I recently had a flow through humidifier professionally installed but I am disappointed with its performance. Even when the humidistat is turned to max it can't get the humidity in the house above 30%. The water supply is drawn from my well, not city water, and is very cold coming into the house. Is it possible that the water is too cold as it passes through the humidifier, and doesn't have an opportunity to vaporize?
What model of humidifier is it and how many sq ft is your house? Is the humidifier installed on the supply or return, and if it's on the return is the humidistat installed at least 12" above the humidifier? Is the bypass damper open?
Are you sure the unit is working, can you see it draining water after a few minutes? Some humidifiers are wired so that they only come on when the furnace is heating. You could have it wired to run anytime the humidistat is on. Some people run other heat sources like fireplaces that prevent the furnace and humidifier from running as much.
Do you have an HRV that might be running continuously?
Supplying hot water to the humidifier would speed up the evaporation process, but you should upgrade the 1/4" water line to copper if the existing water line is plastic. If you have a hot water tank I would make sure the temperature is at least 140F so that the humidifier isin't being supplied with bacteria. You would need to have an anti scald valve installed to lower the hot water temperature at the faucets.
Do you have a heat pump? The best humidifier I've found is the Aprilaire 800. You don't waste water down the drain, and if wired to a 240 volt circuit it will put out a lot more humidity.
It's a General Air 1042, installed in a house that is approx. 2500 sq ft, 4 level back-split. It is installed on the return side, and I believe the humidistat is at least 12" above the humidifier.
The water is certainly running through it, as it drains into my sump pit and is easy to see. I believe it is wired to run only when the furnace kicks on. We do have a gas fireplace but we only turn it on occasionally.
I appreciate the extra info on the things to consider if I switch to supplying hot water, I never would have thought of that and I certainly don't want to be blowing bacteria all around the house.
No heat pump, forced air natural gas.
I attached the specs at the bottom of this post. Unless you have a loose house or ceilings higher than 8' that humidifier should have the capacity to maintain at least 40% RH. Being a 4 level split could be affecting things somehow. I've had to upgrade a few humidifiers with larger ones to solve problems like yours, it's possible you might just need a larger humidifier. The Aprilaire 800 Steam humidifier that was posted by ksefan looks like a great machine, but no doubt more costly than a bypass humidifier. The Generalaire 1099 is 23GPD and might be what you need to get 35 - 40% RH.
I would see if the installer would be willing to come back to take a look. He might be able to replace your humidifier pad and re-sell the humidifier and then look at getting you a larger model.
Thanks for the suggestion. I think I will follow your advice and ask the installer about upgrading to a larger model. Thanks for taking the time to look into this for me. :)