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  1. #1
    Join Date
    Jul 2003
    Location
    Philadelphia Pa.
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    461

    Will lower blower speed save on Gas costs?

    I’m looking to save some money this heating season and one thing I was thinking about doing was having the blower speed set to low. I have a Trane xv80 with variable speed blower. I keep the blower set to “on” during the times we are home which keeps the air circulating at a lower speed all the time. The speed is currently set to mid-low.

    If the speed gets reduced to low I think the heat output temperature will increase, but will this increase or decrease the amount of gas that will be used? What about electricity - will there be a meaningful cost decrease on low speed?

    When I am away during the day( approx 8 hours) I have the temperature lowered and the blower off. If keep the blower on during this away time, will this keep the house warmer so that the recovery period will be easier?

    Thanks in advance for ideas about this.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,418
    Slower blower speed could very slightly increase gas use. Could result in a tad less heat put into the house and slightly warmer flue gases. Probably not enough to notice though.

  3. #3
    Join Date
    Feb 2007
    Location
    Las Vegas,NV
    Posts
    739
    You probably wont save a dime but if you do, set the savings aside for a new heat exchanger.


    All kidding aside, I would think it would take longer to heat the house thereby using more gas.

  4. #4
    Join Date
    Aug 2004
    Location
    Minnesota
    Posts
    349
    You dont want to lower your fan speed. Your furnace needs to get rid of the heat that is produced, and lowering the fan will only send more of it out of the chimney.
    White Bear Township, Minnesota
    www.summitheating.com

  5. #5
    Join Date
    Feb 2005
    Location
    In a van by the river
    Posts
    618
    I'd measure temperature rise and compare to data plate. From that point on that shoul tell you where you stand on fan speed... Assuming everything else is at proper settings.
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,826
    For every given structure/house, there is a Btu loss for each outdoor temperature. Nothing you can do with your furnace can change the loss from the house but some things you can do to your furnace could preclude it from delivering enough Btu's to offset the losses, leading to a decrease in room temperature. If your furnace was sized properly for your home, then you need to understand that the flame will burn during each cycle, just long enough to satisfy the heat loss from the home, meaning the thermostat reaches set-point. The true savings comes in selecting the most efficient furnace to begin with. If you burn a therm of gas (roughly 1,000 cubic feet) you're going to get 800 cubic feet of gas converted directly to heat for your home and 200 cubic feet of gas are paid for but lost in the combustion process. If you have a 95% furnace, theoretically only 50 cubic feet are lost. You may also be in an area or operating a prices that would make a dual fuel system attractive to save money on the gas bill. But you might as well face the facts, you've got to make investments, in energy conservation, that will pay dividends in the long term but monkeying with your existing furnace is not the way to accomplish it.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  7. #7
    Join Date
    Jul 2003
    Location
    Philadelphia Pa.
    Posts
    461
    Quote Originally Posted by skippedover View Post
    For every given structure/house, there is a Btu loss for each outdoor temperature. Nothing you can do with your furnace can change the loss from the house but some things you can do to your furnace could preclude it from delivering enough Btu's to offset the losses, leading to a decrease in room temperature. If your furnace was sized properly for your home, then you need to understand that the flame will burn during each cycle, just long enough to satisfy the heat loss from the home, meaning the thermostat reaches set-point. The true savings comes in selecting the most efficient furnace to begin with. If you burn a therm of gas (roughly 1,000 cubic feet) you're going to get 800 cubic feet of gas converted directly to heat for your home and 200 cubic feet of gas are paid for but lost in the combustion process. If you have a 95% furnace, theoretically only 50 cubic feet are lost. You may also be in an area or operating a prices that would make a dual fuel system attractive to save money on the gas bill. But you might as well face the facts, you've got to make investments, in energy conservation, that will pay dividends in the long term but monkeying with your existing furnace is not the way to accomplish it.
    Thanks to all that have replied. I am on board with what you are saying so will not ask to have the speed lowered. The house is very comfortable as it is. Moving to a 95% furnance is not possible now, and there would be issues with venting, and this furnace is six years old and has never given me a problem.

