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?
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?
Quote from: Viperi 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?
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.
thanks for the reply. im still very confused as both your examples are opposite regarding the supply and return "normal" readings
You can download another static pressure guide - Here (http://www.hvactechgroup.com/files/Static%20Pressure.pdf)
Quotethanks 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?
Quote from: tenletters on April 15, 2017, 09:57:23 PM
Quotethanks 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!
Quote from: Viperi on April 20, 2017, 05:16:53 PM
Quote from: tenletters on April 15, 2017, 09:57:23 PM
Quotethanks 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
Thax man ..
its a great piece of information clearing all doubts of static pressure and CFM.
but when u need to check static pressure.. ???
Quote from: tenletters on April 08, 2017, 08:09:38 PM
Quote from: Viperi 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?
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.
Great info in this post but. U say
-0.15'' + 0.35'' = 0.50'' wc external static pressure
Wouldnt that be .2"
Quote
Great info in this post but. U say
-0.15'' + 0.35'' = 0.50'' wc external static pressure
Wouldnt that be .2"
Nope. I once questioned that too as it seems confusing when you think back to some basic math rules. But the reason you still add both the negative and positive readings together is because each one is a type of resistance and we want the grand total. So the negative (or return side) is still part of the overall static pressure.