Fliter changes

[Shopco]

Is it possible to quantify the state of my HVAC filter using a manometer?

 

[Lone Star Charles]

A simple answer is "Yes". However, there are a lot of things to take into consideration - type of filter - MERV rating - air flow rate (velocity) - measurement transducer location(s) - how dirty a filter is acceptable to you - etc. Perhaps the easiest way would be to install the manometer, install a brand new filter, turn everything on, and then take a pressure measurement. Over the next day, week, month, or whatever, observe the filter until it is as dirty as you would still be comfortable with. take another pressure measurement. This should give you a reasonable way to determine the state of your HVAC filter in the future.

 

[Sponsor]

 

[Shopco]

I have 4 returns each of which are 20x20x4. I have just ordered MERV 13 filters. How do I connect the manometer? My guess is one line is just open (no tubing) and the other line would go to the plenum where all 4 returns come in. Does that sound right?

 

[Jadnashua]

You want to check the pressure difference between the two sides of the filter...so, one hose would need to go on one side, and the other on the other. I suppose you could leave one side open, and compare the difference when measuring both sides of the filter with the other hose as well.

 

[DonL]

You are better of getting a T-stat that keeps track of run-time. Or just change them when they look dirty.

Even if the filter passes air, It could have mold in it. You should have a Look See.

Some of the expensive T-stats have sensor add on, But I am not sure they are needed, for a home setup.


Have Fun.

 

[Shopco]

I am appreciative of anyone who is willing to respond to me at all; I have learned so much from this forum. However I find I must disagree with DonL. I certainly mean no disrespect, but the methodology he proposes I think only works with big box throw-away filters, because it almost guarantees that the filter will be changed either too soon or too late. One cannot change filters based on time unless one knows the specific conditions under which the filter operates, i.e. is the environment dirty or clean, with high humidity or low, etc. and that situation is stable.

I have just spent $250 on 12 filters (3 changes) and I certainly do not want to change them before it is necessary. To advise a reader (with perhaps fewer critical thinking skills) to just change filters every so often based on some arbitrary time schedule is irresponsible.

 

[DonL]

I was just saying you are better off going by unit run time, then just changing every month or a set amount of time.

Would your Idea work?, of course it will, Is it necessary ?, No.


Have Fun.

 

[NHmaster3015]

You want to be careful with Merv filters especially if you are running A/C The added restriction can often cause the evaporator coil to ice up.

 

[NHmaster3015]

You want to check the pressure difference between the two sides of the filter...so, one hose would need to go on one side, and the other on the other. I suppose you could leave one side open, and compare the difference when measuring both sides of the filter with the other hose as well.

One side of the manometer needs to be open to the atmosphere. If there are multiple check points he either needs multiple manometers or to take readings at each location.

 

[DonL]

One side of the manometer needs to be open to the atmosphere. If there are multiple check points he either needs multiple manometers or to take readings at each location.

I think that was what Jim was saying.

People should look into the price of filters before they buy a unit.

For the price you pay for some of those Filters, the manometer should be built in.


Have Fun, Everyone.

 

[NHmaster3015]

Personally, I think they are a waste of money. There are other and much less restrictive methods for removing particulate and bacteriologic as well as virus bugs, and while the initial cost is more, they will save money in a very short time.

You can make a home made manometer with some clear plastic tubing and a ruler.

 

[Shopco]

“You want to check the pressure difference between the two sides of the filter...so, one hose would need to go on one side, and the other on the other. I suppose you could leave one side open, and compare the difference when measuring both sides of the filter with the other hose as well.”

Since the filters are located in the returns, one side of the filter(s) is just the house, so an open port on the manometer would be reading that. Yes?

“Would your Idea work?, of course it will, Is it necessary ?, No.”

It seems to me that it is necessary if I want to maximize filter life, and @ $80 per change I definitely want to. I do think you could make an argument as to whether $80 worth of filters is necessary. We are trying to reduce dust but I admit there is much I do not know and/or understand about this field.

“You want to be careful with Merv filters especially if you are running A/C The added restriction can often cause the evaporator coil to ice up.”

