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  1. #1

    kwh consumption of humidifer in hvac system

    We built a new house in NH - roughly 3,000 sq. ft.two years ago. It has a Boderus propane fired furnace with both radiant floor heating and forced hot air (through a heat exchanger). During the first heating season (year ago), builder noticed that the humidity was too low and wood was drying so he had the sub take out original humidifier and put in a new one. Sorry, I am not at house now and don't recall name of new unit.
    This new unit, installed in April last year, has worked well this heating season, however, our kwh consumption has been through the roof (up 2.5 times last year's winter months) (March 08 13 kwh/day vs. March 09 43/kwh/day. I used to work for an electric utility and have gone through the house carefully. We don't use the house in the winter but for an occasional winter weekend and house is set at 58 degrees. The only difference this winter from last is this new humidifier. It is attached to the heat exchanger and to the water system to supply water. Is it possible that a humidifier could use so much more power?

  2. #2
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    Depending type humidifier it is, yes, its possible.

    Is your water supplied by a well?
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  3. #3

    Well water supplied

    Yes, humidifier is supplied by well. Water is somewhat soft (leaves marks on glasses). Can it literally be responsible for 15-20 kwh/day consumption?

  4. #4
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    Quote Originally Posted by mishman View Post
    Yes, humidifier is supplied by well. Water is somewhat soft (leaves marks on glasses). Can it literally be responsible for 15-20 kwh/day consumption?
    I think it depends on what type of humidifier you have. The steam humidifiers by Honeywell use a lot of electricity. The 12 GPD model uses about 1440 watts when it's running. So, if it's running 24 hours a day, 7 days a week, then you'd have:

    (1440 / 1000) * 24 = 34.56 KWH / day from the humidifier alone.

    If you post more info about the humidifier like brand/model, I'm sure people could help out a little more.

  5. #5
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    Depends how drafty your house is, and what RH% you are maintaining in the house.

    Don't forget.
    Many standard humidifiers use 6 gallons an hour of water, to put gallon an hour into the air. So part of that electric bill, is also the water pump.

    6x24 = 144 gallons a day. Thats if it has to run 24/7 to maintain set humidity.
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  6. #6
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    I wonder if a water conserving drum type bypass humidifier with a inline water filter would be more economical to operate. You'd have the cost of the filters, but reduced water consumption.

  7. #7
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    Quote Originally Posted by mishman View Post
    We built a new house in NH - roughly 3,000 sq. ft.two years ago. It has a Boderus propane fired furnace with both radiant floor heating and forced hot air (through a heat exchanger). During the first heating season (year ago), builder noticed that the humidity was too low and wood was drying so he had the sub take out original humidifier and put in a new one. Sorry, I am not at house now and don't recall name of new unit.
    This new unit, installed in April last year, has worked well this heating season, however, our kwh consumption has been through the roof (up 2.5 times last year's winter months) (March 08 13 kwh/day vs. March 09 43/kwh/day. I used to work for an electric utility and have gone through the house carefully. We don't use the house in the winter but for an occasional winter weekend and house is set at 58 degrees. The only difference this winter from last is this new humidifier. It is attached to the heat exchanger and to the water system to supply water. Is it possible that a humidifier could use so much more power?

    If its a steam humidifir, then yes it can account for the electric. If it is a steamer and it was installed 2 years ago, then I hope it was pulled and cleaned at least every year. If it wasn't then it's probably full of deposit, not producing steam, running all the time, and still pulling major amps trying.

  8. #8

    more info on humidifier

    I have found out that the humidifier is a steam unit, high capacity, made by Honeywell. Humidity level was set at 32 by the builder of the house, who indicated that at that level, wood would not dry out during the heat season (and we have noticed a difference when we have been over there). While this is a year round house, it is largely unoccupied in the winter except for a weekend a month. The temperature is set at 59 degrees when we are not there and the house is well built and very tight.
    Does this type of humidifier need to be cleaned every year? Is that something a homeowner could do or does it require a technician?
    Thanks for the helpful feedback so far.

