i have a gas fired 2 stage 80% daikin furnace. that a local HVAC company installed in march of 2018. last winter they recommended moving from a merv 8 - 1" to a 13 - 2" which i did. tech came out last week for annual tune up and tested the air pressures in ways that he, or any one else from the company, had not done before and is telling me the 13 is too much. the furnace has an ecm motor - but even so the tech said the pressures are too high from the filter.
previously they had tested only from point (1) before the filter to after the blower at point (3) - which i understand is not a good measure? I am curious about this...does this measurement provide any helpful information? if not, is this an old HVAC myth that has been proven not to work? If so when did the change in thinking about this come about? Just trying to understand all of this.
photo shows 3 openings for testing. here are the tech's results:
1: -0.18 (before filter)
2: -0.81 (after filter - but before blower) - result 0.63 "pressure drop" per tech
and
2: -0.86 (before blower)
3: 0.07 (after blower) - "static pressure of 93"
Tech said static pressure is too high, should be 50-75 and to use a lower merv filter. I was able to duplicate their readings + or - a point or two with my manometer. I did so several different ways, with a single short hose, with & without a probe as well as two hoses w/ probs. All very close to each other.
The info I've seen on line focuses on the measurement between 2 & 3 as static pressure. What, if anything, does the first measurement between 1 & 2 tell me? What does the measurement between 2 & 3 tell me? Is their conclusion correct regarding the static pressure and need to reduce the Merv?
I would like to have as high a merv filter as possible without stressing the motor (ECM) and also be able to use future pressure testing to tell me when I should put in a new filter but am unsure how to do so.
Thanks in advance,
Jim
ps
this is the same company that said you save fuel by keeping your house at the same temp day & night as opposed to setting it back at night. tried to explain to them they were wrong but didn't get very far.
when i talked to the manager who had told me to use the 13 and the tech's new information and as to where the new testing hole # 2 was added and used he said he hadn't heard of that before....perhaps new training?
previously they had tested only from point (1) before the filter to after the blower at point (3) - which i understand is not a good measure? I am curious about this...does this measurement provide any helpful information? if not, is this an old HVAC myth that has been proven not to work? If so when did the change in thinking about this come about? Just trying to understand all of this.
photo shows 3 openings for testing. here are the tech's results:
1: -0.18 (before filter)
2: -0.81 (after filter - but before blower) - result 0.63 "pressure drop" per tech
and
2: -0.86 (before blower)
3: 0.07 (after blower) - "static pressure of 93"
Tech said static pressure is too high, should be 50-75 and to use a lower merv filter. I was able to duplicate their readings + or - a point or two with my manometer. I did so several different ways, with a single short hose, with & without a probe as well as two hoses w/ probs. All very close to each other.
The info I've seen on line focuses on the measurement between 2 & 3 as static pressure. What, if anything, does the first measurement between 1 & 2 tell me? What does the measurement between 2 & 3 tell me? Is their conclusion correct regarding the static pressure and need to reduce the Merv?
I would like to have as high a merv filter as possible without stressing the motor (ECM) and also be able to use future pressure testing to tell me when I should put in a new filter but am unsure how to do so.
Thanks in advance,
Jim
ps
this is the same company that said you save fuel by keeping your house at the same temp day & night as opposed to setting it back at night. tried to explain to them they were wrong but didn't get very far.
when i talked to the manager who had told me to use the 13 and the tech's new information and as to where the new testing hole # 2 was added and used he said he hadn't heard of that before....perhaps new training?
source https://hvac-talk.com/vbb/showthread.php?2223403-trying-to-understand-manometer-data&goto=newpost
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