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Air is not toothpaste

I"d like to correct an assumption several homeowners have.  Air is not like toothpaste!

That is to say that you cannot close off vents in the basement and expect the air to come out upstairs.  A residential furnace or heat pump does not have the power to do that. I have seen on numerous occasions, a blower from an air handler or furnace with the fin’s completely wiped off the wheel.  It can also cause premature failure of the blower motor. If the furnace or air handler is old and has a PCS (permanent split capacitance) motor, and it keeps failing ask your technician about static pressure.  The situation may make sense to replace the furnace or air handler. This would alleviate the static pressure issue and potentially save you money on utility costs.

It's all about static pressure.  That is to say the pressure in a container that pushes out against all surfaces.  Your duct work is the container. Most homes are engineered to not exceed a maximum static pressure.

Static pressure is one of the most important factors in HVAC design. Simply put, static pressure refers to the resistance to airflow in a heating and cooling system's components and duct work. The push of the air must be greater than the resistance to the flow or no air will circulate through the ducts.Dec 4, 2014

Static pressure – what is it and why is it important? Dominion Service ...

So when enough registers are closed the static pressure goes up, that causes back pressure on the blower wheel fins which causes them to fail.

If there is truly an imbalance on where the air is and where it is needed.  There are significant changes that have to be implemented.

The thing that a technician should check is static pressure.  He has the knowledge and expertise to perform this test. Once the accurate static pressure is known the technician can advise on how and where to make modifications to balance the system.

Some modifications are as simple as throttling down some registers.  Ensuring the static pressure is not increased. More in depth a technician may have to add dampers in the duct near the source of air.  There may also be a need for a bypass damper. This is automatic and allows back pressure to go from high to low thus lower overall back pressure.

The good news is that there are now smart furnaces that monitor back pressure on their own.  They can modulate the pressure to ensure the exact right amount of air is provided. They do this in most cases by the way of a variable speed blower.  The controller that adjusts the blower can makes changes every second. This enables the blower to be very efficient.

When someone tells me there furnace or air handler is old my standard reply is “So am I and I still work !!”.  However with advent of new more efficient motors I have to rethink using that statement.. Most manufacturers claim that a new more efficient HVAC system can save as much as 30% on overall utility costs.  When your looking at higher and higher utility bills 30% is a lot.

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