Heating and cooling
Whole-house humidifier installation cost
A bypass humidifier on a gas furnace costs about $680 installed; fan-powered about $860; steam about $2,040 with the 240 V circuit it needs. The size comes first: a 2,000 sq ft house of average tightness in a cold zone loses about 9.2 gallons of water a day through air leakage. On a heat pump only steam keeps up.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-28 · Nothing you type leaves your browser
Whole-house humidifier sizing and cost calculator
The house, the climate and the heating
A humidifier replaces the water that leaves with the air leaking out. The size of the house, how leaky it is and how cold it gets decide how many gallons a day that is.
Most houses: some drafts at doors and windows, a fireplace damper, a few leaks at the attic.
Design day 5°F; hold about 28% inside.
Warm supply air evaporates well: any type works.
The cheapest that keeps up.
Gravity drain.
Manual humidistat.
Used only to pick a regional labour rate. It stays in your browser.
Bypass, 12 gal/day, installed
$680
$430–$1,025 · about $25 a year to run
9.2 gallons a day on the design day
This unit gives about 12 on gas or oil furnace — enough.
Colder is not wetter
Hold 28% at 5°F.
The colder it is outside, the lower the humidity a house can hold before the windows fog and drip. That is why a humidifier in a very cold climate can be smaller than one in a milder one.
Bypass, fan-powered or steam
2,000 sq ft, average, on gas or oil furnace.
What the installation includes
- Bypass, 12 gal/day
A water panel in the warm air, with a duct from the supply to the return. Runs on the furnace's blower: no motor of its own.$220 - Installation
An HVAC technician mounting it on the duct with the bypass run to the return, wiring it to the furnace and the control, and setting it up.$400 - Water feed
A saddle or tee valve on the nearest cold line and the feed tubing.$40 - Drain line
Tubing to the floor drain.$20
What it costs
National average. A bypass, 12 gal/day humidifier fitted to an existing gas or oil furnace, with its water feed and drain. A year to run: a new water panel every heating season..
The furnace it runs on: furnace installation; on a heat pump: heat pump installation.
Worth knowing
- On a 5°F design day in zone 5, 2,000 sq ft at 0.75 air changes an hour needs about 9.2 gallons of water a day to hold 28% inside. The setting drops as it gets colder — at 0°F it is 25% — or the windows run with condensation.
- A bypass unit sends part of its water to the drain to keep the panel clean — it needs a drain within reach or a condensate pump — and a new water panel each fall.
On this page — 4 sections
Installed, by type
The short version
- Bypass on a furnace: $680. The usual choice.
- Fan-powered: $860. No bypass duct, more output.
- Steam: $2,040. With its 240 V circuit; the one for heat pumps.
- Size first: 9.2 gallons a day for 2,000 sq ft, average house, cold zone.
A bypass humidifier hangs on the furnace ductwork, with a small duct to the return that pushes warm air through a wet panel. A fan-powered unit adds its own fan and loses the duct. A steam unit boils water with an electric element and injects it — it costs more to buy, to install and to run, but it is the only one that keeps up on a heat pump or a big, leaky house.
| Installed | A year | |
|---|---|---|
| Bypass | $680 | $25 |
| Fan-powered | $860 | $25 |
| Steam | $2,040 | $668 |
$680
Bypass
Installed
$2,040
Steam
With 240 V circuit
9.2 gal
A day
2,000 sq ft, zone 5
28%
Target
At 5°F outside
MaterialsEstimator, Whole-house humidifier price survey · checked 2026-09-28
Sizing: the water that leaks out
Winter air is dry because cold air holds almost no water, and every cubic foot that leaks in has to be brought up to indoor humidity. A humidifier is sized by that: the house’s volume, how many times an hour the air is replaced, and the gap between the water in indoor and outdoor air.
gallons a day = volume × air changes an hour × 0.075 lb/ft³ × (indoor − outdoor humidity ratio) × 24 ÷ 8.34
| Air changes an hour | 2,000 sq ft, zone 5 | |
|---|---|---|
| Tight — newer, sealed | 0.35 | 4.3 gal/day |
| Average | 0.75 | 9.2 gal/day |
| Loose — older, drafty | 1.25 | 15.3 gal/day |
ASHRAE, ASHRAE Handbook — Fundamentals, Psychrometrics and Ventilation and Infiltration · checked 2026-09-28
Colder outside, lower inside
| Indoor setting | 2,000 sq ft, average | |
|---|---|---|
| 30°F outside | 40% | 9.8 gal/day |
| 20°F outside | 35% | 10.1 gal/day |
| 10°F outside | 30% | 9.6 gal/day |
| 0°F outside | 25% | 8.6 gal/day |
| -10°F outside | 20% | 7.2 gal/day |
| -20°F outside | 15% | 5.5 gal/day |
The inside of a window is as cold as the weather lets it be, and humid air condenses on it. So the humidity a house can hold falls as the temperature does — which is why a humidifier in a very cold climate can be smaller than one in a milder climate, and why an automatic control that reads the outdoor temperature is worth its $120.