Point taken but; I have a 1,000sf house with a 3 ton unit and 4, (count them – 4!) 20x20 returns, due to misguided efforts of the first HVAC guy I hired. The second guy thought that since the filters/returns were already there it would not hurt anything to leave them there. Since this gives me over 11sf of 4” filter area my thinking is that I can pretty much ignore restriction concerns. Do you guys agree?

“One side of the manometer needs to be open to the atmosphere. If there are multiple check points he either needs multiple manometers or to take readings at each location.”

My thought was that if I took a reading from the plenum I would get a “collective” restriction reading. If I were to do what is probably the correct way, and measure each filter, I would still be faced with the problem of putting one fresh filter in a system with three partially clogged filters. Air is going to be drawn through the filter(s) with the least amount of restriction. As the filter becomes clogged the air will begin to be drawn more through the next least clogged filter and so on.

Personally, I think they are a waste of money. There are other and much less restrictive methods for removing particulate and bacteriologic as well as virus bugs, and while the initial cost is more, they will save money in a very short time.

I am very interested in these methods. Would you elaborate?

A Note: I hope I am not coming off as argumentative or picky. My only objective is one of understanding and I thank you all for your patience, not to mention your expertise.

 

[DonL]

All you need to do is put a Plastic BB in a straw and Poke it threw your filter. You get the idea...

Mark where the ball is with a clean filter, and it will tell you when the filter has restricted flow.


Simple science experiment.

 

[JerryR]

Boy, you've got a heck of a lot of filter area for a 3 ton unit.

I've got 2 homes with a 4 ton unit and a single 24x24x1" filter.

I've got another 3000 sq ft under air home with a 4 ton AC with variable speed air handler and 2 zones. In that house I have 3 returns, all with 1" filters. 2ea 20x20x1" filters and 1ea 12x12x1" filter

I let my thermostats tell me when to replace filters based on run times. I still inspect filters every 30 days just to be sure.

After a recent tile renovation I was changing filters weekly.

I use merv 8 routinely. I was warned not to use height Merv filters with newer air handlers. Newer variable speed AC air handlers throttle speed to maintain constant CFM. Restrictions cause expensive motor burn outs.

 

[DonL]

I was warned not to use height Merv filters with newer air handlers. Newer variable speed AC air handlers throttle speed to maintain constant CFM. Restrictions cause expensive motor burn outs.

A variable speed blower may make a manometer indicator useless, Never really put that into the equation. Good Point.


After reading this again;

"Is it possible to quantify the state of my HVAC filter using a manometer?"

You do not need a manometer, Just counting the number of filters you have, That will tell you the quantity you have.


Have Fun.

 

[Reach4]

A variable speed [constant CFM] blower may make a manometer indicator useless, Never really put that into the equation.

With such a blower, a manometer across a filter would be even more effective at identifying filter clogging.

 

[DonL]

With such a blower, a manometer across a filter would be even more effective at identifying filter clogging.

Ok.

That is cool. I guess we went to different schools.

It is great to have you on the forum when I have my head up my ass.



It is very dark in here, Please Help.

Seems like monitoring fan speed would be a better option.

 

[Lone Star Charles]

Just Googled "Inclined Manometer Air Filter Gage" and saw this - http://www.****.com/itm/INCLINED-MANOMETER-450-AF-AIR-FILTER-GAUGES-DWYER-/221207084341 - I used Dwyer gauges during my career and found them to be very good. As you suggested, you could leave the high pressure side of the gauge open and put the low pressure side in the plenum and then just observe the increase in pressure drop over a period of time. When the filters get as dirty as you want to tolerate, just move the gauge marker to that level and change the filters. The next time the pressure drop gets to that level, you can change again.

You will notice that there are two static pressure pickups included in the kit. These are designed to be installed so that the pickup tubes are parallel to the airflow. In your case, I think that I would just leave the high side open and put an open tube inside the plenum - It's just that you don't want any pitot pressure to influence the readings.

 

[Shopco]

Thanks LSC. You got me thinking about tube orientation within the plenum. On an airplane you had the dynamic port (pitot tube) and the static port, with the static port perpendicular to the airflow. That is what I would assume the orientation should be. Yes?

 

[DonL]

You may be able to find some T38 pitot tubes from Gov surplus.

They have the Temperature sensor also.


Have Fun.