cutting HVAC vents

[myxpykalix]

I have a house where the 2 apts share the same furnace and vents and i'm wondering if there is anyone with HVAC knowledge to help advise me to design some type of vent louvers, or some type of one way trap to allow air pushed out but will close so as to not allow cat hair from the upstairs to circulate thru the system and into the basement apt since they are allergic to cats and dogs. Maybe some type of filter housing i could cut on the bot and put inline?

[Gary Campbell]

Jack...
I will help you. Code requires that each unit have its own forced air system. If a fire starts in one, it can travel with the moving air to the other. You can use a common boiler tho. Pony up for a new system, or 2. :D

[myxpykalix]

The second apartment has been grandfathered in, so that provision doesn't apply here and in 14 years of owning this house i've never had this issue but the people moving in are allergic to cats and dogs and if there is a simple fix like inline filtration or a filter housing i could make relatively inexpensive and maybe with the bot might help.

Besides i would spend more on a seperate system then i would make in rent for the year, so thanks but no thanks, lol:eek:

I have been thinking about designing some type of registers where the baffles swing open with the force of the air but shut when the airflow is off.

[harryball]

Jack, Not speaking as a professional but someone who has had to deal with allergies (my wife's) when handling HVAC etc...

The return from each domicile should be isolated and a high efficiency filter be installed. Something massive like an Trion Air Bear which was my choice. If you have room A and B then all air leaving room A should be filtered then processed (heated cooled) and returned. Same for B.

For your registers if you feel there is potential for air movement when the system is off you should install a zone system that only opens to move air to the single space. However, a simple backflow damper where needed would probably work fine and be easier. Aprilaire makes several models.

You could also put those little lint filters in the register themselves. Cheap but they do collect dust and have to be cleaned frequently.

If it were me, I'd install the filters and forget the zone or dampers unless someone complained then I'd try the lint filters.

[myxpykalix]

After getting the advice here i went down to lowes and looked around and here is what i've come up with.

With Harrys advice i got one of those expensive filters that is supposed to filter out pollen, mold, pet dander, ect.

I got some of those small filters for each vent and some cuttable filter fabric for some of the bigger square vents in the basement to try to eliminate cross contamination thru the vents.

I also was thinking about something like those dryer vents that have those louvers that open when air goes thu but close when not in use.

I did do research on your links so your help was appreciated Harry:D