Reducing Noise Between Units (Air Ducts)

5 Replies

I have a single family home that is being rented out as two units. The tenants have mentioned that they can clearly hear each other through the vents. Any suggestions on things I can do to reduce the noise between preexisting duct work?

@Sam Valme

You can insulate around the ductwork to deaden any sound travelling through it, but if you are going to open walls and ceiling to do that, you might as well separate the ductwork. 

Ductwork between units is also a conveyance of germs & odours and a potential path for fire.   

@Sam Valme ... units built for one purpose, then used for another, sans a proper conversion, are ripe with problems.  As @Roy N. mentioned, there are methods which may deaden sound transmission through the ductwork, but they're band-aids where stitches are more appropriate.  Curious, so one tenant controls the heating/cooling for both?

Keep in mind, that once you fix the ductwork noise problem, they'll likely notice the noise through the walls/floors since those weren't designed for separation either.

@Account Closed , I definitely appreciate the input! This was briefly mentioned by my wife as a concern for us renting out the house. But after talking about it more and the added costs. We've deemed it a minor issue in comparison to some of the other changes of the home. 

@Roy N. , do you mean install another furnace and AC, or just separate the ducts while keeping one unit to circulate the air? Installing another furnace+AC will be quite expensive. Will it help to reduce the noise noticeably if duct work is separated, but meets in the single furnace/ac unit?

What would you recommend as insulation around the ductwork, is there a product that can be painted or glued over the ducts?

@Sergey S.

Shared ductwork is a corridor for sound, odours, viruses, pests and a path for the spread of smoke and fire.

Separate furnaces would be the best solution.  This could be combined with an effort to put the utilities back in the hands of each tenant - as opposed to having the landlord carry the costs of a common heating system.  In such a context, it may not be expensive at all - we've had payback in as little as three years.

To air seal ductwork - which is arguably more important than insulating - you can use appropriately rated ventilation tape (foil-based or other) or mastic.  To insulate ductwork, there a various kinds of wrap insulation (from foil faced / bubble, to mineral wool or fibreglass blankets) or, if in a wall cavity, ceiling or bulkhead/soffit, you can simply pack mineral wool insulation around the ductwork.   To simply deaden sound transmission or harmonic vibrations, there are peel-n-stick sheets and wrap - similar to what is used in automotive applications - which you can use if you have a particularly noisy section of ductwork.  Cork-based sound deadening sheets may also work.  You will need to confirm whatever product you select is rated to handle the heat to which ducts can rise (which is relatively low).

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