building" and we're new at this.

UV is useless. Especially against "cat dander".

How "tight" is the house? Has a blower door test been run on it?

The UV lights would be for keeping the plenum free of mold. The IQ air purifier would cause only filtered air to run through the system so that should filter out the cat dander. Not sure how tight the house is, need to get a blower door test done.

It's just easier and more cost effective to clean the plenum once or twice a year. Mold requires moisture so not sure why there would be any in there.

Where is this?

I'd use HEPA filtration and never let the house go to a negative pressure (which would pull in allergens without first passing through filtration). I suppose it also depends on what someone is allergic to. I might even treat with ozone (with the house unoccupied).

You might try cleaning and sanitizing the duct before going through the expense of replacing it.

Read from the Healthy House that condensation (precurser of mold), can build up in the folds of the accordian style ducts. The "pleats" are very hard to clean out. We're in Ft. Worth - very humid area...

How do you avoid a negative pressure in the house?

If the A/C is working properly there shouldn't be a humidity or condensation problem in the ducts.

> How do you avoid a negative pressure in the house?

Proper balance of the hvac system in each room. Beyond that, a fan blowing inwards, through a filter. Preferably controlled to just what is needed under current conditions (the authors of the link may know of specific equipment).

Some HRVs can be adjusted to balance for typical conditions.

I agree with keeping humidity low. Buy a humidity meter and check everywhere. For example, the outside of a cooling duct may hold moist dust.

Thanks for all the info - very helpful. How do I keep the house from going into a negative pressure?