Why it matters
The Aprilaire 400 Whole-House Humidifier is a bypass humidifier that mounts on the furnace or its ductwork, rated for homes up to 4000 square feet, with a stated output of 17 gallons per day.
A bypass humidifier uses the furnace blower to push warm air through a wet panel and back into the return duct, so it adds moisture only while the furnace fan runs.
Whole-house humidifiers need a water supply line, a drain for bypass and fan-powered models, and a humidistat; the replacement water panel or canister is a yearly cost.
Price-wise it sat in the dearest third of the 15 bypass models we cover when we checked; the button shows today's price.
It qualifies for our list Best Whole-House Humidifiers, where it is ranked against every model that meets the same rule.
Compared with the Aprilaire 500 Whole-House Humidifier: rated room size 4000 square feet here vs 3000 square feet.
Who it's for, and who should skip it
Good fit if
- Homes with forced-air heating
- Dry winters across the whole house
Look elsewhere if
- Homes without ductwork
Pros and cons
Pros
- Rated for 4000 square feet
- Output 17 gallons per day
- Humidifies every room the ducts reach
Cons
- Professional install for most homes
- Yearly water panel or canister
Limitations to weigh
- Not stated on the Aprilaire 400 Whole-House Humidifier listing: power draw. Ask the seller or check the manual before relying on it.
Specifications
The bracket shows where each figure comes from.
| Model number | 400 | Retailer |
|---|---|---|
| Room coverage | 4000 square feet | Retailer |
| Capacity | 17 gallons per day | Retailer |
Alternatives worth comparing
More whole-house humidifiers we cover
- Aprilaire 720 Fan Powered Evaporative Humidifier (720M) $479.99
- Honeywell HM750A1000/U Advanced Electrode Steam Humidifier $1,019.99
- Honeywell HE240D Whole House Bypass Flow-Through Humidifier (HE240D2001/U) $219.99
- Aprilaire Model 500 Small Bypass Whole House Humidifiers (500M) $229.99
- Aprilaire 500 Whole-House Humidifier
All whole-house humidifiers, compared in one table · Every Aprilaire product we cover
Final verdict
A sensible choice for homes with forced-air heating. Confirm the model it fits before ordering.
Where to buy
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