  9. #9
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    Quote Originally Posted by mishman View Post
    I have found out that the humidifier is a steam unit, high capacity, made by Honeywell. Humidity level was set at 32 by the builder of the house, who indicated that at that level, wood would not dry out during the heat season (and we have noticed a difference when we have been over there). While this is a year round house, it is largely unoccupied in the winter except for a weekend a month. The temperature is set at 59 degrees when we are not there and the house is well built and very tight.
    Does this type of humidifier need to be cleaned every year? Is that something a homeowner could do or does it require a technician?
    Thanks for the helpful feedback so far.
    Are you sure that the house is built very tight? Speaking from experience, you should never just take a builder's word on whether a house is tight, or not. The only way to determine that is with a blower door test. If your house is indeed tight, it should have no problems maintaining 32% humidity at 59 degrees, even without any occupants.

    20 KWH / day = (1440 / 1000) * x
    x = 200 / 14.4
    x = 13.9

    So, if you're saying that your bill has gone up 20 KWH / day over what it used to be, then that means the humidifier is running 13.9 hours a day, every day. Even without any occupants, that seems like a really long time to run in order to maintain 32% humidity at 59 degrees in a "very tight" home. I would suggest getting a blower door test done.

  10. #10
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    Quote Originally Posted by skizot View Post
    Are you sure that the house is built very tight? Speaking from experience, you should never just take a builder's word on whether a house is tight, or not. The only way to determine that is with a blower door test. If your house is indeed tight, it should have no problems maintaining 32% humidity at 59 degrees, even without any occupants.

    20 KWH / day = (1440 / 1000) * x
    x = 200 / 14.4
    x = 13.9

    So, if you're saying that your bill has gone up 20 KWH / day over what it used to be, then that means the humidifier is running 13.9 hours a day, every day. Even without any occupants, that seems like a really long time to run in order to maintain 32% humidity at 59 degrees in a "very tight" home. I would suggest getting a blower door test done.
    A misconception-- Where does a home get moisture from when people are not in the home? A tight home will have an air change every 5 hours (.2 ACH). Typical homes may have an air change every 4-5 hours. The air outside is 20^F, 60%-70% RH, 10 grains of moisture per lb. of air.
    Keeping a home at 58^F, 30%RH, 20 grains requires 10 grains of moisture per lb. of air passing through the home. A 3,000 sqft. home has 27,000 FT^3 of air that changes every 10 hours (.2 ACH). There is 13 ft.^3 of air in a lb. of air. 27,000 FT^3 / 13 FT.^3 X 10 grains/lb = 3 lbs. of moisture removed every air change or 5 hours, .2ACH tight. This home needs 25 lbs. of moisture everyday to maintain 30%RH. Thats provided that the home is air tight. In fact this home should have mechanical fresh air ventilation when occupied to purge indoor pollutants. Fresh air ventilation is particularly important during the mild weather.
    A lot of numbers but what is important is that the number of occupants and the total hours per day they are in the home is critical. Occupants and their activities are the humidifiers. During cold weather, the air flowing through the home is the dehumidifier. During cold weather, an adequately ventilated home will need humidification unless you have many occupants. During wet warm weather, adequate fresh air ventilation, and normal occupancy, you need dehumidification. Most heating/cooling contractors do not understand the finer points of this concept. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  11. #11
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    Quote Originally Posted by teddy bear View Post
    A misconception-- Where does a home get moisture from when people are not in the home? A tight home will have an air change every 5 hours (.2 ACH). Typical homes may have an air change every 4-5 hours. The air outside is 20^F, 60%-70% RH, 10 grains of moisture per lb. of air.
    Keeping a home at 58^F, 30%RH, 20 grains requires 10 grains of moisture per lb. of air passing through the home. A 3,000 sqft. home has 27,000 FT^3 of air that changes every 10 hours (.2 ACH). There is 13 ft.^3 of air in a lb. of air. 27,000 FT^3 / 13 FT.^3 X 10 grains/lb = 3 lbs. of moisture removed every air change or 5 hours, .2ACH tight. This home needs 25 lbs. of moisture everyday to maintain 30%RH. Thats provided that the home is air tight. In fact this home should have mechanical fresh air ventilation when occupied to purge indoor pollutants. Fresh air ventilation is particularly important during the mild weather.
    A lot of numbers but what is important is that the number of occupants and the total hours per day they are in the home is critical. Occupants and their activities are the humidifiers. During cold weather, the air flowing through the home is the dehumidifier. During cold weather, an adequately ventilated home will need humidification unless you have many occupants. During wet warm weather, adequate fresh air ventilation, and normal occupancy, you need dehumidification. Most heating/cooling contractors do not understand the finer points of this concept. Regards TB
    No one ever stated that a humidifier is not necessary. What was stated is that amount of time a 12 GPD steam humidifier is required to run to supply 32% RH at 59 *F with no occupants. With all that you know, mathematically, can you now show how long the 12 GPD steam humidifier should be running to supply that 25 lbs. of moisture per day? That is what's in question here.

