Posted on

What is the difference in a power humidifier, Aprilaire 700 and a by-pass humidifier such as the 550, 600, & 400?

Question: What is the difference in a power humidifier, Aprilaire 700 and a by-pass humidifier such as the 550, 600, & 400?

Answer: Depending on the square footage of your home, and cost would determine which humidifier you choose. If your home is over 2,000 square feet I would definitely go with the 700. If you have a smaller home under 2,000 square feet I would probably go with the 550, 600 or 400 humidifiers. My own personal opinion is that I like the power humidifier (700) over the by-pass humidifiers because with the bypass humidifier you are running humidified air across your filter, blower, heat exchanger and up through your furnace. The thought of having the moist air running up through your furnace just doesn’t make sense to me, but people having be using them for years with excellent humidification results. Also, make sure you have enough room for the humidifier. You should have at least 16″ between the furnace and a wall or obstruction to be able to install and service the humidifier. 16″ is the minimum. 24″ would be more preferable. The hole that you cut in the furnace duct work for the 700 is approximately 15″ square. If you do not understand the concepts of high and low voltage electrical wiring, some sheet metal work and plumbing work, then I would probably leave it to a professional. The humidifiers with the computerized humidistat (700,600, 400) require 6 low voltage wiring connections and one high voltage 110 volt connection. If you have a friend that understands wiring and how to read a diagram then maybe they could help? The Aprilaire humidifiers can turn off and on by using an A50 current sensing relay. If you have a newer furnace, with hook ups on the control board for humidifiers or electronic air cleaners, then you will not need the A50 relay. You can wire you humidifier to turn off and on using your furnace’s control board. You can tell whether or not you need the relay by looking at the board or looking and reading the furnace’s wiring schematic. The Aprilaire 700 humidifier has a transformer built in, to control the power fan relay and on off relay in the 700. The 550, 600, and 400 humidifiers come with a transformer that you can wire up. I always use the furnace’s existing transformer to power the humidistat. I run wires up to the humidistat off the “R” and “C” terminals on the furnace’s control board. If you decide to install the humidifier yourself, and you do not understand the wiring you can possibly burn the humidifier, humidistat, and your furnace controls up. This would void the humidifier’s warranty. I would recommend hiring someone if you are not familiar with the wiring. I believe you will really like the humidifier once it is installed and working for a few days. No more dryness and static electricity. You will wake up feeling better!