Flow through-humidifiers are replacing the older drum humidifiers in recent years. This is mainly due to tighter houses. The disadvantage to a drum is that standing water present in the reservoir allows bacteria to grow. Because of our more closed homes, the bacteria stay inside the house for the winter and keep re-circulating those bacteria.
The flow-through humidifier has no water sitting until the next time it calls for heat. Water is spread down the pad evenly. Some of the furnace air passes through the water-soaked pad and carries that moisture into the heating system to be distributed throughout your home.
The advantage of the drum style is you need no drain as the water sits in the reservoir. The downside to the flow through is there is a greater cost of operation due to the water that drains through the pad.
The reported labor cost to install a flow through furnace humidifier is between $150 and $200. Additional parts may be $10 – $50.
Here’s how you could do it yourself.
1. Turn off power to the furnace and remove the old humidifier if present and isolate the water lines, wiring and ducts.
2. Use the template to level and trace the opening to be cut in the cold air return.
3. Cut the template-traced hole in the duct work with your tin snips.
4. Mount the humidifier case with sheet metal screws. Mount the unit on the return air duct whenever possible. You can mount to the supply side, but the system works much better on the return side and poses less of a threat to your furnace involving water and electrical components.
5. Connect the water source to the casing.
6. Connect the wiring for the humidistat, transformer and solenoid with wire nuts.
7. Install the bypass duct pipe from the unit to the warm air duct work. Remember, the shorter and straighter the bypass, the better. Check that the damper can swing freely. If it’s summer, close the damper. If it’s winter, leave it open.
8. Install the drain piping. If there isn’t a drain, run PVC piping to the laundry drain, or use a condensate pump to move the water to a drain, wash tube or outside.
9. Test the cycle. Install the flow through pad, turn on the furnace power and water, switch the humidistat to high and check for leaks. Depending where you live, set the humidistat to 35-45%. It may take 4-5 days for your house to adjust. If the windows or surfaces feel damp, the level is too high, causing wood to absorb humidity and ice to form on windows. But if static is still present, then the air is too dry.
Change the pad once a year.