John Ellis on the Flow Lab Podcast

Six Principles for Designing Healthy Indoor Environments

 

In a recent Flow Lab episode we sat down with John Ellis, an indoor environmental consultant who works with some of the most sensitive clients you can imagine. Think cystic fibrosis, oncology patients, lung transplant recipients, and severe asthma. For those people, the way we design and run HVAC systems is not a nice to have. It is a medical decision.

When John talks about indoor air quality, he does not start with gadgets. He starts with six basic principles that every contractor should be thinking about on every job, long before anyone talks about UV lights or magic boxes.

He frames them like this:

  • Thermal comfort

  • Ventilation

  • Filtration

  • Humidity control

  • Pressures and infiltration

  • Pollutant identification and source control

This is not a checklist you work through once. It is a way to look at every building you touch.

Below is how each principle plays out in the real world, and how you can put them to work in your own projects.


1. Thermal comfort is a health issue

We tell homeowners we are in the comfort business all the time. John means that literally. Comfort is not just a number on the thermostat. For compromised people, small shifts in temperature or drafts can change how they feel from minute to minute.

He works with clients who can walk into a building and feel pressure and temperature imbalances in their bodies. Their lungs and sinuses are the test instruments. Loose envelope details, badly balanced systems, or hot and cold spots are more than nuisances for them. They are triggers.

For contractors, that should be a cue to take comfort complaints more seriously than, “you might need a bigger unit.” It might mean checking temperature stratification between rooms and floors, looking at how supply and return locations interact, and measuring room by room airflow instead of assuming it is fine.

If you do building performance work, this is where good diagnostic tools let you move from guesswork to numbers. You can show a client that their cold bedroom is running lower flow and lower temperature than the rest of the house, and you can build a plan from there.


2. Put the “V” back in HVAC

John likes to say that the why never changes, just the how. The reason we ventilate is always the same. People need fresh air and controlled dilution of indoor pollutants. The way we ventilate in Arizona should look very different from how we ventilate in Florida or Minnesota.

Good ventilation design covers two main things. You need to dilute and control indoor pollutants and you need to manage building pressures, especially in tight homes and commercial buildings. Sometimes that means accepting an energy penalty. John will gladly take a few extra kilowatt hours if it keeps a medically sensitive client out of the hospital. If you can hold a tight home slightly positive and keep the bad stuff from being sucked in, that tradeoff is worth it.

From a building science perspective, ventilation has to live in harmony with the envelope and with exhaust devices. You cannot just add fresh air and hope the rest takes care of itself. You need to know how the space behaves when fans are on, when doors are closed, and when the weather shifts.


3. Filtration that is designed, not just installed

“Every piece of equipment we walk up to has some type of filter in it.” John said that almost in passing, but it is a big deal. Filters are everywhere, yet a lot of systems treat them as an afterthought.

Good filtration design does two jobs at once. It protects and keeps the equipment clean and it cleans the air in the space in a predictable way. That means thinking about bypass around the filter rack, filter surface area versus system airflow, and pressure drop at real CFM, not just at a lab test point.

In the episode John mentioned his work on a high performance filter system as an example of taking filtration seriously. The idea is to use a cabinet with enough real estate and the right geometry so you can get high MERV performance without killing the static pressure. That specific product may not be the right fit for every job, but the design thinking behind it should be.

The takeaway is simple. Do not just upgrade the filter. Design it.


4. Humidity control in both directions

Humidity is not just a southern problem. John described typical northern setups where homes need humidification in winter, dehumidification in summer, and balanced ventilation all year long.

Too much humidity and you are dealing with mold, dust mites, and comfort issues. Too little and you see dry skin, nosebleeds, irritated airways, and static shocks. If you work with sensitive clients, those symptoms matter.

Your job is to decide what the target indoor relative humidity range should be for this client and climate and what combination of dehumidification, humidification, and ventilation will hold that range most of the year. You also need to think about how quickly the house responds when the weather swings.

All of this lives inside the larger building picture. Tightening the envelope often makes humidity control easier because you are not constantly fighting outdoor air that sneaks in through random cracks. A leaky envelope drags in air at whatever temperature and moisture level the weather decides, and your equipment has to chase it.


5. Pressures and infiltration

This is where John really starts to geek out.

On a diagnostic project, he will baseline the house, map pressures, map moisture, and map temperature. He looks for stratification and what happens to that stratification when heating or cooling comes on. He finds the neutral pressure plane and watches how it rises or falls when exhaust fans run or leaky ducts start pulling on the building.

If the neutral pressure plane climbs up, he focuses on the upper parts of the house. If it drops, he looks down low. Stack effect, wind, and mechanical systems all play a role, and mechanical often dominates, especially when ducts are outside the envelope.

Infiltration is a huge part of this story. Too many people plug default numbers into their load calculations and call it a day. With today’s tools we can do better. You can measure whole building leakage, see which side of the envelope is getting punished by pressure, and decide whether you want that leakage or not.

When you understand how pressures and infiltration are behaving, everything else becomes clearer. Comfort complaints make more sense. Moisture problems make more sense. You can stop guessing and start designing.


6. Pollutant identification and source control

The last principle might be the most important.

John repeats “source control” in his classes like a drumbeat. If you can identify a pollutant, you can start asking where it comes from. Sometimes it is outdoor air that is finding its way in. Sometimes it is products or furnishings that were brought into the space. Sometimes it is materials the space was built or renovated with.

Only then does it make sense to talk about filtration, ventilation, or remediation. Otherwise you risk treating symptoms while the cause keeps running in the background.

John sums the mindset up simply. Keep it dry. Keep it clean. Keep it ventilated. Keep it thermally comfortable. Keep pressures in line. Those ideas connect every principle together. Moisture control supports source control. Better filtration and pressure control make ventilation more effective. Tightening the envelope helps comfort and humidity control at the same time.

For a contractor or consultant, this is where your building diagnostics meet your indoor air quality work. Your testing tools help you chase down the pathways. Your design and product choices handle the fix.


Bringing it all together

The big thing we took from John Ellis is that indoor air quality is not a product category. It is a way of looking at the whole indoor environment.

If you start from these six principles

  • Comfort

  • Ventilation

  • Filtration

  • Humidity

  • Pressures and infiltration

  • Source control

you will naturally move away from magic box thinking and toward whole system solutions.

You will also have a clearer way to talk to clients. Instead of leading with a device, you can lead with a story about how their building behaves and how you plan to change that behavior. That is where good building science, solid diagnostics, and thoughtful product choices all pull in the same direction.

And if you want your team to hear these ideas straight from John, you can always send them to the full Flow Lab episode and start a conversation about how to bake these six principles into every project you touch.

Want to hear the full story?

Listen to our conversation with John Ellis on The Flow Lab Podcast – now streaming wherever you get your podcasts.

Flow Lab Podcast

  

 

The Flow Lab Podcast by Retrotec

Retrotec has launched The Flow Lab podcast to connect you with the leading minds within the building science industry.  We interview everyone from long-time experts to the newest innovators, exploring the latest technology advancements and industry news. Subscribe on the Retrotec YouTube channel and wherever you listen to podcasts. Like and subscribe to become part of the Flow Lab community!