Whole-house humidifier manufacturers, Humidifier sizing guides, capacities and recommended settings · checked 2026-09-28
What goes wrong
Before the installer comes
- The heating type — furnace, heat pump or boiler.
- A floor drain near the furnace, or not.
- A cold water line within reach.
- Space on the supply or return duct.
- A spare breaker space, for steam.
01A bypass unit on a heat pump
Lukewarm air evaporates about half as much.
Instead — Steam.
02One setting all winter
Cold snaps put water on the windows.
Instead — An outdoor-sensing control.
03Never changing the panel
Minerals block it and output drops.
Instead — A new panel each fall.
04Humidifying a leaky house
The water leaves as fast as it is added.
Instead — Air-seal first; the humidifier gets smaller.
- 01Work out the volumeHeated square feet times the ceiling height.
- 02Judge how leaky the house isTight, average or loose — it sets the air changes per hour.
- 03Take the design dayThe zone's cold winter temperature, and the lower humidity the house can hold then.
- 04Turn it into gallons a dayThe air coming in times the moisture it lacks.
- 05Pick a type that keeps upBypass or fan-powered on a furnace; steam on a heat pump or a big load.
- 06Add the drain, water and powerA pump without a floor drain, a 240 V circuit for steam.
Sizing and pricing the furnace the humidifier runs with.
The furnace it hangs on- Bypass humidifier
- A water panel mounted on the furnace ductwork, with a small duct from the supply to the return that pushes warm air through it. It uses the furnace blower.
- Fan-powered humidifier
- The same water panel with its own fan, so it needs no bypass duct and puts out more.
- Steam humidifier
- Boils water with an electric element and injects the steam into the duct. It works whatever the supply air temperature.
- Gallons per day (GPD)
- A humidifier's rated output, and the unit its sizing is done in.
- Air changes per hour (ACH)
- How many times the house's air is replaced by outside air in an hour through leaks. The main number in humidifier sizing.
- Humidity ratio
- Pounds of water vapour per pound of dry air. Cold air holds very little, which is why heated winter air is dry.
- Design temperature
- The cold winter temperature a heating or humidifying system is sized for in a climate zone.
- Water panel
- The pad in a bypass or fan-powered unit that water runs over and air passes through. Replaced every season.
Common questions
- How much does it cost to install a whole-house humidifier?
- About $680 for a bypass humidifier on a gas furnace — $220 for the unit and $400 to install it, with the water feed and drain. A fan-powered unit is about $860 and a steam unit $2,040, including the 240 V circuit it needs.
- How much does a furnace humidifier cost?
- A bypass unit is about $220 and a fan-powered one $350 before installation; fitted, $680 and $860. Without a floor drain nearby, add a condensate pump — and a digital control with an outdoor sensor, $120, takes it to $890.
- What size whole-house humidifier do I need?
- A 2,000 sq ft house with 8 ft ceilings needs about 4.3 gallons a day if it is tight, 9.2 if average and 15.3 if loose, on a 5°F design day. It is the air leaking in that decides it: the humidifier replaces the water that leaves with it.
- What is the best humidifier for a heat pump?
- Steam. A heat pump's supply air is only lukewarm, so a bypass unit gives about half its rating — 8.5 of 17 gallons a day here. A steam unit is $2,040 installed and puts out its full rating on any system.
- How much does a steam humidifier cost to run?
- About $588 a year of electricity for a 2,000 sq ft house through a six-month heating season at $0.17 a kWh, plus about $80 for a new cylinder or a cleaning. A bypass unit costs about $25 a year for its water panel and nothing to run beyond the water.
- What humidity should I set in winter?
- Lower as it gets colder: about 40% at 30°F outside, 30% at 10°F, 25% at 0°F and 15% at −20°F. Above that, water condenses on windows and in walls. An automatic control with an outdoor sensor does the lowering for you.
- Can I install a whole-house humidifier on a boiler?
- Not the usual kind: it works through the ducts, and a boiler with radiators has none. Room humidifiers, or a ducted steam unit with its own small air handler, are the alternatives.
- How much does a humidifier cost for a large house?
- A 3,500 sq ft loose house in a cold climate needs about 23 gallons a day — past any bypass or fan-powered unit — so a 35-gallon-a-day steam unit, about $2,640 installed.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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