Ask Dirk: What does the V stand for in HVAC?

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We talk about your HVAC system all the time, and it’s easy for us to speak in jargon like saying HVAC instead of heating, ventilation and air conditioning. And while the V-for-ventilation is very important to us when we are checking your system, you may not know what it means, or why you should pay attention to it, especially during our recent unprecedented air quality events.
Here’s why ventilation is so important.
Simply put, ventilation is the exchange or replacement of air in your space. It is responsible for providing better air quality by diluting pollutants that already exist indoors like volatile organic compounds (VOCs) which are found in a number of household items including paint, cleaning supplies, building materials and furnishings; bacteria; viruses and carbon dioxide. The air that is exhausted will carry some of that unpleasantness out as well.
Ventilation also replaces the stale air in your space with fresh air. Fresh air from outside is brought inside and stale air from inside is sent outside. Ventilation strategies allow you to control the origin of the air that enters your home.
Without the proper strategy, much of the air entering your home likely comes from places where the “new” air is not very fresh, like the crawlspace and the attic.
Most homes, especially older homes, have nothing in the HVAC system that provides any “V.” Instead, they are “ventilated” by infiltration. Air leaks into and out of the home through doors and windows that are leaky, and from the crawlspace and attic because there are leaks around heating and cooling duct openings, access panels, light fixtures, electrical and plumbing paths, and so on.
This is not ideal because the new air may not be very fresh, especially that from the crawlspace and attic The quality of indoor air can be significantly improved by sealing against infiltration and providing a controlled, conditioned source of fresh air, distributed by your forced-air HVAC system.
Newer homes and homes that have been weatherized have less natural infiltration of outdoor air and need ventilation even more than older homes.
So, how does ventilation work?
Your mechanical system is truly a wonder. Properly done ventilation filters the outdoor air as it is brought into your home, ensuring that it does not increase the levels of pollen, dust, and other outdoor pollutants in your home.
The simplest first step for the forced-air systems that are typical in homes is to add a small duct that connects to your return air duct and runs to an outside location where clean air can be accessed. Fresh air is mixed with the air in the return duct and is distributed through the supply ducts to every room that has a heating and cooling register.
This will typically create a small, undetectable positive pressure in your home and will cause indoor air to be exhausted through the imperfections in you home that are usually infiltration pathways, turning them into exfiltration pathways.
Appropriate filters need to be a part of this fresh air supply to prevent introducing more pollen, dust, or smoke into your home. There may even be a damper mechanism that will allow you to block outside air if it’s too bad.
Temperature-controlled ventilation
It should be noted that outside air that is not filtered and conditioned may bring allergens, smoke, and dust inside and may be much hotter or colder than the desired indoor temperature, negatively affecting indoor temperature.
Extreme cold and extreme heat conditions enforce a higher energy penalty on fresh air. Too much fresh air can hurt energy efficiency when the outside air is not at the temperature that you want indoors.
Disabling ventilation can be done manually or can be automated with a temperature control connected to your ventilation of choice. However, while disabling ventilation during temperature extremes can save on energy costs, it does so by lowering the quality of your indoor air.
More sophisticated ventilation solutions
More sophisticated solutions include heat-recovery ventilators and energy-recovery ventilators that condition incoming air using the air that is being exhausted, making the temperature of the incoming air closer to the indoor temperature.
Some systems include controls that only operate the ventilation system when CO2 levels reach a certain point (CO2 is a good proxy or indicator of the level of indoor pollutants) and that prevent operation when outdoor temperatures are very cold or very hot.
If your heating and cooling are provided by means other than a central forced-air system it will probably be necessary to provide ducts or another means of bringing fresh air into your home and exhausting air to the outside.
As with any indoor air quality situation, we recommend speaking with your trusted HVAC contractor to understand your options and give you the information you need for your system.
Roper’s Heating and Air Conditioning is located at 2062 S. Edmonds Drive in Carson City. For information, visit


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