Blower Door Test Guide for Ontario Houses: What It Is, What It Costs, ACH50 Benchmarks by Age of House, and What the Number Tells You to Fix

What the test actually does

The technician sets a frame with a nylon panel and a calibrated fan in an exterior doorway, closes every window and door, opens the interior doors, shuts off the furnace and the fans, and runs the fan to pull the house down to 50 pascals below the outdoors. Fifty pascals is about the pressure of a 30 km/h wind on every wall and the ceiling at once, which is why the test is repeatable in July and January. The gauge reads how many cubic feet per minute the fan is moving to hold that pressure: CFM50. Every one of those cubic feet is coming in through a hole somewhere.

To turn CFM50 into something you can compare between houses, multiply by 60 and divide by the volume of the house in cubic feet, basement included. A 2,000 sq ft two-storey with 8 ft ceilings and a 1,000 sq ft basement is about 24,000 cubic feet. If the fan reads 2,000 CFM50, that is 2,000 x 60 / 24,000, which is 5 ACH50: at 50 pascals the whole air volume of the house is being replaced five times an hour. Under normal weather a house leaks at roughly a twentieth of that, so 5 ACH50 is about a quarter of an air change an hour on an average day, and more on a windy one.

The Ontario benchmarks

A technician will also give you the equivalent leakage area, the size of the single hole that would leak the same amount. On a 1980s house at 8 ACH50 it is about the area of a basement window, open all winter. That is the figure to say out loud when somebody tells you the house is fine.

What it costs and who does it

A standalone blower door test from an energy advisor or an air sealing contractor who owns the rig runs $300 to $450 in Ontario, before HST, and includes the walk-through with the smoke pencil while the fan is running. That walk-through is most of the value; the number tells you how much, the smoke tells you where. Ask for the CFM50 and the house volume on paper, not just the ACH50, so the next test can be compared to it.

The test is also built into an EnerGuide home evaluation, $500 to $800, done by a registered energy advisor. That is the only version that counts for the assessment path of the Home Renovation Savings program, and the program wants one before and one after, with pre-approval between them. If you are doing a bundled insulation job and want the rebate, do not pay for a standalone test and then pay again for the evaluation; the home energy audit page lays out the sequence and the rebate page has the amounts and the conditions.

On a new house, the test is part of the SB-12 compliance when the builder takes the air-tightness credit, and it is done at or near completion by an advisor the builder hires. If your builder has promised a tight house, ask whether the test is in the contract and what number is promised. “Tight” is not a number.

What the number tells you to fix

1. Over 8: the attic plane and the rim joist are the whole story. Nothing on the windows matters yet. The attic section and the rim joist page are where the first $2,000 goes, and the test afterward will usually show 5 or 6.
2. 5 to 8: the big holes are done or were never there. Now it is the hatch, the pot lights, the plumbing stack, the chimney chase, the electrical boxes on exterior walls and the garage-to-house door. The smoke pencil finds them one at a time.
3. 3 to 5: a good existing house. The remaining leakage is mostly in the walls and around the windows, and chasing it costs more than it saves unless the siding or the drywall is coming off anyway. Spend the next dollar on the attic R-value or the furnace.
4. Under 3: stop sealing and start ventilating. At this point the bath fans, the range hood and an HRV are the way air moves, and a natural-draft water heater or fireplace can backdraft. What to check.

The number also changes the heat-loss calculation. Air leakage is one of the inputs in a stamped heat-loss design, and a house that went from 9 to 4 ACH50 needs a smaller furnace or heat pump than the one the old number would size. OntarioHeatLoss.ca does that design from the tested number, and it is where the HRV size for a new house comes from as well.

Where the test goes wrong

A test with a window cracked, a fireplace damper open or the dryer vent flapper stuck is not a test; the advisor is supposed to walk the house first, and you can watch. A test on a very windy day is noisy and a good advisor will say so. A test on a new house before the drywall is finished reads worse than the finished house will, which is the point of doing one then: it is the last day the holes are reachable. I have the crew do a rough test on every ICF house with the ceiling poly up and the windows in, and the second number at completion is always the better one.

The thing a blower door cannot do is tell you where the heat goes by conduction. A house at 2 ACH50 with R-12 in the attic is a tight cold house; the attic R-value rule is the other half, and the SB-12 page explains how the code trades the two against each other.

Questions people ask

Sources and further reading

• EnerGuide home evaluations: Natural Resources Canada: what a registered energy advisor does, the blower door test and the rating that the assessment-path rebates depend on.
• Ontario’s Building Code, Supplementary Standard SB-12: the energy-efficiency packages that set the R-values for attics, walls, basements and slabs in a new or renovated Ontario house.
• Keeping the Heat In: Natural Resources Canada: the plain-language Canadian guide to air sealing, insulation materials, basements, walls and ventilation.