2008-02-09, 10:14 AM
Just had a furnace humidifier installed yesterday and have the humidistat cranked up to almost as far as it will go. Humidity level in the house is still only 30. I notice the humidistat is located only about 6 inches above the unit. Could this be the reason I can't bring the humidity level up higher? Thanks
2008-02-09, 10:44 AM
I recently installed a humidifier myself and the instructions specifically said to install humidistat a minimum of 6 inches above the top of humidifier, so I'm guessing your install is OK. My humidistat is about 7 inches above, and mine won't go above 30% either. However, it is a tremendous improvement when compared to no humidifier. Cheers.
I was never a fan of putting the humidity control in the cold air return, but that's the way it's apparently recommended. Perhaps this keeps the humidity in the house at a manageable level, preventing mold, mildew, etc.
One must remember that the relative humidity is dependent on temperature - I don't remember the exact ratio any more, but air can hold much more moisture at a higher temperature than at a lower one, therefore, the cold air return has a higher relative humidity than the warmest part of your house does.
2008-02-09, 12:09 PM
Before you blame the installation location, see if the humidistat is getting a reasonably accurate reading from its present location. If it's the mechanical kind like mine, it will make an audible 'click' when it turns on/off. If that's happening around the 30% mark on the dial and you've turned the humidistat up to 100%, then the humidistat is fine, your humidifier just can't keep up.
Power to a humidifier usually comes from the furnace fan circuit since there's no point in running water to the humidifier without airflow. If your furnace isn't running very often, the humidifier doesn't get enough time to do its thing. If you can turn your furnace fan on manually via the "fan" switch on your thermostat or the manual override on the furnaces fan controller, try letting the fan run for a day or two and see if the humidity climbs much.
I keep my furnace fan running on low speed all of the time and I've also got my humidifier fed with hot water rather than cold - it seems to evaporate better when just the low speed fan is running and circulating room-temperature air. I have no trouble keeping 30-35% humidity in a big house with a General 1042L humidifier, but it does take a day or two to hit the set point when I first turn the humidifier on at the start of heating season.
2008-02-09, 12:37 PM
I had a similar problem when I installed a General Aire Humidifier. The humidistat was installed just as you had done and it was reading the humidified air from the unit. I guess because it was too close. I had to move the humidistat and install it on the main return air duct more than six feet away from the furnace unit itself. That has been working ok for years now.
First ensure that the humidistat works as noted by the post above. Then relocate the unit as far away as you can on the return air so that it is seeing an unmixed return air.
If your furnace isn't running very often, the humidifier doesn't get enough time to do its thing.True, but if the furnace isn't running much, it's probably warm enough that additional humidity is not required, so it's a bit "self correcting".