I had an Aprilaire AA700M humidifier installed on my gas furnace last year. Everything worked fine from what I could tell. Fast forward to this winter, and the humidifier isn't keeping up with the humidity set point on the thermostat. I have an Ecobee 3 smart thermostat, and the desired humidity level is set to 38%.
I have a 3-story town house, approx 2000 sqft. In the past week or so, the humidity levels were over 40%, although it had been raining for a day or two at that time. It's been dry for roughly a week. Lows overnight have been into the mid-20s F and daytime highs in the mid-40s to low-50s F. Right now, the thermostat is reading 29% humidity in the house and 68F temperature, with an outside temperature of 55F and 18% humidity. Earlier in the winter when temperatures were down to 10F, humidity levels in the house were below 20%.
I would expect the Aprilaire 700 to be able to properly humidify a 2000 sqft house (its specs indicate it can humidify up to 5300 sqft), but I am not seeing that. The water panel was just changed at the beginning of the season. Is this normal, or is there something wrong with the humidifier or the install? The humidifier turns on and off when commanded (I can hear the solenoid click open and closed, and I can see and hear water draining through the drain line).
I previously had the Ecobee set to Frost Control for the humidifier, but the HVAC technician indicated that was a problem when the outside temperatures got too low (and the humidifier wouldn't turn on at all? Hard to tell exactly how Ecobee's Frost Control works from what I read online...).
The house was built around 2000, Northern Virginia in the US. It does not seem to be very "tight" - there's no separate vapor barrier that I can see (it may be part of the sheathing?), electrical outlets have foam gaskets but no sealant, windows are original and losing vacuum seals, etc.
I know the RH of air drops as you warm it (especially with a gas furnace) - my question is to what extent the humidifier should be able to counteract that effect.