Why it matters
The Aprilaire Model 400 Whole House Bypass Humidifiers (400M) is a bypass humidifier that mounts on the furnace or its ductwork, rated for homes up to 4000 sq ft.
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 middle 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 Model 620 Whole House Bypass Evaporative Humidifier: rated room size 4000 sq ft here vs 5000 sq ft.
Warranty, per the maker: 5-Year Limited Warranty.
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 sq ft
- 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 Model 400 Whole House Bypass Humidifiers (400M) listing: output per day, power draw. Ask the seller or check the manual before relying on it.
Specifications
The bracket shows where each figure comes from.
| Price | $301.99 | Retailer |
|---|---|---|
| Model number | 400M | Retailer |
| Room coverage | 4000 sq ft | Retailer |
| Output gpd | 17.0 gal/day | Retailer |
| Voltage | 110-120 V | Retailer |
| Fill type | Direct Water Line | Retailer |
| Warranty | 5-Year Limited Warranty | Retailer |
Alternatives worth comparing
More whole-house humidifiers we cover
- Honeywell HE250A1005/U TrueEASE Advanced Large Evaporative Bypass Humidifier 17 GPD $357.99
- Honeywell HE300A1005/U TrueEASE Advanced Evaporative Fan-Powered Humidifier 18 GPD $439.99
- Honeywell HE105A1000/U Whole House Small Bypass Humidifier 12 GPD $199.99
- Honeywell HE100A1000/U TrueEASE Bypass Humidifier 12 GPD $227.99
- Honeywell HE200A1000/U TrueEASE Large Evaporative Bypass Humidifier 17 GPD $254.99
All whole-house humidifiers, compared in one table · Every Aprilaire product we cover
Final verdict
A well-matched choice for homes with forced-air heating. Confirm the model it fits before ordering.
Where to buy
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