I am trying to quanitfy the energy savings that is generated by having clean furnace filters installed. the furnace filter manufacturers have good data regarding air quality but what does a dirty filter do to the performance of the furnace? 

Views: 405

Reply to This

Replies to This Discussion

To get the conversation going...

Let me start by saying I don't have a complete answer to your question but thought I would throw this out for discussion.

I welcome comments.


You can measure the performance difference of the blower between a system with a clean filter and a system with a dirty filter.The measurement will be precise for that one system given those specific filters at that point in time. But it would be hard to apply that to other systems. I don't know if that is of use to you. Also, that is only the blower. I have some thoughts on measuring the rest of the system but they are weak. See below.


In order to measure the blower performance you need some way of measuring the energy use of the system.

You could use an Amp meter (Fluke makes a good one) or an energy mgmt device like (e.g. TED  http://www.theenergydetective.com/).

Once you have the energy mgmt device in place, run the system* with the old filter and note the energy use.

Replace the filter and take a new measurement.

Subtracting those two measurements will give you the energy wasted due to the blower.

That should be pretty accurate.

I ran a similar test trying to determine the performance difference with a barometric bypass open vs closed. I ran this test because I suspected the bypass was setup incorrectly and eating to much energy. My test proved my theory with real data.


However, you still need to account for the energy wasted from the heating system.

I have no great ideas here but will suggest the following two ideas as a better than nothing solution. I have little confidence of the accuracy of either of these but it might be better than nothing for a ballpark number and it opens up the discussion.


1. Use a ratio of the good filter to bad filter energy use and the system rated efficiency to the "bad filter" efficiency.

ex. Blower used 1000 watts with good filter and 1200 watts with bad filter. Furnace is 95% efficient (per mfg).

good filter energy / Bad filter efficiency = good system efficiency /bad system efficiency (BSE)

1000w x 1200 w  = 95% x BSE   or BSE = 88%


2. Calculate the additional time that the system has to run due to the inefficiency. Then calculate the fuel cost of that additional time (based on mfg data).

If the system is moving 800 cfm with a clean filter and we calculate the blower is only about 83% efficient  (1000w/1200w), with a dirty filter then the system is pumping 664 cfm. To get the same total volume of air, the system with the dirty filter would need to run 20% more (664cfm x 120% = 800 cfm).

For calculation purposes, let's assume the cost to run the system is $1 per hr per mfg specs, and the system is running 10 hrs per day. It would thus cost an additional 2 hrs and thus $2 per day with the dirty filter.


Bonus option: Use both of the above methods and average them out.




Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Profile IconShandi Whited, Noah Sanders, Edward G Fahrenkrug Jr and 2 more joined Home Energy Pros
1 hour ago
Alan Gindt replied to Alan Gindt's discussion Minneapolis Blower Door System for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Bob, sorry but it has been sold"
1 hour ago
Bob Mariani replied to Alan Gindt's discussion Minneapolis Blower Door System for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Is this still available?"
4 hours ago
Eric Kjelshus replied to John Gillis's discussion Energy Savings of Whole House Fans vs. Air Conditioners in SoCal Featured on New 'Ask This Old House' Season in the group News & Announcements
"2000 SF house in Kansas City needs a 36" whole house fan or about 8,000 CFM takes a 1/4 HP fan…"
13 hours ago
Eric Kjelshus joined Diane Chojnowski's group

News & Announcements

Share your news and announcements with the community in this group.See More
13 hours ago
Eric Kjelshus replied to David Byrnes's discussion Insulation machine preferences
"If you find over heating look at voltage/amp draw very hard.    I find if you have…"
13 hours ago
Colin Genge posted events
15 hours ago
Adrienne DeAngelo posted an event

GreenPoint Rated CORE Training at Best Western Plus Marina Shores Hotel

October 15, 2015 to October 17, 2015
Increase your certifications or get to know the GreenPoint Rated system so that you can work more…See More
16 hours ago

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service