Vetting ventilation

Using all that water to clean the basement concrete floor in preparation for the floor finish produced a lot of humidity. It was a pointed reminder that ventilation in a more or less airtight space is critical – and that I have to get on with it.

I have been looking into the ventilation issue for more than a year. Yep, this has procrastination written all over it. Because this was clearly not my area of expertise, it took a lot of time to research and time to acquire a basic level of knowledge. I found it difficult to make decisions.

I purchased a very helpful Ventilation Guide by the Building Science Press. This little book gave me an understanding of the basics and an insight into what systems are out there and also got me familiar with the terminology.

The quest into our ventilation options continued at our design workshop. Here we determined that we need a balanced whole house ventilation system powered by an Energy Recovery Ventilator (ERV). The system is called balanced because the fresh air supplied equals the amount of stale air that gets exhausted from the building.

Since then I had help from our mechanical engineer, but still had a wide range of field adjustments and decisions ahead of me.

The basement is divided into two ventilation zones:

  1. The living area of the garden unit towards the front, and
  2. The storage and common areas towards the back of the basement.

One of the first steps was to decide where to place the supplies and returns.

  • Supply: point where fresh air is supplied from the duct work into the building, typically through a ceiling diffuser.
  • Return: point where stale air is pulled back into the duct work and exhausted from the building.

From what I learned through my research, I understood that the returns should be located in the wet rooms. This would be the bathroom and laundry room in the basement.

Placing the returns in the wet rooms eliminates the need for a single point exhaust such as a typical bathroom fan. The ventilation system with the ERV basically becomes the bathroom fan. It also eliminates the energy loss associated with a single point exhaust fan, as this unit has no built-in heat recovery.

I now want to place the supplies so that I get the best possible air distribution and mixing across the basement unit.


For the garden unit, which is undivided with the exception of the bathroom, I place the supply as far away as possible from the return in the bathroom.


To make sure we have sufficient airflow capacity from the living space into the bathroom, I installed an ‘In-Door Pressure Balancer’ at the bottom of the bathroom door.


This little but nifty gadget easily accommodates an airflow of 75 cubic feet per minute (cfm), but reduces noise or light transmission through the built-in louvers.

The back of the basement with the storage and common areas was a little more involved.

I placed the supply into the storage room that also accommodates the ERV. With the help of more In-Door Pressure Balancers, I get the air flowing into the corridor and on into the next storage room. From here I have a duct connection to the utility room.


Air will flow from the utility room into the workshop through another through-the-wall duct connection, and from the workshop into the laundry room through another In-Door Pressure Balancer. Now the air has to flow across the laundry room towards the return.

This may appear convoluted, but we get effective airflow through all rooms with the minimum amount of duct work.

And it was the duct work that kept me scratching my head for the longest time, in particular the duct sizing.

Our mechanical engineer had sized the ducts, but I still felt that I needed some insight into this process.

Mariusz, our plumbing and heating contractor, came to the rescue again. He dropped off an air duct calculator, which is a sliding ruler that lets me look up duct sizes at a given flow in cubic feet per minute and friction.


This gadget increased my confidence while installing the duct runs from and to the ERV location, with one exception. And that was the exhaust duct from the building.

This deserves a blog post on its own, so stay tuned.

About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

2 thoughts on “Vetting ventilation

  1. Is there any particular reason why you chose not to install the duct work before the basement was finished? Seems like that would have limited the eye sores, without significantly increasing cost or diminishing efficiency.

  2. I was simply unfamiliar with the process. Actually, some of the ducts were installed before the basement was finished, others were connected later. I know understand that installing the duct work way before a space is finished will assure good system efficiency and probably save some cost.

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