Air Leakage – A Health and Safety Concern

Today I was up in The Villages in Florida. For those that are not familiar with the area, The Villages is a retirement community, spanning across three counties in North Central Florida. It is for the most part ranch style, cookie cutter houses that are spaced close together, but tastefully done, and offer the homeowners a real sense of community and companionship as they continue through their retirement years. The reason I was in The Villages today was so that I could do a blower door test and a duct leakage test for some family friends that had recently moved up there from the Clearwater, Florida area.

A Blower Door Test is designed to test the tightness of the house. We are looking to find out how much air is leaking into and out of the conditioned spaces of the structure. The greater the leakage, the more conditioned (cooled and heated) air will flow through cracks, crevices, and other openings in the walls and ceilings, thus raising the energy bills and also decreasing indoor air quality. More about that in a minute. Florida energy code says that new and retrofitted construction must be tested by an independent third party and must be within 3-7 air changes an hour. By air changes per hour we mean how many times per hour 100% of the indoor air will be replaced with the outside air. The greater the temperature difference between the inside and the outside the faster the air will flow naturally.

Three to seven air changes an hour in new construction is a rather large range. In my opinion you want to be as close to three exchanges per hour as possible. Any more than that you are wasting money as your heating and cooling dollars are leaking out to fast. Much less than that you take a risk of not having enough fresh air coming into your house for proper ventilation and indoor air quality control. Houses do need to breath.  However, if the exchange rate is much under three I consider it better as then I can control adding additional air through the HVAC system and filter it as we bring it in.

So, let’s back up to the house that I looked at today. It is a ranch style house with vaulted ceilings, all ductwork for the heating and cooling system is in the attic, with return grills throughout the house. The windows are all relatively new and just recently the doors to the outside have been upgraded. The kitchen just went through a remodel. The Air Conditioning coil was replaced at the time the house was purchased and the ductwork around the furnace was sealed.

The first test I normally do is the blower door test. The reason I do this test first is that it gives me an idea of the overall tightness of the building and from there I can determine what I am looking at with the duct testing  that comes second. After making sure all windows and doors in the house were closed I setup my test equipment and ran the automated test sequence that tests the leakage at different pressures to come up with a true leakage rate.  In this case the house was leaking within legal requirements for new construction at 5.08 air changes per hour. What this means is that 100% of the indoor conditioned air is being replaced by outdoor air about every 12 minutes. Think about that for a minute. All of your conditioned air, the air that you have paid to heat, cool, dehumidify is being replaced by unconditioned air every 12 minutes. More if the wind is blowing and causing greater pressure differentials between inside and outside.

Once the automated test sequence is complete and I have a chance to look at the results I like to turn the blower back on and depressurize the house (put the house pressure lower than the outdoor air pressure) and go around and find the leaks. This is really easy to do as you can feel the air being sucked in at any point were there is a leak. Under normal conditions I find that most of the leaks are on outside walls, around windows, doors, and around electrical outlets. In this case yes, the electrical outlets and the switches were a concern, but what I found next was a bigger problem. The outlets, door frames, switches, and even the door latch cutouts on the indoor walls (those walls dividing rooms and not on an outside wall) were just gushing air into the building. Several of them had really high flows that you could feel standing pretty far away from the wall.

Why is this a concern? First, the air that is being sucked through wall cavities is not clean. This air usually enters the wall cavity through the attic and then is sucked down between the sheet rock and through air gaps around outlets. It picks up any dust, mold spores, and other contaminants that are in the wall or the attic insulation. This can lead to several health concerns. If that is not enough there is a bigger problem, and this is a pretty major safety concern. In order to understand this we need to look at how an interior wall is supposed to be constructed.

When an interior wall is built there is a header stud that is run across the top at ceiling level. Then a floor stud is laid down and nailed to the concrete pad (or floor). Then, 2×4’s or 2×6’s are put between the two at 16 inch to center spacing. Once this framing is done, sheet rock is screwed to each side effectively sealing each 16 inch cavity into an air tight (or close to air tight) space. That’s in a perfect world. The reality is that we also need to have electrical and sometimes water lines and vent pipes run up the wall cavities to the attic. In most ranch style construction the electrical lines are run across the attic floor and holes are drilled from the attic into wall cavities, the wires are dropped into the cavities and then distributed around the perimeter of the rooms for outlets and switches.  These pathways allow for air movement between the cavities and between the cavities and the attic.

This is a good time to talk about fire safety and smoke control. If a fire starts in one of the wall cavities, or in the attic, or in one room in the house the fire and smoke will spread through any opening in a wall cavity. If I can feel air movement between the walls, the attic, and the conditioned space fire will easily be able to spread through these spaces as well. Why is this allowed to happen? Well, according the the building codes it is not. What is supposed to be done is that any penetration by wiring, water pipes, or ductwork between the attic and the wall cavities is supposed to be sealed with a fire proof caulking. Any gaps that are left in the building process are also supposed to be sealed. This has been the code since the early 1970’s.

Back to today’s house. I found significant air movement between the attic, the wall cavities, and the conditioned space. So, what I found was a health, safety, and energy cost issue. All most likely caused by improper installation of caulking during the building process. Why is this a concern in a retirement community where the houses are built very close together? Because most fires involving senior citizens involve fatalities. The houses being so close together also allows fire to spread very quickly. This was before I tested the ductwork.

Even though I found an air exchange that was within legal limits for Florida I wanted to quantify how much of the leakage was in the ductwork. In order to do that I needed to run a second test to specifically test the ductwork, by itself. The first step in this process is to seal every supply register and return grill with a sticky adhesive cover.  It is very important for this test to make sure that the ductwork is isolated. Next we connect the blower to the return grill and seal the connection. Then I turn the blower on and depressurize the ductwork to 50 pascals (or a .1 inch Water Column). There is a reason for this number. Most air conditioning and heating systems are designed to run at a .1 inch Water Column (a fraction of a PSI) and this lets us measure the leakage with a known quantity of air. Once the pressure stabilized I was having to continuously move 184 CFM (Cubic Feet Per Minute) of air.

Let’s put this into perspective. Every air conditioning system needs 400CFM of air per ton (12,000 BTU/hr) to operate properly. In this house the air conditioning system was a two ton unit, this needing 800 CFM of air to cool and dehumidify the house properly. If the ductwork is loosing close to 200CFM of air it means that 25% of the air in the system is either being sucked into the return duct or leaking out of the supply duct through leaks in the attic. 25% of the customers cooling and heating dollars are leaking out of the building, or the system is having to work 25% harder to cool, heat, and dehumidify air that is in the unconditioned space. Additionally if there is air being brought into the return duct part of the system from the dirty environment of the attic there may be some health concerns as well having to do with dust, insulation, and possibly mildew, mold spores, and insect/bird/animal feces. Personally this is not something I would want to breath in.

Upon completion of my testing I was able to give the customer a report showing the leakage rates and I was able to walk them around the house showing exactly where the air was coming from. I also recommended that they hire someone to come in and seal any openings to the wall cavities from the attic and also seal the ductwork connections to the registers and grills in the HVAC (Heating, Ventilation, and Air Conditioning) system. Once this is done they will have a safer, more comfortable, and more energy efficient home.