Blower door test – after insulation

It was time to face the music – or better, the roar of the blower door fan.

Quick recap: We applied for an insulation rebate. To qualify for the rebate, we were required to demonstrate an energy savings of at least 30%. The energy savings are in part calculated on how leaky or air tight a building is.

John, from Chicago Home Performance, conducted a blower door test prior to any insulation and air sealing. That pre-improvement test is used as the baseline to calculate the energy savings. It turned out that our 2nd floor was pretty drafty at 4,763 cfm50 or 13.9 ach50.

The preparations

A lot of work has been completed since that first test:

Were we done with all the air sealing tasks? No – not yet. I still needed to install an insulated back door from the kitchen to the porch and replace the remaining double hung windows with new insulated glazing units (IGU’s).

But – with the insulation rebate deadline approaching, these items just had to wait. We needed to get the post-improvement blower door test done – quickly!

The test

John set up his blower door equipment, just like he did for the pre-improvement test. He fired up the fan – and he didn’t get a reading at first!

The blower door fan has two flow rings (A and B) and a lid that covers the center.


The building was so leaky during the pre-improvement test that John had all of the flow rings on the fan removed.


Fast forward to post-improvements: We had tightened up the building so much that, with all flow rings removed, there wasn’t enough airflow velocity through the fan to yield a valid reading. John increased the velocity by constricting the airflow with the flow ring A, and eventually with the flow ring B.


That finally gave us a valid reading:

720 cubic feet per minute at 50 pascal (720 cfm50) or 2.1 air exchanges at 50 pascal (2.1 ach50).

That is an 85% reduction compared to the 4,763 cfm50 or 13.9 ach50 of the pre-improvement test.

Needless to say that our air sealing and insulation work paid off. We were all surprised – pleasantly surprised!

The meaning of…

What does 85% reduction in air leakage or 2.1 ach50 mean? It would be more than enough to meet the energy rebate requirement of 30% energy savings. But how does it compare to other projects or standards?

The recently published International Energy Conservation Code (IECC 2012) requires buildings to meet 3 ach50 for climate zone 5 (Chicago is in climate zone 5).

The Canadian R-2000 program mandates 1.5 ach50, while the Passive House standard requires 0.6 ach50. The latter is a hard one to achieve, even in new construction.

The Green Building Advisor blog post “Blower Door Basics” by Martin Holladay mentions that “a 2002 study of 24 new Wisconsin homes showed a median air leakage of 3.9 ach50” and “new home builders in Minnesota routinely achieve 2.5 ach50.”

Mind you, these are results for new construction. Tightening up an existing building is considered to be notoriously more difficult. So I think we are doing pretty well with our 2.1 ach50 – although I would like to get it down to 1.5 ach50.

Maybe we will get there once we install the drywall, tape and mud it, once the new kitchen back door is in, and once we have all the new replacement windows installed.

To learn more about blower door tests, read the following: – Blower Door Basics – Blower door

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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.

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