TIPS FOR DESIGNING A MECHANICALLY SENSITIVE HOUSE

Written By Guest User

If you are designing a house and would like to reduce or eliminate bulkheads and corner boxes, ensure large trunks do not have to offsetting under beams or furnace vents terminating at the front of the house, this resource page is for you.  Mechanical systems that are cost effective to install and operate efficiently require a mechanically sensitive framing structure.  This often requires planning your structure in tandem with your mechanicals.  Read on for tips and tricks to designing an award-winning house. 

Mechanical Rooms

  • The location of the mechanical room should be relatively close to the exterior wall to which the combustion appliances will vent.  

  • The venting wall typically requires about 8’ of clearance if vents are horizontally spaced.  

  • Mechanicals rooms or exterior walls reserved for venting should be a min 18” above grade.

  • Mechanical rooms should not have a window as these pose clearance issues to venting terminations. 

  • The TSSA gas code requires the front of a forced air furnace or air handler to have a minimum 32” clearance for servicing.

  • Mechanical rooms need space for the air exchanger too.  It is now a code requirement for all houses to have an Air Exchanger (HRV/ERV).

  • The recommended minimum size for a rectangular mechanical room is approximately 72” in depth and 54” in width.  Alternatively, for a wide and shallow configuration, a dimension of approximately 30” in depth and 84” in width is suggested.  NOTE:  The latter configuration requires a double door, so all appliances are accessible for servicing.

Structure

  • The selection and design of beams in the basement is important.  If your structure is unique, we recommend seeking input from an HVAC professional.

  • Flush beams in basements often pose challenges.  Typically, they create a barrier inside the joists where mechanicals cannot pass.  This forces HVAC, plumbing, and electrical components to roll under, forming an unintended bulkhead.  Moreover, plumbing drains can only slop downhill therefore the flush beam creates a much lower bulkhead than if the beams were dropped.

  • Flush beams in basements can be beneficial if they are strategically designed for spaces where large rectangular trunks and plumbing drains are planned to avoid offsetting under dropped beams.

Multi-Unit Residential (MURBs)

  • The floor/ceiling assemblies between units are fire rated AND require a sound attenuation rating. Therefore, they should not contain any HVAC ducts.  In this case, all ductwork is to be in bulkheads inside the building envelope under the fire rated ceiling of the apartment or condo.

  • In apartments or condos, careful consideration of window height is crucial, especially since there is often a necessity for a perimeter bulkhead.  Please ensure that there is a minimum of 12” from the ceiling to the top of the windows.

  • Since the ceiling is rated and cannot be penetrated, ventilation piping and venting (fans or air exchangers) needs to be strategically located/planned to avoid pipes traversing under the heating trunks, which then creates a double low bulkhead.  

  • Mechanical rooms in MURBS are best located close to an exterior wall that is suitable for venting. 

  • Careful consideration should be given to the location of Mechanical rooms containing equipment that can be a subject to possible explosion (boilers operating at pressure greater that 100 kPa; certain types of refrigerating or transformer equipment) – these rooms are not allowed to be located under required exits or common entrance (as per OBC 9.9.5.8)  

Windows

The price of windows doesn't necessarily indicate the comfort they provide and relying on Energy Rating (ER) can be misleading. While high ER-rated windows are marketed as high-performing, the achieved high ER typically allows more solar heat energy, reducing heating fuel consumption but leading to unforeseen consequences. Not only does a high ER require a larger air conditioner and expanded ductwork, it also causes temperature volatility based on sunlight and orientation.  Further high ER makes rooms in direct sunlight uncomfortably hot in both summer and winter. Conversely, rooms without direct sunlight may experience temperature drops.  In summary, careful consideration of window specification is crucial to avoid discomfort.  We recommend a lower U-Value AND a lower SHGC that is considered minimum code.

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