With the change to newer, smarter motors, comes with a new problem that was not as big of a problem back in the day, static pressure. You’ve seen how big your duct work is in the basement, right? And you may notice at key points the duct work can even start to shrink. This is all to balance out your duct work to keep your home as evenly heated and cooled as possible.
Static Pressure is the term we way we can measure just how much restriction your blower motor has to fight to push and pull air around your home.
It’s just like blood pressure.
What sounds like a silly analogy is really more related than you think. Just equate Duct Work to bloodstream, and Blower Motor to your heart…
- Most homes have duct work that cause higher than the “perfect” range they recommend.
- Having higher numbers doesn’t necessarily mean problems today, but it could in the future.
- We can address the problems with some simple fixes that do not break the bank.
- For more severe numbers we may have to look at rebuilding part of the duct work.
- Severe numbers can cause blower motors to fail much faster than their normal expected life.
Air flow is lazy and it will always find the easiest way out of the system. There is also only so much air flow that can reasonably flow through duct work based on the size of the trunk line or the register. Can you push more than stated? Yes. Does it take incredible amount of energy to do this? Yes. Do these new high efficiency blower motors like to do this? No.
So new motors have this problems? Old ones didn’t?
Modern motors are trying to save you money, and they do. When you compare blower motor power draw between the old and new, you see around ~20-25% savings when it is at full speed. If you leave your system in circulate when there isn’t a call for heating or cooling (aka “Fan On” switch on the thermostat), it will do this ~70-75% less power, because it can really step down into a slower speed (if it’s a full ECM motor). Part of this is done by running smarter.
A full ECM motor (aka Variable Speed motor) will sense the restriction based on resistance as the blower shaft rotates and will try to counteract this by speeding up to ensure the furnace or air conditioner is moving the right amount of air. It is working to protect your equipment. If your heat exchanger is not getting enough air flow, the heat exchanger is going to keep heating up and trip a safety control and it can shorten the life of your heat exchanger / furnace.
Both units deal with static pressure. The old motor just keeps doing what it’s doing, where the new motor is trying to protect your equipment, and it will do everything to keep the set air flow speed, and if that means overworking itself, it will.
So what are acceptable ranges?
This is a great question. Manufacturers will tell you 0.50 WC or less is where you want to be. We can tell you with great confidence that this is a fools errand for most homes, and with the filtration systems and older home design, you are not going to be getting this, and THAT IS OKAY.
We check the static pressure on all of our installations to ensure you are going to have a long lasting healthy furnaces. The ranges that we consider acceptable vary based on the equipment, the house structure, and more…
| Acceptable Range | We will leave the system as is, and no further modifications are needed. While it may not be perfect, it is plenty acceptable. |
| On-The-Job Fix | We notice it is high but not extreme numbers. We are going to add in 1-2 registers on your furnace strategically to get numbers back in line. |
| Revisit | If your numbers are considering extreme, we will communicate it to your estimator and they will work out a plan to tweak things. Our goal is to do things as sensible as possible, to save you money! |
Don’t get bullied about Static Pressure.
Yes, static pressure does make a difference LONG TERM with your system, and it’s good to get it into a reasonable range. From our research and experience we believe manufacturers set such low numbers on their static to protect them from fault. They know most homes will not remotely hit those ranges, and they publish these as a scape-goat.
We are in so many homes throughout the year, and it’s incredibly rare that we ever have to spend thousands reinventing duct work for a customer. Most of the time strategic adjustments, and additional registers will help solve this issue.
In only extreme cases may we request a customer to sign something saying we explained the high static pressure and it cause premature failure, and that they did not wish to make changes at this time. Other companies use this more as a sales tool, we just save it for the most extreme of cases to protect our keister.