Updating Market Perceptions of Building Air Tightness and Ventilation

As Canada’s most populous province, Ontario will increase the energy performance level of homes by 15% starting in 2017. The new changes are legislated in the province’s updated building code document known as SB-12. The two biggest changes are complimentary; all new homes require heat recovery on ventilation systems and there are incentives for making buildings more air tight as verified by air leakage testing.

Gone are the days of a principal exhaust-only bath fan as a means for ventilating a house. As of 2017 either a Heat Recovery Ventilator (HRV) or Enthalpic/Energy Recovery Ventilators (ERV) are mandatory. Amen! But are home owner’s ready? What about builders, trades and municipal building inspectors?

Most homeowners don’t know much about their ventilation systems much less how to operate and maintain them. Adding insult to injury, HRVs are poorly understood by building official and builders alike. We commission ventilation systems in custom homes and with surprising regularity what we’re finding in the field is disturbing. If it’s not the homeowner turning the system off due to excessive noise, it’s trades people botching the installation and the municipal inspectors failing to catch installation errors. The industry is poised for a collision due in large part by lack of education.

Is Your Tight Home a Cesspool of Mould, Mildew and Rot?

The 1980s launch of Canada’s avant-garde R2000 program for high performance homes never took off. Though tens of thousands of R2000 homes were built, wide-scale adoption never took hold largely due to resistance from the home builders association in the early days.

The standard called for air tight homes with heat recovery ventilators not to mention limited carpeting for better indoor air quality. Some 30 years on, there’s a lot of conjecture about these high performance houses and why they weren’t more popular; and the most damaging, ironic allegation is that they had bad indoor air quality.

Even celebrity renovators like Mike Holms, is on record in Canada’s national newspaper spewing hyperbole like “I remember stories of test homes built so tight, the windows would break if someone slammed the front door. The windows were tiny, and you could literally suffocate in the houses if there was no heat exchanger.” This last sentence shows a persistent conflation of windows and ventilation and this notion needs to be dispelled; windows are for connection to the outside world, day light and fire egress, not for reliable ventilation of conditioned living space. Keeping in mind that all these homes had HRVs in them, Holmes egregiously adds “What they didn’t realize then was that tight houses were also prone to rot. If homes don’t let in some air, they also don’t let moisture out, and that moisture gets inside the walls and eats away at the structure. Your nice, tight home becomes a cesspool of mould, mildew and rot. Houses have to breathe.” I’m sure Homes would take back many of the above statements, but the stigma persists for air tight houses. It doesn’t take much for home owners to get the jitters and it would only take a few ignorant people to suffer health related illness because they unplugged their mechanical ventilation system or because it was improperly installed.

Homes Need to Dry, Not Breath

Homes need greater energy efficiency and the lowest hanging fruit in terms of savings is air tightness. We’re also adding more envelope insulation and the high R-value assemblies mean that if conditioned indoor air sneaks through cracks in the envelope, the moisture the air carries will condense inside the colder assembly. So it’s crucial that high R-value assemblies are more air tight for the sake of durability.

Prior to this code change, mechanical ventilation systems in Ontario largely consisted of crude and wasteful exhaust only ventilation systems. These bath exhaust fans would grind away in the background forcing air out of the house, typically through one large principal bath exhaust fan which would pull fresh air indiscriminately through building envelope leaks. But as we add heat recovery to mechanical ventilation systems, the energy of the exhaust air will be retained in the living space.

 Pulling the Plug on Loud

In my years of energy auditing, there’s a direct relationship between noise and machine use. The more noise a machine makes, the less likely occupants are to use said machine, even if their health depends on it. In the last year alone, I visited 2 homes where the HRV was unplugged by the home owner because it made too much noise or caused a draft they “didn’t like”. Loud kitchen exhaust ranges over gas stoves in homes tend not to be used and ditto loud bath fans; even if the mould on the wet window frames is screaming for fresh air.

The irony is that homes are getting more quiet indoors as they become more air tight and better insulated. These significantly quieter new homes tend to make small noises from mechanical equipment sound louder. As a designer, if you’re thinking of builder-grade HRVs be forewarned; the system may be get unplugged and the home owner will suffer if its noisy.

In a 3 month span, I found two homes in the municipality of Toronto, each less than 1km from the Humber River, that had disastrously installed HRVs (See photos below). Both systems were permitted by the municipality and it’s reasonable to infer that both systems were inspected and given the green light by the municipality. For the record, it’s not just domestic HRVs, even the expensive European systems are subject to botched installations (see photos below).

 Conclusion

The province would be wise to push ventilation system literacy onto homeowners so they don’t accidentally pollute the air they breathe. Further, the province would be wise to train building inspectors, designers and HVAC technicians on what to look for in a properly installed HRV. A bit of training on why it’s preferable to have low sone ratings on ventilation equipment and why fully ducted systems are preferable to “Simplified Installation” would be helpful.

As for the mechanical designer of the home or the mechanical system, you’ll be mandated to have heat recovery so make the house air tight to ensure the HRV earns its keep. You can size a smaller heating plant using actual air leakge rates in CAN/CSA-F280. Further, consider having these “lungs of the house” commissioned not only to catch issues in this budding industry but also tune the systems so that each room gets the designed quantity of fresh air that the occupants deserve.

 

 West of the Humber

Note that the intake and exhaust pipes should be as short as possible; most HRVs don’t provide enough static pressure to overcome long distances so we try to make the pipe connections to the outside as short, direct and large diameter as possible to encourage maximum air flow. Note also that the fresh air intake duct needs to be completely insulated, but it doesn’t hurt to insulate both pipes if the system doesn’t run continuously. All transverse and longitudinal seams should be air sealed before you insulate the pipe. Typically, the diameters of pipe are 6″-8″ and the lengths of pipe are no more than 12′ if using a smooth walled pipe. If using corrugated or flex duct which adds twice the air flow resistance, the total installed length should be halved. Here’s a perfect example of what to avoid where the intake is about 40′ in measured length and the exhaust is about 60′. The effective length are effectively 55′ and 80′ respectively, forget the fact that the diameter is reduced to 4″ :

East of the Humber