Author Topic: Static Pressure Issues  (Read 269 times)

Offline Viperi

  • 313D Supporter
  • ****
  • Posts: 46
Static Pressure Issues
« on: April 07, 2017, 07:55:44 PM »
Hey guys im new to this field and i recently got a manometer and tested my own furnace. My furnace spces for .5 wc

Between the furnace and filter + between furnace and coil i get 0.7wc

Across the filter is .3

across the coil is .2

between furnace and filter .4

between coil and furnace .3


what can i do to bring the static down?

what are normal readings at certain test areas?

Offline Admin

  • Administrator
  • *****
  • Posts: 1778
    • HVAC TECH GROUP
Re: Static Pressure Issues
« Reply #1 on: April 07, 2017, 09:18:06 PM »
I attached a diagram with some common readings.  You seem to have a return air restriction.  Trying adding a return air and see if the static pressure decreases.  What kind of filter are you using?

Offline tenletters

  • 313D Supporter
  • ****
  • Posts: 30
Re: Static Pressure Issues
« Reply #2 on: April 08, 2017, 08:09:38 PM »
Hey guys im new to this field and i recently got a manometer and tested my own furnace. My furnace spces for .5 wc

Between the furnace and filter + between furnace and coil i get 0.7wc

Across the filter is .3

across the coil is .2

between furnace and filter .4

between coil and furnace .3


what can i do to bring the static down?

what are normal readings at certain test areas?

Inserting your manometer (on a system with a external static pressure of 0.50'' wc):

1. before the filter you should not get higher than -0.15'' wc. Higher suggests that you have an undersized return or a restriction in the return creating more of a negative reading.

2. in your supply duct you should be no more than .35'' wc. Higher than this suggests undersized supply duct or restriction

-0.15'' + 0.35'' = 0.50'' wc external static pressure

Now what I hear from people is that it doesn't matter if you get a .45 reading for example on the supply as you'll just increase the airflow. You're not and you're also going to hear that airflow through the house. A blower is designed to deliver a certain CFM against a certain external static pressure reading (on the furnace rating plate). If the blower is designed to deliver 1200 CFM against a static pressure of .50" wc, then if the static pressure is more than .50" wc the blower is going to deliver less CFM than 1200.

Normal pressure drop across a filter should be no more than 20% of the static pressure rating, so about -0.1'' wc with your return air size being 2 sq in for every 1,000 btu of the furnace output.... will you ever see that? no probably not too often.

Pressure drop across your coil should be about 0.20'' wc - 0.25'' wc.

You probably have a filter issue. A 1'' merv 11 filter is not the same as a merv 11 5'' filter. The 5'' filter is going to allow for better airflow as there's more space to move.

Offline Viperi

  • 313D Supporter
  • ****
  • Posts: 46
Re: Static Pressure Issues
« Reply #3 on: April 14, 2017, 08:15:03 PM »
thanks for the reply. im still very confused as both your examples are opposite regarding the supply and return "normal" readings

Offline Admin

  • Administrator
  • *****
  • Posts: 1778
    • HVAC TECH GROUP
Re: Static Pressure Issues
« Reply #4 on: April 15, 2017, 05:24:25 PM »
You can download another static pressure guide - Here

Offline tenletters

  • 313D Supporter
  • ****
  • Posts: 30
Re: Static Pressure Issues
« Reply #5 on: April 15, 2017, 09:57:23 PM »
Quote
thanks for the reply. im still very confused as both your examples are opposite regarding the supply and return "normal" readings

Whatcha confused on exactly so we can explain the theory of?

Offline Viperi

  • 313D Supporter
  • ****
  • Posts: 46
Re: Static Pressure Issues
« Reply #6 on: April 20, 2017, 05:16:53 PM »
Quote
thanks for the reply. im still very confused as both your examples are opposite regarding the supply and return "normal" readings

Whatcha confused on exactly so we can explain the theory of?

thanks for your explanation. i understand it alot more now thanks!

Offline tenletters

  • 313D Supporter
  • ****
  • Posts: 30
Re: Static Pressure Issues
« Reply #7 on: April 20, 2017, 08:04:38 PM »
Quote
thanks for the reply. im still very confused as both your examples are opposite regarding the supply and return "normal" readings

Whatcha confused on exactly so we can explain the theory of?

thanks for your explanation. i understand it alot more now thanks!

Awesome. Knowing these will help as a tech

Offline mustang8

  • ***
  • Posts: 2
Re: Static Pressure Issues
« Reply #8 on: May 10, 2017, 09:36:38 AM »
Thax man ..
its a great piece of information clearing all doubts of static pressure and CFM.
but when u need to check static pressure.. ???