  12. #12
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    Quote Originally Posted by teddy bear View Post
    A misconception-- Where does a home get moisture from when people are not in the home? A tight home will have an air change every 5 hours (.2 ACH). Typical homes may have an air change every 4-5 hours. The air outside is 20^F, 60%-70% RH, 10 grains of moisture per lb. of air.
    Keeping a home at 58^F, 30%RH, 20 grains requires 10 grains of moisture per lb. of air passing through the home. A 3,000 sqft. home has 27,000 FT^3 of air that changes every 10 hours (.2 ACH). There is 13 ft.^3 of air in a lb. of air. 27,000 FT^3 / 13 FT.^3 X 10 grains/lb = 3 lbs. of moisture removed every air change or 5 hours, .2ACH tight. This home needs 25 lbs. of moisture everyday to maintain 30%RH. Thats provided that the home is air tight. In fact this home should have mechanical fresh air ventilation when occupied to purge indoor pollutants. Fresh air ventilation is particularly important during the mild weather.
    A lot of numbers but what is important is that the number of occupants and the total hours per day they are in the home is critical. Occupants and their activities are the humidifiers. During cold weather, the air flowing through the home is the dehumidifier. During cold weather, an adequately ventilated home will need humidification unless you have many occupants. During wet warm weather, adequate fresh air ventilation, and normal occupancy, you need dehumidification. Most heating/cooling contractors do not understand the finer points of this concept. Regards TB
    Looking at your numbers further, I see that they are incorrect.

    1. 0.2 ACH = an air change every 5 hours, not 10.
    2. If 3 lbs of water is lost every air change, then the house will not need 25 lbs. of water added per day, it will need 14.4 lbs. of moisture added per day. This can easily be calculated as (24 [hours in a day] / 5 [an air change every 5 hours]) = 4.8 * 3 = 14.4 lbs of water or 24 [hours in a day] * 0.2 [ACH] = 4.8 * 3 = 14.4 lbs of water. This only holds true if your 3 lbs. per air change figure is, indeed, correct.

    So, the OP says he has a high capacity Honeywell TrueSteam humidifier, which would be the 12 gallon per day model. This is what Honeywell lists as the capacity. For the TrueSteam, the listed capacities are based on a 1:1 humidification delivery rate. So, given that, you have the following:

    1 gallon of water = 8.35 lbs
    12 gallons of water per day = 12 * 8.35 = 100.2 lbs per 24 hours
    This yields 100.2 / 24 = 4.175 lbs per hour delivery rate.

    Since 14.4 lbs of water is needed per day, the humidifier should only be running:
    14.4 / 4.175 = 3.45 hours

    The 12 GPD model pulls 12 Amps. So, to get the watts consumed, you have:

    120 * 12 = 1440 watts, or 1.44 KWH.

    If it runs for a total of 3.45 hours a day, you have:

    1.44 * 3.45 = 4.968 KWH / day.

    Note that the 4.968 KWH / day does not take into consideration the power used by the blower motor, but that will be negligible compared to the power used by the coil in the humidifier.

    So, since the OP says his bill has increased by about 15-20 KWH / day, I'd say that it's running a lot more than 3.45 hours a day, which means that his house is most likely not as tight as was previously though.

    Note the both of our numbers are based on the Natural ACH, which obviously goes out the window when you have a windy day. The air changed in from the outside is assumed to have 0 grains of water vapor in your figures, teddy bear. Although the content of moisture in the air when it is cold outside is very small, it is still something to factor in.

  13. #13
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    http://www.eia.doe.gov/emeu/consumpt...on_tables.html
    With your occasional use you're below 95% of all households, so I guess your HDD and so on have to be factored in.
    Maybe some other electrical device is failing.
    Could also be a PoCo "mistake".

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