But we know from experience that certain construction features are much leakier than others. The knee walls in the bonus room over a garage or in houses with an upstairs half-story are notoriously leaky.

Interior soffits over bathtubs or kitchen cabinets are also common leak spots. That means the chase that hides plumbing, a chimney, or duct work between floors may have poor seals where it reaches into the attic or down into a crawl space.

In a scenario where a house kitchen sits over a crawl space, while the rest of the structure is over a conditioned basement might mean that kitchen is always too cold in the winter.

Screening for Leaky Ducts

Another important way blower doors can help diagnose the house is by screening for leaky ducts. Whenever the ducts are in a vented attic or crawl space, you can use a blower door to screen for and even estimate the locations of large leaks using the pressure pan method.

Here is how that works: Once you install the blower door and turn it on, with the HVAC system off, place a pressure pan over each supply grille to measure a pressure for a few seconds. If the pressure you measure is more than 1 or 2 pascals, that indicates a large duct leak to the outside is near the supply grille you are testing.

Your Defense Team – a Blower Door

Sometimes it is important to know if the building envelope was built properly in the first place. This could especially be true in new construction. We all know that when the proud owner of a brand-new home is uncomfortable, the HVAC contractor is much more likely to be blamed than the insulation and air sealing contractor.

Being able to run a blower door test and demonstrate that the house wasn’t built according to the details used for the load calculation could help ensure you don’t end up paying the bill for another contractor’s mistake.

The same thing can be applied to system equipment swap outs. Some customers may have unrealistic expectations of new HVAC equipment. They may expect the new equipment to fix pre-existing problems in the duct work or in the building envelope.

The difficult conversation with an unhappy customer will usually go much more smoothly if the HVAC company offers to do some testing and diagnosis of the house and ducts. Do this even if the customer originally declined those services.

If the customer understood at the outset that you can’t make any guarantees if you don’t know how much the ducts and house leak, it will be much easier for them to accept that the problem was truly outside of your control.

Once you move past that conversation you will be in a better position to add a duct renovation or envelope improvements at a later date.

How to Fix the House

By now you may be wondering who’s going to fix the problems that get diagnosed with a blower door. Do we expect HVAC companies to invest in training and equipment to start air sealing attics and blowing in new insulation? In most cases that doesn’t make much business sense, although larger companies might consider it.

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