The Village Green

A blog about how Canadians can achieve energy independence by powering down and then powering up the right way.

It's a couple of days before Christmas, i'm sitting here with a cheap bottle of Chilean red, there's about an hour of sunlight left in the day and CBC Radio says it's going down to minus 13 tonight. What a great time to riff about the most boring topic in the world which one day you'll be glad you actually know something about.  

Most HVAC equipment is too big
According to the Canada Mortgage and Housing Corporation, most Canadian homes have furnaces far larger than required.  Similarly, studies in the US have found that the majority of contractors size equipment inappropriately, generally recommending equipment that is larger - often much larger - than necessary.  As you work to turn your house into a high-performance home, it’s critical that the systems you choose be sized properly.  

When it comes time to replace their furnace or air conditioner, most people call contractors they find in the phone book, on the internet or who have been recommended by friends.  They get free estimates and choose the one they like the best.  This is a problem because one of the laws of economics is that you will eventually get what you pay for: free estimates can end up costing you a lot of money.  

Rules of thumb 

Most contractors size HVAC equipment using rules of thumb.  Thumbs are good for many things but they’re not good for sizing sophisticated equipment.  By guessing at the size of the equipment they should be installing, contractors have tended to over-compensate by installing systems larger than necessary.  Oversized furnaces and air conditioners can create problems such as the following:  

  • We end up paying for capacity we don’t need 

  • Over-sized equipment never gets to run at peak efficiency.  We want furnaces to run hot.  By combusting fuel completely, they attain their performance levels.  Further, a furnace running in short bursts uses more energy, just like a car in city driving conditions compared to highway conditions.  Also, oversized heating equipment can cause large and uncomfortable heat swings in a home.  The two issues here are comfort and increased operating costs.  

  • Similarly, over-sized air conditioners often don’t run long enough to properly de-humidify air which can result in comfort issues or mould growth. 

  • Because they don’t get to run at the levels they are designed for, oversized equipment can break down more frequently and have shorter life-spans.

Most homes built prior to the 1970’s have little insulation and, in some cases, none at all.  Over time, homeowners tend to make efficiency improvements: new windows are better than the old ones they replace; seals on doors get better; batts of insulation are added in the attic; weather stripping and caulking gets added.  Some homeowners will make these improvements.  Others won’t.  Two otherwise identical houses, side-by-side, could have drastically different performance and heat loss ratings.  

Over time, the improvements we make or don’t make dramatically affect the efficiency of a home.  As we look at the heating and cooling needs of a house, we have to look at every house as unique and as a whole system.  Rules of thumb don’t work.  

Eliminating the guesswork: getting a heat loss / heat gain calculation 

There are recognized standards for determining the heating and cooling needs of your home and eliminating the guesswork.  In Canada, recognized standards for determining heat loss include the Canadian Standards Association’s (CAN/CSA F280-M90) and procedures by the Heating, Refrigeration and Air Conditioning Institute (HRAI).  Most evaluators now will also have software packages that enable them to develop heat loss models.  Also, if you get a Natural Resources Canada (NRCAN) ecoENERGY audit done for your home, the software used in the process will meet the intent of this standard according to NRCAN. 

The heat loss for your house will be impacted by variables such as : 

  • The local climate 

  • The size, shape and the orientation of your home (i.e. what direction it points to) 

  • Insulation levels 

  • The air tightness of your home which affects how frequently the air in your home is being lost and replaced 

  • The quality of your doors and windows (and their placement)

  • The number of people in your home (people give off a lot of energy)

  • Lighting and appliances (which also give off a lot of heat)

A proper heat loss exercise will create a working model of your home which accounts for these variables.  A proper sizing exercise for your home will cost you around $200 - $300.  Your local municipality or utility might have rebates to help offset this cost.  It’s money well spent because it eliminates the guess-work. 

Getting quotes from contractors 

Using a rule of thumb to get a directional or initial sizing is fine but you don’t want to use this as the basis for you final system sizing.   You will want your contractor to do a final sizing exercise prior to installing they equipment they recommend.

If you’re choosing a contractor who’s given you an estimate, you’ll want the contractor to agree in writing that they will provide you with their calculations, assumptions, processes, a print out of their computer modeling or worksheets and they standards adhered to in conducting their analysis.  

This will be your guarantee that the work was done the right way.  

Gabriel Draven 

Village Technologies