Seattle Home Inspector's Blog

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Sometimes things just go round and round and round.

It is common knowledge that when your furnace filters get plugged it makes the blower work harder---thus consuming more energy and shortening the life of the blower.

But!

But, just like “common sense,” “common knowledge” is also not as common as one might think.  In actuality, the opposite is true.  The more restricted the ductwork---the dirtier the filters---the less energy is consumed and the easier the blower will run.  (Obviously, in the long run more energy will be consumed because of the added time it will take to heat your house.)

The fact that this is true, seems almost counter intuitive; and hence the ease with which the myth became established.  I have even heard HVAC technicians spew this wisdom and it is very common to hear home inspectors state it as if it were obvious.

In this first picture you can see the amount of amperage been drawn during normal operation of my fully operational furnace with just cleaned filters---6.8amps.

Blower amerage functioning properly

So now let’s restrict the air flow by installing a piece of plywood in the extra slots of the air cleaner.  This will completely cover the air return to the furnace---making the duct more restricted than most dirty filters would ever make it. 

If I am wrong the motor is going to work very hard, the amount of amperage drawn will be significantly higher and I will have a lot of egg on my face.  But then,in all likelihood, this post would not be here.

Air cleaner Plywood duct block Blocking the duct

As you can see by the second reading on the amp probe the amount of amperage is significantly less---3.7amps---meaning the blower is working much less hard. It is consuming approximately 50% less energy.

Amperage with the duct closed off

Essentially the blower is just going around and around and around.  Because the blower isn’t doing any “work”----pulling air----it just sits there and spins. 

So what is the real issue with dirty filters?

If they become too clogged there will not be enough air moving through the heat exchanger and it can overheat.  This can shorten the life of the heat exchanger/furnace. 

In some respects I wish the myth was true because a ruined blower motor is cheaper to fix than a ruined heat exchanger.

 

Charles Buell, Real Estate Inspections in Seattle

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Seattle Home Inspector

 

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Comment balloon 46 commentsCharles Buell • December 13 2012 06:33AM

Comments

Another great post by Charles!  I  continue to learn from your posts and have another thing to look for!

Posted by Kristin Johnston - REALTOR®, Giving Back With Each Home Sold! (RE/MAX Realty Center ) almost 6 years ago

That's why it's important to have a good and credible home inspector.  Good post!

Posted by Larry Bettag, Vice-President of National Production (Cherry Creek Mortgage Illinois Residential Mortgage License LMB #0005759 Cherry Creek Mortgage NMLS #: 3001) almost 6 years ago

I just changed out my furnance filters yesterday.  Yea me.  Great timing on reading this post!

Posted by Cindy Edwards, CRS, GRI, PMN - Northeast Tennessee - 423-677-6677 (RE/MAX Checkmate) almost 6 years ago

What a great explanation Charles. .now I get it!

I learned something new today. .thank you

 

Posted by Fernando Herboso - Broker for Maxus Realty Group, 301-246-0001 Serving Maryland, DC and Northern VA (Maxus Realty Group - Broker 301-246-0001) almost 6 years ago

Charles, 

Absolutely brilliant and simple in explanation for everyone to understand.  Keeping a clean filter is key!   

All the best, Michelle

Posted by Michelle Francis, Realtor, Buckhead Atlanta Homes for Sale & Lease (Tim Francis Realty LLC) almost 6 years ago

Kristin, I always love seeing your smiling face---and so often the first to comment on my post! :)  I have glad you find my posts useful---thanks.

Larry, thanks

Cindy, you would be surprised at how many homeowners don't even know they have one :)

Fernando, I think this will be a surprise to many folks.  Heck, it would have surprised me a few years ago :)

Michelle, yes---keep them clean---it will save your furnace and your energy bill in the long run

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Great

Posted by Roger Pearson Crye, Leike Florence AL (Crye-Leike Florence Branch) almost 6 years ago

Yes to this post and thank you because it is hard to remain ignorant after reading this....good job Charles

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) almost 6 years ago

Charles, in this case low amperage does not equate to higher efficiency. Great point!

