Ventilation Design for Healthy Indoor Air!

Did you know the indoor air quality of your home can be 70 times worse than the air outside?  When it comes to improving your indoor air quality, it’s a four step process:

  1. Seal your home up as tight as you can (our energy codes are making sure we do this).
  2. Remove indoor pollutants (anything that off gasses – Volatile Organic Compounds (VOCs), formaldehyde, harsh cleaning solutions, etc.).
  3. Dilute remaining indoor air contaminants/gases with ventilation.
  4. Filter out particulates (dust, dander and other) with a Merv 13 filter or higher.

Even though ventilation systems have been required by the IECC code since 2012, many of the high performance homes built today still lack proper ventilation.  Priority Energy has been designing and installing cost-effective ventilation systems for new and existing homes across the United States for over a decade. We have also influenced and helped write state requirements for ventilation for healthier living spaces.

Our buildings do not need to breath, but the people in them do. For healthy indoor air our buildings need mechanical ventilation. More specifically, they need whole building mechanical ventilaton systems.  

To understand what this means, let's start with what it doesn't mean:

  1. This is not the ventilation installed in your attic (soffit, mushroom, gable, and ridge vents to name a few).
  2. This is not the combustion air needed for your gas furnace and water heaters.

A whole building mechanical ventilation system is a fan designed to bring fresh air into your office or home.  Whole building mechanical ventilation systems are one of the key elements of healthy indoor air, and one of the least expensive components of your HVAC system.

The steps to designing whole building mechanical ventilation system (fresh air system) are as follows:

  1. Determine the required CFMs of fresh air needed in the building based on the size, number of occupants and overall leakiness of the building.  We always refer to ASHRAE standards for determining ventilation needs:
    1. ASHRAE 62.2 for Residential Ventilation
    2. ASHRAE 62.1 for Commercial Ventilation
  2. Determine a strategy for ventilation, what type of system will work best (exhaust only, supply only, or balanced); there are several factors to consider when picking a ventilation system.
    1. How much air does the building leak or will leak after completion/remodel.  If the building is new, you can use energy codes requirements for building tightness, however it's always a good idea to discuss this with a certified RESNET Rater, especially if you've been working with one on past buildings.  If you already live in the house, or are planning a remodel it's always a good idea to have a blower door test performed.  The tightness of a home will help dictate the right ventilation solution for the home.  Super tight homes will work better with balanced systems or supply only with dedicated ventilation fans.  Homes that leak a lot may not need ventilation.
    2. Are there any external factors such as soil gases, damp crawl space/attics, connected garages and/or other bad air sources that we need to be concerned with.  This may rule out an exhaust only system which could potentially put the house under negative pressure and cause the unwanted contaminents to enter the building.
    3. Where is the house located, hot humid climate, cold dry climate, temperate, etc...
    4. How is the building to be heated and cooled?
    5. How will the ventilation system impact the humidity levels in the home?
  3. Once we understand the above factors we can begin to specify a type of ventilation system:
    1. Exhaust only systems, consist of one or more fans connected to an automatic switch to ensure the fan runs enough to meet the prescribed ASHRAE ventilation needs.  This could be as simple as a bathroom fan in a home, or an exhaust port on a commercial rooftop unit.  A major con of this type of system is based on the fact we only know where we are exhausting the air from; we have no idea where the fresh air (or if it's truly fresh air) is being pulled into the house.  This is our least favorite means of ventilation and we believe it should be reserved for local spot ventilation such as bathrooms and kitchens only.

    2. Supply only systems are usually tied into the return plenum (although some systems are independent), and cause a slight positive pressure inside the house (w.r.t. the outside). These include standard fresh air intakes, air cyclers and ventilating dehumidifiers, such as:
      1. Air Cyclers use a damper-controlled inlet to the return of the furnace which will open as necessary to deliver specified amounts of ventilation. (Dampers are capable of closing during extreme weather conditions).  The air cycler relies on the furnace/air handler fan to move air into the home.
      2. Economizers (typically found on commercial rooftop units, with openings on the return side of the unit, to let in fresh air for ventilation and/or economical cooling).  Economizers also typically rely on the main HVAC fan to move air into the building.
      3. Fresh Air Intakes are ducts connecting the return ductwork on an HVAC system to the outside with limited controls.  These also rely on the HVAC fan.
      4. A Dedicated Supply Fan moves air directly into the home, and usually into the return of the furnace.  Examples include simple fans set to move the required amount of air in ventilating dehumidifers which serve to ventilate and to dehumidify homes.
    3. Balanced systems typically (but not always), use either a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV) to exhaust stale air out of the home and bring in outside air at the same rate.
  4. Once the system is decided upon, installation is the final hurdle.  There are many considerations:
    1. Will I have the space for the prescribed ventilation system(s)?
    2. Where will I be pulling air fresh air from, in the case of the supply only and balanced system, the fresh air inlet into the house must be 10' or more from any bad air sources (exhaust flues, dryer vents, exhaust fans, vent stacks), and can I get it off the ground enough to not worry about snow fall blocking the inlet?
    3. How will the system be ducted and how will that impact the flows of the ventilation system?
    4. For any system connected to HVAC ductwork, the normal operating pressure of the HVAC system will impact the ability of the ventilation to operate. Should I test the operating pressure?
    5. All of the items above will impact system performance.
  5. Once the system is installed, it then must be tested and verified to deliver the required ventilation to the building, which requires a certified energy auditor or test & balance firm.

Priority Energy offers expert ventilation design and installation services.  Call us today or fill out the form on this page for additional information - 800.737.2299 

  • Thank you again and you will be the first person I call if I need additional part or service from your company.
  • I just wanted to send this message to all you and say GREAT JOB!  We had a rough inspection today and passed for the Woodward Ave. house. The inspector told us "if every house I inspected looked like this one I would be out a job".

    Anonymous Builder
  • We were so impressed with the amount of information the Priority Energy technicians gave us during our ENERGY AUDIT.  If you are buying a house, I would strongly recommend having them do an energy audit on it, in addition to your usual home inspection.

  • Thanks for a super intelligent and deep seminar expertly handled by a staff which was a pleasure to be around. Lunch was superbly and subtly handled.

    A.S. Architect
  • I wanted to thank you for all of your extra time and energy during our BPI training over the last few weeks. You really helped put things in perspective. You are an awesome crew and your facility is a valuable resource for students and the community

    BPI Student, L.E.
  • There is much less dust in the house and the monthly gas and electric charges have been reduced by 10 to 15%.....I'm sure I will see greater savings over a twelve month period......thanks again.

    Aeroseal Client, R.N.

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