I live in an apartment style condo that is approximately 60 years old. A month ago smokers moved in directly downstairs from me. The smell is horrible, so much so, that a friend came over last weekend and asked if I had started smoking! I already have an air purifier that runs on high 24/7 and I think it helps, but not nearly enough.

Our condos have separate HVAC units, but their air is making it into my ducts anyway. I noticed the smell was blowing into my home via the heat vents. I upgraded my filter to a 1500 merv and the smell is still there, but it's it's a little better.

I also realized that the smell was coming in through the intake vents when the system wasn't running. The air blowing in the intake is horrible...like sitting directly next to a smoker. So, I started running the fan 24/7 just to keep the place pushing air OUT the intake vents, instead of into my unit. Even though that blows air in, at least it's filtered air, not direct, second hand smoke.

Two questions:
- I keep hearing that the higher MERV filters are not good for the furnace. I'd like to go higher to eradicate as much of the smell as possible, but would that damage my system?
- What is the risk of running the fan all the time (aside from a higher electric bill?)

Any other suggestions? Ideally, the ducts would be repaired, but sealing up my return ducts would require tearing apart the downstairs neighbor's ceiling (I have concrete floors) and I'm not paying for that expense...and it will be a heck of a battle to get the smokers to pay.