# Thread: kwh consumption of humidifer in hvac system

1. Originally Posted by mishman
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.
It comes down to, you have a steam humidifier that has run for two years without service. I guarantee you that it is loaded with deposit. Loaded with deposit, the humidifier will still come on and pull the same amps, but not produce even half the rated capacity.

Have a contractor come out and pull the bucket and you will see what I'm talking about.

2. Originally Posted by skizot
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.
Thanks for pointing out my errors. You are right. .2 ACH is an air change in 5 hours. That is 5 air changes in 24 hours or 15 lbs. of moisture per day.
There a couple other errors here also. A leaky home would have an air change in a couple hours. 1440 watts at 100% eff. will evaporate 4 lbs. of water. My guess is that with radient cabinet heat loses, 66% of the heat goes to evaporate water. One lb. of water takes 1,050 btus of heat to evaporate. So maybe 3 lbs. of humidification for 1.4 kw. per hour. This is 5 X 1.4 kw X \$.10/kw X 30 day = \$21 per month if the home has .2 ACH.

If the home has .4 ach double that or \$42/month. Thanks for straighting me out the details. The fact remains, low occupancy homes need some humidification.

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Originally Posted by teddy bear
Thanks for pointing out my errors. You are right. .2 ACH is an air change in 5 hours. That is 5 air changes in 24 hours or 15 lbs. of moisture per day.
There a couple other errors here also. A leaky home would have an air change in a couple hours. 1440 watts at 100% eff. will evaporate 4 lbs. of water. My guess is that with radient cabinet heat loses, 66% of the heat goes to evaporate water. One lb. of water takes 1,050 btus of heat to evaporate. So maybe 3 lbs. of humidification for 1.4 kw. per hour. This is 5 X 1.4 kw X \$.10/kw X 30 day = \$21 per month if the home has .2 ACH.

If the home has .4 ach double that or \$42/month. Thanks for straighting me out the details. The fact remains, low occupancy homes need some humidification.
No problem. After reading ascj's post, I bet he's hit it on the head if the house is, indeed, as tight as the OP says. It is unclear whether the OP just had the humidifier installed this Winter, or if he's had it this whole time, and just this season his electrical usage has spiked. If it's the former, then that still leads me to believe that the house is not as tight as believed. Maybe he can clear that part up for us.

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