How much difference does hot vs cold air make with regards to an Aprilaire 600 furnace humidifier evaporation rate

furnacehumidifierhumidity

If I run the humidifier only when the heat is on, I get good evaporation. However, I want to consider also running it with just the fan running because our furnace doesn't run all that often. Will I still achieve reasonable evaporation in this case?

Best Answer

I ran the following tests with an ambient temperature of approximately 70 degrees F. I measured the (hot) water flowing into the humidifier and the water flowing out of the drain to calculate the % evaporation in each case (there is a reasonable margin of error).

  1. Furnace running in low stage. Approximate air temperature coming from register is 120 degrees F. Humidity was 25% @ 70F. Measured 24% evaporation rate.

  2. Furnace is off, fan running on low setting. Approximate air tempertaure coming from register is 70 degrees F. Humidity was 25% @ 70F. Measured 19% evaporation rate.

  3. Same setup as 2, but humidity was ~32% @ 70F. Measured 14% evaporation rate.

Unfortunately, this indicates a large amount of water being wasted, especially with the heat off. Aprilaire advertises that it uses 3 gallons per hour with a 0.7 gallon/hour evaporation rate (24%), which matches with my test for #1.