I think I'm having a humidity problem in my house. Before making any changes, like installing a whole house humidifier, I'm trying to collect data. Here is what I have so far.

Background
My house is a Cape Cod style home with an attic that was converted to a second floor. My home is located in southern New York in zone 5a. The main floor is insulated with R13 batts and upstairs is insulated with Icynene open-cell spray foam. I have a Goodman high efficiency, forced hot air furnace with one zone that heats both floors. The furnace is seven years old. Usually both floors are heated to within two degrees of each other.

Every window was upgraded to double-pane Anderson 400 series seven years ago. With the exception of the unfinished basement with drafty windows, the rest of the house is sealed up pretty tight. The only time we ever see condensation on the windows is when we take a shower or we are boiling water in the kitchen. The only windows that will show a small amount of condensation are the windows in those rooms.

I suffer from sinus problems, but those issues extend back prior to us buying this house. My wife feels fine. My 4-year-old daughter doesn't know any better, but she is in good health.

Data
Indoor temperature and humidity data was collected using Acurite digital indoor thermometers purchased from a big-box store about 4 years ago. I have two thermometers so I can compare the temps on both floors, apples to apples.

Indoor humidity usually stays in the 20s. It drops as low as 16%, when the furnace kicks on after we've been at work all day. When the furnace has been set to 60 degrees all day and then goes to 68 degrees at 4:00, this is the only time I see a big difference between the upstairs and downstairs temps. When this happens, the upstairs temps can climb to 76 degrees. If it's raining outside, I've seen the indoor humidity reach 48%.

Based on what I've read online, comfortable indoor humidity should be around 40% during the winter. With numbers as low as 16% in my daughter's room, we have been using a cool mist humidifier to keep the levels around 35% at night.

What is really confusing me are the numbers I'm seeing tonight:

Daughter's room w/o humidifier
Temp: 68 degrees
Humidity: 16%

Daughter's room after humidifier turned on
Temp: 68 degrees
Humidity: 35%

Outside data with Acurite indoor thermometer
Temp: 27 degrees
Humidity: 16%

WeatherBug App
Temp: 19 degrees
Humidity: 86%
Dew point: 15 degrees

Weather.gov
Temp: 23 degrees
Humidity: 68%
Dew point: 14 degrees

I don't understand why there are such differences in the humidity readings. Based on the data I've collected, do you guys think I need to install a humidifier? If so, what type would you recommend and why? I really want to get this right, especially because I don't want anything to happen to my daughter.

Thanks.

Look into Aprilaire humidifiers.

I don't trust either 86% or 68% for outdoors at those temps! Good grief. Was it misting, foggy, anything in the air? Cold winter air is usually dry unless obviously not.

I don't know anything about whole house ones. My present house in CT had one, but someone disconnected it. Don't blame them - I fear mold more than dry air. And in a rural area, who knows what dead critters and bugs might be involved?

I have a little 1 qt cool mist one (Holmes) by my desk and it's bad enough that I have to bleach and clean and replace filters. I don't sleep with it on. I breathe into my comforter, and figure the moisture in my breath moisturizes the air I inhale. Maybe dumb, but I have NEVER been happy with ANY humidifier, cool or otherwise.

I also spend a lot of the day next to a big window full of plants, and they need a lot of water.

For a while I used a $6 immersion coil in a stainless steel pot of water, and filled it as soon as the level dropped an inch. It burned up and it was a pain anyway, but NO MOLD! They ALL get moldy much too easily.

My advice? Turn heat down for sleeping. No misting then. No dusty rugs or curtains or bedding. In daytime, run one or two small cool mist ones and keep them CLEAN.

If you feel you must have a humidifier, I much prefer the stand alone types. I've seen way too many furnaces ruined by humidifiers.

Thank you for the responses. Since I first posted this question, I have also noticed that the main floor humidity is better off than upstairs. The main floor has been around 30% for the past few days. It seems like upstairs drops to 16% when the furnace first wakes up before we get home from work. Even though the thermostat is set to 68, upstairs reaches 75 degrees. That must be a big reason the air is drying out so much.

I have been thinking about putting upstairs on its own zone. Over the weekend, when the furnace doesn't turn off during the day, the upstairs and downstairs temps are very balanced. But it's that initial surge before we get home that is complicating things. Hopefully a second zone will keep the temperature more even and help with the humidity levels, too.

In the meantime, I am going to try and just run the humidifier for a couple hours before my daughter goes to bed. I will do as you guys suggest and stick with a portable humidifier. Thanks again... Logan

Not to burst your bubble but I've never seen a zoned warm air system which worked well. One thing you have to remember is when the furnace fires it runs at full capacity. That being said, all that heat has to go somewhere or you will over heat the furnace.

I have 3 zones, but my house was built in such a way that I can pretty easily heat just the main one.