    Dual fuel may be the way in the future when I replace the A/C maybe a heatpump. Ac was installed along with furnance so both under warranty. I think my cost per therm is $1.81 due to increase 20% this fall, and my electric rate is between .13 and .15 cents per Kwh, due to increase 10% next year so perhaps in the end the type of fuel will not matter.

    What are your thoughts about leaving the vs blower on while away from home - will that help anything related to reheating the house during the recovery period or keeping all floors consistent, or will it just blow cold air around?

  8. #8
    Join Date
    Jul 2003
    Location
    Philadelphia Pa.
    Posts
    461
    Quote Originally Posted by summit View Post
    You dont want to lower your fan speed. Your furnace needs to get rid of the heat that is produced, and lowering the fan will only send more of it out of the chimney.
    So are there any downsides to increasing the speed? Will this send more heat into the house?

  9. #9
    Join Date
    Nov 2004
    Location
    Austin, TX
    Posts
    861
    There is an optimal speed for the blower for heating.
    Any higher and the heat will not transfer to the air optimally.
    This will result in more heat going up the gas flue and your heating bill going up.
    Any lower and it will result in not enough air, at a low enough speed the heat exchanger overheating and cracking.

    Generally, dinking around with your fan speed without having the tools to actually measure the effects of your changes will reduce the efficiency of the system.
    Last edited by allan38; 09-20-2008 at 11:39 PM.
    “I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.”
    ― Benjamin Franklin

  10. #10
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,701
    Changing the fan speed up or down will not change the heat output of the furnace. It only changes the temperature of the supply air. Speed up the fan and you have a larger flow of cooler air. Slow down the flow and you have smaller flow of warmer air. In both cases supplying the same amount of heat to the space.

    As someone said before if you slow the fan too much the temperature on the furnace will rise possible causing less life on the heat exchanger.
    It's not the Brand with the fewest repairs-It's all in the install!!! Attention to detail and using the best materials!

  11. #11
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The furnace has a temperature rise range it is designed to operate in, usually something along the lines of 35-65 degree range.
    For best efficiency it is generally best to have the airflow set so the temperature rise is near the lower end of the range.
    More air across the heat exchanger results in slightly more efficient heat transfer because the average difference in temperature between the heat exchanger and air will be higher than with lower airflow and a higher temperature rise.

    The bottom line is, if maximum efficiency is your concern, don't reduce the blower speed, unless the furnace already has to low of a temperature rise per the manufacturers specs.
    If more government is the answer, then it's a really stupid question.

  12. #12
    Join Date
    Jul 2003
    Location
    Philadelphia Pa.
    Posts
    461
    Quote Originally Posted by mark beiser View Post
    The furnace has a temperature rise range it is designed to operate in, usually something along the lines of 35-65 degree range.
    For best efficiency it is generally best to have the airflow set so the temperature rise is near the lower end of the range.
    More air across the heat exchanger results in slightly more efficient heat transfer because the average difference in temperature between the heat exchanger and air will be higher than with lower airflow and a higher temperature rise.

    The bottom line is, if maximum efficiency is your concern, don't reduce the blower speed, unless the furnace already has to low of a temperature rise per the manufacturers specs.
    Thanks Mark

    I am totally comfortable with the heat coming out of the unit although I know that doesn't mean it is correct, but this is how my contractor set it up. In mild cold weather air from the registers is about 96F to 98F. In colder weather it is about 108F( maybe a longer run time) and if second stage is used it is around >115F so no problem - so I will leave the blower speed as is.

    Any thoughts about the other part of my question regarding leaving the fan circulating while no one is home?

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    66,820
    Quote Originally Posted by jerrod6 View Post

    Dual fuel may be the way in the future when I replace the A/C maybe a heatpump. Ac was installed along with furnance so both under warranty. I think my cost per therm is $1.81 due to increase 20% this fall, and my electric rate is between .13 and .15 cents per Kwh, due to increase 10% next year so perhaps in the end the type of fuel will not matter.

    ?
    Did you op to pay early for the rate hikes? So you don't see a sudden increase in 2010.
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