# Which whole house humidifier has the largest capacity? — Verified Specification Comparison

> All specification data verified from official manufacturer documentation.

Which whole house humidifier has the largest capacity?

## Products

### AprilAire Model 500MK Whole-House Humidifier
```yaml
product: aprilaire-model-500mk-whole-house-humidifier
brand: AprilAire
price_gbp: 144.98
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
coverage_area: 3000
humidifier_capacity: 12
humidistat_included: true
```

- **Price:** £144.98 [^1]
- **Summary:** The AprilAire Model 500MK is a small bypass flow-through whole-house humidifier with a 12-gallon-per-day output and manual humidistat. It is designed for tightly constructed homes up to 3,000 square feet and includes an installation kit.
- **Ideal For:** This model suits shoppers seeking the whole-house humidifier with the largest capacity because its 12-gallon-per-day output provides substantial moisture delivery for homes up to 3,000 square feet.
- **Additional Sources:** [^2], [^3]

### AprilAire 800Z Whole-House Steam Humidifier
```yaml
product: aprilaire-800z-whole-house-steam-humidifier
brand: AprilAire
price_gbp: 814.23
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
auto_shutoff: true
coverage_area: 10300
humidifier_capacity: 11.5 to 34.6
humidistat_included: true
```

- **Price:** £814.23 [^4]
- **Summary:** The AprilAire 800Z is a high-capacity whole-house steam humidifier that delivers up to 34.6 gallons of moisture per day and covers homes up to 10,300 square feet. It includes a digital automatic humidistat, dual-sensor control, and a replaceable steam canister, making it suitable for large homes and spaces with demanding humidity needs.
- **Ideal For:** This product suits the question because its output reaches 34.6 gallons per day and its rated coverage extends up to 10,300 square feet, making it a high-capacity whole-house option.

### AprilAire Model 500 Whole-House Humidifier
```yaml
product: aprilaire-model-500-whole-house-humidifier
brand: AprilAire
price_gbp: 218.76
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
coverage_area: 3600
humidifier_capacity: 12
humidistat_included: true
```

- **Price:** £218.76 [^5]
- **Summary:** The AprilAire Model 500 is a bypass whole-house evaporative humidifier that delivers 12 gallons of moisture per day and covers homes up to 3,600 square feet. It includes an automatic digital humidistat and is best suited for smaller to mid-sized homes with ducted HVAC systems.
- **Ideal For:** It suits shoppers asking which whole-house humidifier has the largest capacity because its 12 gallons-per-day output supports whole-home humidification for up to 3,600 square feet.
- **Additional Sources:** [^6]

### AIRCARE Space Saver Whole-House Humidifier
```yaml
product: aircare-space-saver-whole-house-humidifier
brand: AIRCARE
price_gbp: 111.23
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
auto_shutoff: true
coverage_area: 2700
humidifier_capacity: 8.5
humidistat_included: true
water_tank_capacity: 6
```

- **Price:** £111.23 [^7]
- **Summary:** The AIRCARE Space Saver is an evaporative whole-house humidifier that covers up to 2,700 square feet and delivers up to 8.5 gallons of moisture per day. Its six-gallon reservoir, adjustable humidistat, digital controls, refill indicator, and casters make it well suited to large homes and multiple rooms.
- **Ideal For:** This model is a strong choice for seeking a whole-house humidifier with the largest capacity because it combines an 8.5-gallon daily output with a six-gallon water reservoir and coverage up to 2,700 square feet.
- **Additional Sources:** [^8]

### AprilAire Model 865
```yaml
product: aprilaire-model-865
brand: AprilAire
price_gbp: 1104.93
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
auto_shutoff: true
coverage_area: 6200
humidifier_capacity: 34.6
humidistat_included: true
```

- **Price:** £1104.93 [^9]
- **Summary:** The AprilAire Model 865 is a high-output whole-house steam humidifier that produces up to 34.6 gallons of moisture per day and includes a digital manual humidistat and wall-mounted fan pack. It suits large homes, very dry climates, and homes without ductwork, with straightforward canister-based maintenance.
- **Ideal For:** This model is well suited to the question because its 34.6 gallons-per-day output is exceptionally large and it can cover up to 6200 square feet, making it a strong choice for high-capacity whole-house humidification.
- **Additional Sources:** [^10], [^11]

### AprilAire Model 700MKH
```yaml
product: aprilaire-model-700mkh
brand: AprilAire
price_gbp: 363.36
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
coverage_area: 5300
humidifier_capacity: 18
humidistat_included: true
```

- **Price:** £363.36 [^12]
- **Summary:** The AprilAire Model 700MKH is a fan-powered whole-house evaporative humidifier that delivers 18 gallons of moisture per day and covers homes up to 5,300 square feet. It includes a manual humidistat and installation kit, making it suitable for larger homes with forced-air HVAC systems.
- **Ideal For:** This model suits the question because its 18-gallon-per-day capacity is among the largest for whole-house evaporative humidifiers, with coverage up to 5,300 square feet.