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA almost 6 years ago

picky, picky, picky  ;-)

Posted by Alan May, Helping you find your way home. (Coldwell Banker Residential) almost 6 years ago

Charles -- your pictures make your point very vividly, so any who read your post are not soon going to forget its message.

Posted by Steven Cook (No Longer Processing Mortgages.) almost 6 years ago

 Charles - So now I'll have another good argument for not changing my filters. ("Honey, just look at the money we're saving")

Thanks for the enlightening post!

Posted by John Mulkey, Housing Guru (TheHousingGuru.com) almost 6 years ago

Roger, thanks

Richie, even with the facts some will go test their own furnace :)

Michael, exactly---time always must be taken into account

Alan, yup :)

Steven, I think it is pretty convincing :)

John, yes---until the bill for the new furnace comes :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

You have an interesting way of getting to your point... It's distressing that myths are perpetuated by so-called professionals. 

Posted by Olga Simoncelli, CONSULTANT, Real Estate Services & Risk Management (Veritas Prime, LLC dba Veritas Prime Real Estate) almost 6 years ago

Olga, true, and the devil is in the details.  As long as the filters are being changed for "some" reason everything may be good to go.  I think where this is useful is due of the much greater expense of replacing the heat exchanger as well as the dangers of combustion byproducts possibly finding their way into the home if the heat exchanger fails.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

And what a great reminder for me -- THANKS!  Better check my furnace filter and probably just replace it!!

Posted by Carla Muss-Jacobs, RETIRED (RETIRED / State License is Inactive) almost 6 years ago

You must have the tool for every application that the house may have.  How big is your work bag?

Posted by Paul S. Henderson, REALTOR®,CRS,, Tacoma Washington Agent/Broker & Market Authority! (RE/MAX Northwest.) almost 6 years ago

Carla, gotta keep the air moving

Paul, are you trying to goad me into post that picture of me wearing nothing but my tool belt again? :)  Pretty much everything I need fits in the tool belt I wear---a few things I might have to run back to the car for---like combustible gas detector.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Dang, You just got to love an experiment. Well done Mr Buell. I assumed the myth also now I have to recant my thinking, ouch.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) almost 6 years ago

Hey Don, this would make a good "truth or dare" question, don't you think?

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

It's well known(?) clogged filters will damage an A/C coil by freezing it. It sure seems logical it would also be true of heat exchanges. It also makes complete sense now that I see the amperage that a fan pulling no air would work less than one sucking on it. Oh by the way air conditioners are something we use here in CT :)

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 6 years ago

Jim, yes---I should have included that as well---shows how much I see them :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Did you do a test with only a couple of holes drilled in the luan?  That might mimic a lower quantity of air caused by a clogging or clogged filter.

That fact that with NO air drawn is most interesting.  See what happens when less and less air is drawn as the filter clogs.  Start with a couple of holes, and add a few with each subsequent test.  I'd love to see what happens!

Super blog as always.  Seeing it late I cannot suggest it!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 6 years ago

Jay, as you pull out the plywood the amperage goes up

 

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

I love this post. Things do just go round and round. But you are right, you have to know about commons sense and common knowledge. You do so many good posts and I learn so much from you.

Posted by Ginger Harper, Your Southport~Oak Island Agent~Brunswick County! (Coldwell Banker Sea Coast Advantage) almost 6 years ago

I can see how this would be the case. You save electricity but the heat is wasted and not delivered to where it needs to go so I guess the electric savings wouldn't be any good.

Posted by Rob Ernst, Reno, NV-775-410-4286 Inspector & Energy Auditor (Certified Structure Inspector) almost 6 years ago

Ginger, thanks---glad to have you hanging out at my blog :)

Rob, nope---it is not going to help a bit

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Great post Charlie,

You are Seattle's answer to the TV Show "Myth Busters". Imagine what you could do with their budget!

