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Q. I have two heat pumps in my home. The larger is used to take care of the main living area and smaller for the sleeping area. The house is a single level Rancher. The smaller unit has a steam humidifier installed in the air handler just below the filte r in the base of the unit. The humidistat is installed in the cold air return at the air handler which is in the basement. I am told this is the proper place to monitor and sense the true humidity level coming from the rooms. The humidity level adjustmen t on this control is very sensitive. The slightest adjustment and the relative humidity can swing from 25 to 50 percent which can make it pretty wet in the house. I have questioned my service provider who installed the system and humidifier about this an d also whether the humidistat should be located upstairs. He says this is the proper operation and location for the control in order to set the true humidity level. I would appreciate your view on this question.
A. We have a few months around here when the outside air temperature gets low and when that air filters into the house and we heat it up to tolerable indoor temperatures it is and feels very dry. This air is so dry it causes our skin to get dry and itchy and we collect static electricity that creates those annoying little sparks when we reach for a doorknob, light switch or even another person. The whole notion of introducing moisture into our indoor air isn’t a new idea but in may ways only recently ha s it begun to be fully understood, even by the professionals. I am well known around here for harboring negative feelings towards humidifiers in general after seeing decades of problems associated with their use.
Your experience of touchy controls probably has more to do with with the accuracy of the controls themselves along with the probability that the steam orifice inside of the unit may be getting clogged somewhat from mineral deposits left by the departing water, much like a showerhead that clogs up over time with a mineral build up.
The location of the humidifier’s sensing control, the humidistat, is where it is for a good reason. The control wants to sense the humidity in the air well after the system has had a chance to mix the added moisture well with the rest of the air inside the house and at the air return is probably the best location for that. If the sensing control was anywhere near a supply register it would likely sense a falsely elevated humidity level and reduce the moisture input accordingly.
Why I have had a long time quarrel with humidifiers comes down to a couple of well demonstrated downsides to their use. The first problem I have had with them is they can be breeding grounds for all sorts of human maladies. I was once inspecting a hous e for a medical doctor and when we got near the furnace I pointed to the drum and reservoir type humidifier hanging off the side of the heat duct and I asked the doc if he knew what that was. “A disease distribution system” was his prompt reply. The huma n illness connection to humidifiers was first identified in the early 1970s and was called “humidifier fever”. The good news is that after about 30 years of wondering what to do about this the industry finally came upon the bright idea of placing Ultra Violet C (UVC) sanitizer lights inside of the main duct that will kill 99.9 percent of the airborne microbials that pass it. At a cost of about $400. installed, problem number one is solved.
The second problem that I have with the notion of pumping moisture into the interior air is, as is happening with yours to a minor degree, when it gets out of whack and puts too much moisture into the air that moisture will find its way to somewhere out of your notice and condense. I have seen the underside of roofs that the owner thought was leaking slick with condensed moisture from a humidifier gone wild. One home owner thought I was crazy-- and said so-- after he showed me his wet attic and I asked to see the basement. I went down to the furnace, shut off the water supply to the humidifier and told him his attic would be dry in a day or so.
Your telling me the interior humidity ranges in your house tells me that you have a separate instrument (hygrometer) that tells you what the system is producing. Keep an eye on the humidity and don’t let it get above 50 percent in the house. Fifty perc ent and above is the range in which things can grow and get messy.
For those who don’t have humidifiers and get annoyed by those pesky static sparks, just spraying some of that anti-cling clothing spay on the carpets will greatly reduce the sparking.