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  1. #1

    Can a restrictive air filter force the furnace to use more gas?

    Can a restrictive air filter force the furnace to use more gas?

    My furnace was installed Dec 14th and my first bill was below 100.00 mark.
    My next bill was over double. Now mind you its normally colder in Jan then Dec around here (NJ).
    My last bill for Feb dropped over 40.00 from Jan. All meter reads were done by me. The temp is on hold (71)
    Bryant 90I 80,000 BTU.

    When the furnace was first installed, they had the el cheapo 1 inch fiberglass filter. Sometime in Jan I switched to a 3m 1 inch 600 rated.
    Once my filter box was resized correctly I was able to put in a Merv 12 4 inch filter which was in Feb.

    So basically Im thinking the 3m filter forced the furnace to use more gas. I know that a restrictive filter can use more electric because the Evolution will kick the fan up higher to meet the right CFMs. Im just not sure how to explain how it would use more gas.

    Thanks!

    Bret

  2. #2
    Join Date
    Feb 2008
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    restirictve airflow will cause a number of issues. more gas consumtion, sure, system has to run longer to satisfy your cold feet its also very bad for your heat exchanger. air filter, less than $50 fix for a hugemongus repair!!!

    you've only been running it three months. i wouldn't say thats enough time to see how efficient this furnce is. any change in the gas prices? did you figure that inot the difference? find efficiency by looking at your gas bill, meter, is way inaccurate
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  3. #3
    Join Date
    Jan 2004
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    Yes, it can cause higher heating bills.
    Especially if your ductwork is in an unconditioned space.
    The air moves slower, losing more of its heat to the unconditioned space.

    As the heat exchanger gets hotter, the furnace becomes less efficient because the flue gases in the secondary heat exchanger are too to allow any condensing and releasing of latent heat. So you could lose as much as 10 to 15% efficiency.
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  4. #4
    Join Date
    Feb 2004
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    Filters can make a difference as was explained above. Look at your gas bill it should tell you how much you use, the cost, and also degree days...shows how the temperature will very between months.
    Before you criticize someone, walk a mile in their shoes...that way you are a mile from them and have their shoes

  5. #5
    Join Date
    Sep 2002
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    Quote Originally Posted by twisterbret View Post
    ...the Evolution will kick the fan up higher to meet the right CFMs. Im just not sure how to explain how it would use more gas.

    Thanks!

    Bret
    Provided that the ecm ramps up enough to make up for the restrictive filter, gas consumption per heating degree day should have remained the same.

    Insufficient airflow = higher gas consumption
    ECM ramping up to maintain airflow across restrictive filter = higher electricity consumption.

  6. #6
    Join Date
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    That 3m most likely was restrictive enough that the ECM was not able to maintain CFM.
    It don't take long for filters to cut back air flow even with a VS blower.
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  7. #7
    Join Date
    Oct 2003
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    What were your degree days (degree days = hours outdoor temps below 65) for those months.

  8. #8
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    Quote Originally Posted by bzzline View Post
    What were your degree days (degree days = hours outdoor temps below 65) for those months.
    Heating dgree day is the average temp under 65 for 24 hours.
    Cooling above 65.
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  9. #9
    Join Date
    Feb 2003
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    Huntsville,AL
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    the number of days in a billing period varries here from 27-33.

    compute your cu-ft gas/degree-days

    DD= 65- (hi - lo)/2 = 65- average outdoor temp.

    know that the DD quoted on your bill may be slightly different than what you measure --
    & DD needs to be for the billing period, not calendar month --
    my meter is read between 19th & 24th.
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  10. #10
    Join Date
    Oct 2003
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    Valdosta Ga
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    Thank you for the corrections

  11. #11
    Quote Originally Posted by hetrola View Post
    Filters can make a difference as was explained above. Look at your gas bill it should tell you how much you use, the cost, and also degree days...shows how the temperature will very between months.
    I'm not sure how Degree Day works but it was
    (Feb 703)(167.00) Therms 111.44
    (Jan 683 209.00) Therms 143.11
    The online bill states the bills should have gone up 3.00 for because the delivery charge went up.

    I don't think Feb was all that much warmer then Jan. I'm going to have to blame the filter and keep and eye on it. The 3m filter used was not their highest rated, it's 600 for "high Velocity" equipment. It was pretty darn dirty have 30 days of use. I'm happy how the 4 inch filter is working. Even if I change it 3 times a year it's helping with dust and still allowing the furnace to breath. I'm working on some infiltrations issues but the dogs and cat have to stay. I will say it never did smell like "Pet" when you walked in.

  12. #12
    The "more restrictive" filter you used is not going to cause this large of a fluctuation in your gas bill. In tests we have done the Filtrete 600 has a pressure drop of 0.24" wg at 400 fpm. I don't know what 4" MERV 12 filter you are using but I would suspect it has a pressure drop of at least 0.19" wg. You might see a 10% to 15% increase but that is about it. As others have suggested you will have to look elsewhere for the answer to the increase. Colder temperatures outside. Fires in your fireplace. More activity from your family and pets (doors opening and closing). All are possibilities and there are more.

    But you are on the right track. The 4" filter box is the way to go. Lower pressure drop and higher efficiency.

  13. #13
    Join Date
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    Filtrete 600 has a pressure drop of 0.24" wg at 400 fpm.

    Your assuming his return velocity is only 400FPM.

    Did you test the air filter at 800 FPM. and higher.

    We don't know what his return duct design is.
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