Thanks for a very visual and easy to follow explanation.

 

Posted by Kim Mulligan, Selling Homes for the 21st Century (Homesmart TRG) almost 6 years ago

That's very interesting and the facts are indisputable.  I love a good reality check.

Posted by Rafi Footerman, Home Inspector, Mold Inspector, Radon and More! (Mid Jersey Inspections) almost 6 years ago

Hi Kim, so nice to see you---Mythbusters is sort of my "dream job" :)

Rafi, we all need them now and then.  I have a picture in my head of every home inspector that reads this, running down to their basement and verifying this :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Charles:  Glad to hear you're a MythBusters fan.  I'm still going to just clean my filters on time, regular basis.

Posted by Lyn Sims, Schaumburg IL Real Estate (RE/MAX Suburban) almost 6 years ago

Good information... I always seem to learn something everyday from things that others post here. Congrats on being featured! ;)

Posted by David Evans, HUD NLB Cumming GA (RE/MAX TOWN AND COUNTRY) almost 6 years ago

Good information! Although we don't use our furnace much (we have a wood stove) my husband is fanatic about changing the filter regularly.

Posted by Marte Cliff, Your real estate writer (Marte Cliff Copywriting) almost 6 years ago

Good Morning,

Contact Charles Buell for all your Seattle home inspection needs. Keep up the good work. Have a nice weekend.

Posted by Will Nesbitt, Nesbitt Realty is a family-run brokerage. (Nesbitt Realty at Condo Alexandria) almost 6 years ago

Lyn, Mythbusters are just too much fun.  One of my favorites is when the bust the myth about the "bull in a china closet."

David, thanks---glad you enjoy the posts

Marte, it is certainly a good idea to keep them clean

Will, thanks

 

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Great post ..

 

 

 

 

 

 

Posted by George P. Cruz Sr., PSL FL CDPE, TRC, CIPS (DR Horton) almost 6 years ago

My man you are the MythBuster. Good job.

Posted by Dana Basiliere, Making deals "Happen" (Rossi & Riina Real Estate) almost 6 years ago

George, thanks

Dana, in my own small way perhaps :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Charles, thanks for educating us on the issue of restricted air flow.  This is a good post to share with all homeowners.

Posted by Sharon Parisi, Dallas Homes (United Real Estate Dallas ) almost 6 years ago

Sharon, thanks---just going round and round isn't quite enough sometimes :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Well maybe you can respond to something I was told recently, that didn't make sense to me.  A furnace repair guy told me that our furnace is way bigger than we needed, and that having some registers closed (in unused rooms) will shorten its life by making it work harder. I'm wondering if that's true.  ???

Posted by Joetta Fort, Independent Broker, Homes Denver to Boulder (The DiGiorgio Group) almost 6 years ago

Joetta, basically all that the furnace being "too big" will do is making it run for shorter periods of time.  This will mean that it will go on and off more often which is harder on the equipment---supposedly.  Closing off registers amounts, to some degree, the same thing as my piece of plywood does by cutting off the air circulation all together.  However I question as to how much real effect it will have on circulation through the heat exchanger if only one or two registers are closed---it will still be getting quite a bit through the others.  It will NOT make the furnace work "harder"---maybe longer and maybe shorten its life---but not harder.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Thank you - that makes a lot more sense!  Have a Merry Christmas!

Posted by Joetta Fort, Independent Broker, Homes Denver to Boulder (The DiGiorgio Group) almost 6 years ago

Always good to replace the air filters to keep the air moving through the system.  great expalination of why the air flow becomes restricted.

Posted by Rob Renk, AE | Fast Fix/Flip Loans for Residential Investors (Center Street Lending) almost 6 years ago

Joetta, you have a great holidays too

Rob, thanks

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 6 years ago

Good Post

Posted by Roger Pearson Crye, Leike Florence AL (Crye-Leike Florence Branch) almost 6 years ago

Participate