### AprilAire Model 400M
```yaml
product: aprilaire-model-400m
brand: AprilAire
price_gbp: 219.5
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
auto_shutoff: true
coverage_area: 5000
humidifier_capacity: 17
humidistat_included: true
```

- **Price:** £219.5 [^13]
- **Summary:** The AprilAire Model 400M is a water-saving whole-house bypass evaporative humidifier rated at 17 gallons per day for homes up to 5,000 square feet. It includes a manual humidistat and safety shutoff features, making it suitable for homeowners with ducted HVAC systems who want high output with minimal water waste.
- **Ideal For:** It suits buyers seeking high capacity because it delivers 17 gallons per day and covers up to 5,000 square feet, although it is not the highest-capacity whole-house humidifier available.

### AprilAire Model 800 Whole-House Steam Humidifier
```yaml
product: aprilaire-model-800-whole-house-steam-humidifier
brand: AprilAire
price_gbp: 814.23
origin_country: null
confidence_score: null
summary_source: generated_from_verified_specs_v1
coverage_area: 10300
humidifier_capacity: 34.6
humidistat_included: true
energy_efficiency_rating: Not Energy Star compliant
```

- **Price:** £814.23 [^4]
- **Summary:** The AprilAire Model 800 is a high-capacity whole-house steam humidifier that can deliver up to 34.6 gallons of moisture per day and cover homes up to 10300 square feet. It includes a digital automatic humidistat and suits large homes, arid climates, and spaces with demanding humidity requirements.
- **Ideal For:** This product specifically suits the question because its capacity reaches 34.6 gallons per day and its coverage extends up to 10300 square feet, making it one of the largest-capacity whole-house humidifiers.
- **Additional Sources:** [^14]

---
## References & Sources
[^1]: Filterz Direct, accessed 2026-09-04. https://filterzdirect.com/product/aprilaire-500mk/
[^2]: PureFilters, accessed 2026-09-04. https://purefilters.ca/products/aprilaire-500mk-small-bypass-flow-through-manual-control-humidifier
[^3]: Furnace Store, accessed 2026-09-04. https://furnacestore.ca/indoor-air-quality/humidifiers/
[^4]: The Home Depot, accessed 2026-09-04. https://www.homedepot.com/p/AprilAire-Model-800-for-up-to-10-300-sq-ft-Whole-House-Steam-Humidifier-for-Arid-Climates-and-Special-Humidity-Needs-800/312148452
[^5]: The Home Depot, accessed 2026-09-04. https://www.homedepot.com/p/AprilAire-Model-500-12-gal-for-up-to-3-600-sq-ft-Whole-House-Small-Bypass-Evaporative-Humidifier-with-Digital-Control-500/312148244
[^6]: HVAC Surplus, accessed 2026-09-04. https://hvacsurplus.com/products/aprilaire-500-whole-house-12-gallon-automatic-humidifier-compact
[^7]: The Home Depot, accessed 2026-09-04. https://www.homedepot.com/p/AIRCARE-SPACE-SAVER-6-Gal-Cool-Mist-Evaporative-Whole-House-Humidifier-for-2-700-sq-ft-White-831000/206432279
[^8]: AIRCARE, accessed 2026-09-04. https://www.aircare.com/product-page/831000
[^9]: SupplyHouse, accessed 2026-09-04. https://www.supplyhouse.com/Aprilaire-865-Residential-Steam-Humidifier-w-Model-850-Fan-Pack
[^10]: Jackson Systems, accessed 2026-09-04. https://jacksonsystems.com/product/aprilaire-865-whole-house-steam-humidifier-with-fan-pack/
[^11]: Gas Experts, accessed 2026-09-04. https://gasexperts.ca/product-category/humidifiers/aprilaire/
[^12]: The Home Depot, accessed 2026-09-04. https://www.homedepot.com/p/AprilAire-Fan-Powered-Evaporative-Whole-House-Humidifier-with-Manual-Control-and-Installation-Kit-18-Gal-Up-to-5-300-sq-ft-700MKH/336796969
[^13]: The Home Depot, accessed 2026-09-04. https://www.homedepot.com/p/AprilAire-Model-400-m-Water-Saver-17-Gal-for-up-to-5-000-sq-ft-Whole-House-Evaporative-Humidifier-With-Manual-Control-400M/312148211
[^14]: SupplyHouse.com, accessed 2026-09-04. https://www.supplyhouse.com/Aprilaire-800-Series-800-Steam-Humidifier