The Pressures of a Stinky Mind

Condo Entrances

Condo Entrances

When you’re living right next to someone and they like to smoke and you don’t, the situation can sometimes get nasty.  When I was in college, I lived over a guy who worked as a DJ on weekends and he had some pretty powerful stereo equipment that would drive me crazy at times.  I remember one night flying feet first through his door in frustration!  The good thing about sound transfer between units, however, is that you can clearly shut it off.  Smoke is something else.  It floats around on the air currents, and the odors embed themselves into the materials of both homes.

I was asked to assist in the amelioration of a project where the neighbors were just short of coming to blows in the form of attorneys.  Two, moderately new, side-by-side condos located on the edge of a golf course.  The smokers live in a two-story end unit.

  • Finished basement with a walk out patio under a deck where a smoker likes to sit and watch the golf course;
  • An attached garage on the front where a smoker occasionally likes to sit with the garage door open;
  • A eating area next to the kitchen next to a sliding door to the outside;
  • A loft and bedroom area on the second floor.

The non-smoker unit next door is a single story with a finished basement.

  • Owner’s study backs up to the sitting area by the kitchen next door;
  • Cathedral ceiling in the master bedrooms mates to the smoker’s unit;
  • Basement bedroom, bathroom and utility area mate to the finished basement next door.

I wanted to get a handle on what causes the pressure differences between the units so I measured the airflows of the bath fans.  Both units have recirculating range hoods.  Both units are heated and cooled with conditioned air systems.  Both units have clothes dryers vented to the outside.

The smokers’ unit has four bathrooms with four fans with a total measured airflow of 153 cfm if they were all running at the same time.  The condos were built attempting meet Energy Star requirements and so the 30 cfm fan in the Master Bath is controlled by a timer to cycle on and off throughout the day.  The non-smokers’ unit has three bathrooms and three fans for a total measured airflow of 121 cfm.

The worst-case pressure difference occurs when both units are completely closed up (winter conditions) and all the exhaust systems are running in the non-smokers’ unit and none are running in the smokers’ unit.  So I set up my manometer to measure the pressure in the smokers’ unit with reference to the pressure in the non-smokers’ unit under worst-case conditions, first running the bath fans, adding the clothes dryer, and finally adding the air handler.  The pressure in the non-smokers’ unit increased to – 2 Pa WRT the smokers’ unit.

In order to determine how much pressure would be required to tip the pressure balance the other way, lowering the pressure in smokers’ unit, I installed the blower door in the smokers unit and increased the flow through it to 275 cfm, when the pressure difference was continuously negative.

To reach that level we could have simply installed a 275 cfm fan running continuously in the smokers’ unit, but I chose a combination approach.  I hardwired the upstairs bath fan in the smokers’ unit to run continuously at 45 cfm and installed a quiet 200 cfm fan in the ceiling of the loft also running continuously.  I also installed an exhaust fan in the ceiling of the garage near where the smoker likes to sit and wired it to a motion detector.

Passive HRV

In the non-smokers’ unit, I installed a passive heat exchanger (an HRV without fans).  I connected the 30 cfm exhaust from the downstairs bath to the exhaust side of the exchanger and installed 140 cfm, in-line supply fan to the intake side.  Although totally unbalanced, the heat exchange is enough to temper the air coming into the non-smokers’ home through the return side of the duct system.  As a further precaution, the condo management folks renewed their efforts to seal any penetrations in the wall between the two units.  Going back to retest the units after the equipment had been installed demonstrated that the pressures were now consistently in the right direction as long as the systems were not defeated and turned off.

The non-smoker, however, swore that he could still smell the smoke.  He stated that the air in his study hurt the back of his throat.  I suggested that what he needed to do was to empty out the small room, have the carpet cleaned or replaced, and thoroughly air the space out.  He was not thrilled with the advice.  Once that odor has embedded itself into the materials no amount of pressure difference and changes of airflow will get rid of it.  And even with the cleaning and airing out, the odors are glued to the occupant’s consciousness and may never go away.  It’s tough to change the pressure differences in a mind!


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