800 Whole-House Steam Humidifier

Aprilaire 800 would recommend

Aprilaire 800 is awesome.

Aprilair 800 is the best on the market

It really depends on your house and how well sealed it is. We installed a aprilaire 720m and so far has kept our house at 40-45% consistently. But we have a new build, well sealed home. If you have an older leaky house, it may not perform as well. There’s the 800 steam version, but that will use a considerable amount of electricity.

As a general rule, humidity spreads very easily in non-vacuum environments, especially in houses with HVAC systems, open floor plans, and normal air movement. In real homes, moisture doesn’t move by slow diffusion; it moves with air mixing (advection), which is why adjacent rooms often see a rise in RH when a portable humidifier is running in one space. That’s also why a portable unit can run nearly 24/7 without instantly over-humidifying a single room—the added moisture is constantly being diluted into the rest of the house. By contrast, a properly sized whole-house steam humidifier is controlled by a humidistat (either dedicated or built into the thermostat) and cannot run continuously. If a steam unit were allowed to run 24/7, it could easily drive indoor RH toward saturation, whereas recommended indoor RH generally tops out around 50–55% to avoid condensation and mold risk.

**Best option is a whole-house, steam humidifier**, (cold water) plumbed into the supply side of the of the pumping. stream of any salt - based softer, if applicable), with the main thermostat acting as the RH sensor and sending calls to the steam unit. Make sure thermostat window protection is enabled. Examples: **Aprilaire 800** or **Honeywell 750**. The Honeywell can run on **120V or 240V** depending on house size. Max output running 24/7 is roughly: * **5.5 GPD on 120V** * **11 GPD on 240V** Assuming decent insulation and ~9 ft ceilings: * **120V supports ~3,500 sq ft** * **240V supports ~7,000 sq ft** Whole-house steam is the only true *set-and-forget* solution. When outdoor temperatures drop, the system automatically limits indoor humidity—even if the humidity on thermostat is set higher—to prevent window condensation. This protects against water dripping into drywall and potential mold growth. Steam humidifiers are also safer and cleaner. The water is boiled (sterilized), minerals are left behind so you’re not breathing them (vaporized minerals aren’t great for lungs), and there’s no standing water for bacteria to grow. Passive HVAC humidifiers and room units are **not sterilized**. Room humidifiers are manual, hard to dial in l, adjstment, require frequent refilling (usually with distilled water), regular trips to buy heavy jugs, and frequent cleaning to avoid bacteria and mold. By comparison, a whole-house steam unit typically just needs a **cartridge replacement once a year**.

Steam is mainly about control and consistency. It actively generates vapor, so output isn’t tied to furnace runtime and it maintains target RH far more reliably in cold weather. Drip/bypass units like the Aprilaire 700 are cheaper to buy and run, but their effectiveness drops in cold conditions, they only work when the furnace is on, and evaporation leaves minerals behind—causing scale, frequent pad changes, and fine mineral dust entering the airstream, with the issue becoming worse as water hardness increases. Over long periods, inhaling fine particulates is associated with chronic airway irritation, can worsen asthma or other respiratory conditions, and may contribute to long-term lung function decline. Steam still needs maintenance, but it keeps minerals contained in the canister. Cost-wise, bypass units are roughly $20–$40 per season, while steam is closer to $100–$200. In many cold, dry climates, bypass units struggle to get past ~30% RH, while steam remains reliable.

Distilled water is strongly recommended for non-steam portable humidifiers, especially ultrasonic units, because minerals in tap water can be aerosolized and inhaled, and they also cause heavy mineral buildup. With evaporative (wick-based) units it’s less critical for air quality, but still helps reduce scale and frequent part replacement. For steam-based units, low-mineral water does reduce scale, but many electric steam humidifiers (especially electrode-type designs) actually require some mineral content for proper conductivity—using RO or fully distilled water can reduce efficiency, cause faults, or shorten unit life. Room-based steam units without disposable canisters also still have mold risk from standing water regardless of water type, and distilled water doesn’t eliminate the hassle of hauling jugs. That’s why whole-house steam systems are designed to contain minerals in a canister and keep them out of the air instead of relying on distilled water.

We added a humidifier, we went with an April Aire bypass 600 model. The steam humidifiers need an expensive canister replaced yearly. It made a huge difference, for years we used portable humidifiers, the whole house addition was a nice upgrade. Get the automatic humidistat that measures outdoor temp and automatically adjusts.

We install the Aprilaire 600M and 800, so I think you're on the right track. FWIW, we haven't had noise complaints with the 800. The location matters, and it also depends on how noisy the heat pump is when it's running. Is the medical condition just cause sensitivity too humidity? Or is there a bigger indoor air quality component that'll require better ventilation and filtration? And depending on the age of the house, air leakage, and location (climate), I'd be concerned about going above 50% relative humidity in winter. It may or may not be an issue where you live.