New home HVAC systems


On any job, coordinating with other trades and designing around the perforations they make in the walls can be a challenge.

By Glenn Mellors

Recently, I came across an article titled “77 Things you should Consider when Building a New Home.” I was shocked that the author of the article decided to focus more on closet storage than the heating, cooling, or ventilation systems.

As I read the article, there were seven points on closets and storage, five on bathroom “no-no’s”, seven on what to rough-in outside, and 20 on kitchen conveniences. There were only two on HVAC recommendations, and I quote “plan where furnace vents will go instead of letting the builder decide and consider HEPA filtration for allergy sufferers.” That was it! Everything you need to know about HVAC for your new home.

Yes, I am making light of a very serious situation, but in trying to find information for future new home buyers/builders all I could find was blank pages!

So, why then am I still disappointed when I attend an open house for new homes worth well over one million dollars that have nothing more than a high-efficiency gas furnace, basic entry-level air conditioner and possibly an HRV with short circuit installation mounted to the ductwork? Because we treat anything in the basement like it means nothing and we budget for HVAC in the same fashion.

If we believe that HVAC systems are the lungs and heart of a new home, then we need to stop devaluing it and start educating consumers and builders on the value of a properly selected HVAC system that will increase the comfort, health, and efficiency of the home for many years to come. Our industry may start in the basement, but our work finishes in every single room.

Four critical factors

Let us break it down to simple terms: HVAC equals indoor air quality. But how so? If we break down what makes great indoor air quality, we have four major contributing elements:

  1. Temperature (heating/cooling)
  2. Humidity (lack of or too much)
  3. Airborne particles (filtration)
  4. Volatile organic compounds (purification)

Design considerations when building a home need to make ample room for the equipment necessary to provide the best affordable solution for these four critical areas of indoor air quality. This may mean a mechanical room the size of a small bedroom, preferably isolated from the rest of the home, and not sharing the laundry room! It is important to understand the term ‘HVAC’ before we open the blueprint and start designing the system. Room availability and outdoor wall space will be the number one factor to consider.

Better air to breath

As a bit of a disclaimer, we must consider that there are up to four governing bodies that set standards of acceptance in the area of building codes. First, we have the Canadian Building Code, superseded by the provincial building codes, over-ruled in many cases by municipal building codes, and finally, subdivision variances. So, for us to focus on a specific ruling, you would have a manual that would dwarf the entire Harry Potter series!

Every marketing company focuses on promoting the “highest” or the “most” efficient products made, and for the most part building codes try to accomplish just that. But, when attempting to do this, there are design considerations and changes happening that the average small independent contractor struggles to keep on top of.

It seems ironic to me that we tighten the envelope of a home so much to achieve optimum efficiency that we must go around poking holes to let us breathe. What have we learned? What goes in must come out!

Top-down model

Gone are the days of one hole in the top of our tent to let out the bad air and a door to let in the fresh air! Now, when we look at the plan of a home, we need to look at it from the sky. Imagine the outline of the house as the only means of exhaust and intake. Now, consider everything that needs to penetrate the outline several times for each of the four design considerations. We must share that outline with other trades for their needs as well and each of them needing exhaust and intake opportunities as well!

Here is a list of possible exhaust and intake requirements to consider:

  • Bathroom fans
  • Kitchen exhaust
  • Laundry
  • Water heaters
  • Make-up air
  • Plumbing vents
  • Attic ventilators
  • Fireplaces
  • Foundation vents
  • Windows
  • Electrical
  • Gas meter

I am sure that I have missed a few, but as you can tell by the list, there are several perforations in the building envelope that must co-exist. What do I mean by co-existing? Well, each of these perforations are either an entrance or exit. The improper design will create a short circuit whereas fresh air vents may draw in contaminated air. The byproduct can be contamination of the indoor air, poisonous products of combustion, deterioration of building materials, and in the worst cases, a recipe for causing death.

Co-existence challenges

Codes vary by jurisdiction, so it is important to maintain a good level of communication with local inspectors. Obviously, design criteria must accommodate windows and doors, but here is a much larger list of challenges that must be accommodated as well.

Remember, with new home opportunities, don’t forget that you can vent above windows and doors instead of trying to stay within the foundation of the home. This allows intake to be below the windows and increases available wall space.

Snow depth is a factor and must be considered in design – property lines, and variances, as well as sidewalks and public areas, also play a factor. There needs to be special consideration for direct vented versus power-vented appliances – especially if located on the same side of the home. Make sure radon vents are far enough away from intakes so as not to recirculate contaminated air back into a combustion chamber of another appliance.

Wind and wall choices can affect how air pressure can lock out pressure sensing switches and need to be considered. Plumbing vents both on the roof and at ground level along with storm sewer/eavestrough connections can play a role in location for intakes. Gas meters and regulators, laundry vents, and electrical access are other considerations you must be aware of.

Now you can understand why there are a lot more than just 77 things to consider when building a home.

Fortunately, provinces have courses and certifications for building design practitioners (BCIN in Ontario) and building code identification certifications in western provinces. I highly suggest partnering with a good engineering firm to assist in HVAC design (unless your company is large enough to have certified people on staff). Most of us active in the trades still need to seek assistance.


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