Whole house humidifier cost

A whole-house humidifier costs $400 to $1,300 installed, typically around $700. It mounts on the ductwork beside the furnace and adds moisture to the whole house rather than one room, which matters in a cold climate where winter heating drives indoor humidity down to the low twenties.

There are three types and they differ more in running cost and maintenance than in purchase price.

What it costs

Running cost is small for bypass and fan-powered units, since they use the furnace's own heat. A steam humidifier boils water electrically and can add $10 to $30 a month to the bill in a cold winter.

The three types

Bypass humidifiers divert a little warm supply air across a wet pad and return it to the return duct. Cheapest, no fan, no electricity beyond the solenoid. They need a bypass duct, which needs room beside the furnace, and they only work when the furnace is actually running.

Fan-powered units have their own small blower, so they do not need the bypass duct and produce more moisture per hour. Slightly more expensive, slightly more capable, and the usual recommendation for most houses.

Steam humidifiers boil water and inject steam. They work regardless of whether the furnace is heating, which makes them the right answer for a heat pump or a very large or very dry house. They cost several times as much to buy and to run, and they need a dedicated circuit.

Whether you need one

The honest test is a $12 hygrometer. Put it in the main living space for a week in the coldest part of winter and read it.

• Below 30% is dry enough to be worth acting on
• 30 to 50% is the target range
• Above 50% in winter is too much, and the problem is condensation, not dryness

The symptoms people attribute to dry air are real: static shocks, cracked wooden furniture and floors, split instruments, dry sinus passages, and a house that feels colder than the thermostat says because dry air pulls moisture off your skin.

But those same symptoms come from a leaky house, and a humidifier fighting an air leakage problem runs constantly and never wins. If you have single-glazed windows and a drafty envelope, air sealing is the better first purchase, and it makes the humidifier smaller and cheaper if you still want one.

The failure mode to avoid

Too much humidity in a cold climate is worse than too little. Moisture condenses on the coldest surfaces, which are the windows first and then the inside of exterior walls where you cannot see it.

The rule is to lower the setting as it gets colder outside:

If you get condensation running down the inside of the windows, the setting is too high whatever the table says, and the windows are telling you what is happening inside the walls.

An automatic humidistat with an outdoor sensor does this adjustment for you and is worth the $80 to $200. A manual dial set once in November and forgotten is how people end up with mold around the window frames by February.

Maintenance is the whole story

A humidifier is a device that keeps a pad permanently wet inside warm ductwork. It is maintained or it becomes a problem.

• Replace the water panel or evaporator pad every heating season, or twice in hard water areas
• Check the solenoid valve and the drain line each fall
• Turn the water supply off at the end of the heating season and the humidistat to off, so it does not run in summer
• Descale the distribution tray annually where water is hard

An abandoned humidifier left connected is a slow leak waiting to happen and a reliable source of the smell people blame on their ducts.

Frequently asked questions

Will a humidifier make the house feel warmer?

Slightly, and it is not imaginary. Moist air slows evaporation from your skin, so most people are comfortable a degree or two lower. It is not enough to pay for the unit in heating savings, whatever the brochure implies.

Can I fit one to a heat pump?

Bypass and fan-powered units work poorly with heat pumps, because heat pump supply air is much cooler and carries less moisture. Steam is the type that suits a heat pump, which is why heat pump households pay more for humidification.

Are portable room humidifiers a reasonable alternative?

For one bedroom, yes, and they are much cheaper. For a whole house, no: you would need several, they need filling daily, and they are the ones that grow biofilm if neglected.

Does the water need filtering?

Not usually. Hard water shortens the life of the pad and scales the tray, so budget for more frequent pad changes rather than a filter.

Will it help with a dry throat and nosebleeds in winter?

Bringing a house from 20% to 35% relative humidity genuinely helps most people with that. It is the most common reason people fit one, and the one where the result is most noticeable.