Static Pressure: What is it and Why is it Important?

Tech Tips

Aug 28, 2024

Just as high blood pressure can indicate a problem with your health, high static pressure indicates a problem with your HVAC system and ductwork. In a technical sense, static pressure refers to the amount of pressure measured in inches of water column when air moves through an object, such as the ductwork in your house.

Two things that contribute to static pressure are either insufficient ductwork on the supply side, or inadequate return coming to the furnace or air handler.

Take a straw, poke three holes in it with a pin, and blow on the end of the straw - air will take the path of least resistance and come out the end. Now in the same example, put your finger over the end and blow - air now is directed through the small holes that you poked into the straw; this demonstrates static pressure in action.

If you shrink the size of the holes in your ducts, it increases the velocity of the air coming out. If your static is low, you would taper or decrease your trunk, or take off diameter to increase the velocity of the air moving through it - thus increasing the static.

With an improperly sized air distribution system, you can expect noisy system operation because your fan motor must work much harder to overcome the high static back pressure. You are trying to move a higher volume of air than your ducts can handle, which increases the air pressure, and therefore, the noise.

In addition, you risk burning out your circulating fan motor, longer system run times, premature failure of the heat exchanger, or evaporator freezing problems.

For starters, invest in a dual port manometer. Educate the end user on the importance of static and the role it plays in the HVAC system and overall comfort in the conditioned space. Understand the maximum or total static pressure the equipment can handle.

IMPORTANT INFORMATION: Did you know? Daikin equipment can only handle a total e.s.p. of 0.5” of static, and Airease/Ducane can handle 0.8” of total e.s.p.

RSL’s technical support team recommends that every HVAC estimator should carry a dual port electronic manometer, just like the Fieldpiece SDMN5K1 and the ASP2 static pressure probes. If they took a static pressure reading during the estimate process, they could potentially identify problematic systems ahead of time, before installing the new equipment.

Filters also contribute to the system total static pressure and play an integral role. If we look at the pressure drop across the popular 3M brand of Filtrete air filters (that many homeowners buy from box stores such as Home Depot or Canadian Tire), we can see that these filters have a huge pressure drop, and that shows when the filter is clean.

When filters build up with pet hair, dirt and dust, the pressure drop increases up to 1.0” e.s.p., thus increasing the total static throughout the system.

For any further enquiries into static pressure, you can contact your local branch to ask any questions you may have. Alternatively, you can email the RSL Online Sales team, and your query will be passed on to the relevant department.