The apartment I am living in has a nasty odor coming from underneath the furnace/ac and water heater. The air for the furnace is sucked up from this underneath section making all of the air that is sent through the vents have this mildewy,musty odor throughout the whole apartment. Even if the air is not on if you open the closet door that houses the furnace/ac and hot water heater tank you can smell this odor and if you open the vent below the flooring of these units you can really smell it.

Is there a way to add on some type of extension to the “air intake” area so that it sucks up air from inside of my apartment to blow through the vents and not such up this nasty air below the unit and behind the wall?

Is this setup safe? Is the setup that the apartment has now against building code? Or a health department violation? When I have had maintenance here before they pretend like they do not smell anything however every guests I have had over has mentioned it and when I show them where I think it is coming from they agree that it is very strong in that area.

Pictures will help you get a picture of what is going on.

If I cannot add an extension to pull air from inside of my apartment than what can be done because the air that is being sucked and pushed through the furnace/ac makes the whole apartment smell moldy, mildewy, dusty and dirty and sometimes emits an ammonia odor.

I have tried using a carbon filter for the A/C filter but it does nothing to help the smell. I have no pets so it is not a pet odor issue on my part either.

Please help, I am desperate and so embarrassed and with the amount of rent we pay it feels unacceptable to be dealing with this odor.

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1 Answer 1


If the air conditioning is not properly drained, the condensation will drip down into that section underneath which can cause mold. I also notice a hot water tank in the area. Another source of potential leaks.
This mold can sometimes cause the ammonia odor that you are smelling.

You can try cleaning the mold:

  • Circulate Air: Use fans and dehumidifiers to remove moisture
  • Clean with water and detergent. Remove all mold you can see. Dry right away. If you use cleaning products, do not mix cleaning products together. DO NOT mix bleach and ammonia because it can create toxic vapors.
    FEMA on mold cleaning

The smell will return if the source of the problem is not dealt with.

If you have a location where you want to draw fresh air, you will have to ensure that the furnace is drawing air only from there (to keep the smell away) so you'd have to somehow seal up the space at the bottom. There are three concerns:

  1. Make sure the pipe/duct/whatever you put is not going to starve the furnace of air (i.e. you attach a 6" dryer hose to the furnace. It would be like you trying to breathe through a straw.). The motor could burn out if you do.
  2. By drawing fresh air in and not recirculating air your area will now be under positive pressure. The motor will work harder, doors might be harder to close/open, etc.
  3. In winter, you will spend more heating the cold air from outside.

Another option, since you are renting and maintenance seems to not be interested, is to seek out a tenants-rights organization in your area. You might have some laws protecting you in cases such as this, especially if the odor is found to be mold. The landlord might be forced to remedy this, or you may be able to end the lease early and find a better spot.

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