I am moving to Colorado, where having a whole house Evaporative (Swamp) Cooler is both effective and low cost option for cooling my home.

Additionally, Colorado is drier, so a whole house humidifier is attractive as well, especially in the dry winter months.

The home in question has central heating. Duct work is present already in the house and it is capable of simply blowing air (with no heat).

Looking at the the basic function of swamp coolers and whole-house humidifiers, they appear to be very, very similar. Is there a system which can fill both functions for the whole house?

The major differences between these systems (at least for units designed to affect a whole house) appear to be:

  • Evaporative Coolers take outside air and cool it (humidity is a side effect) whereas humidifiers take an inside air and make it wet (decreases in temperature is a side effect).
  • Slight differences in the absorption medium: they appear to be optimized one way or another. I suspect outside of form and fit, they have the same function; to increase surface area so air can take up water.
  • Installation preferences: whole-house swamp coolers tend to be outside (on roofs) and require special attention to avoid broken pipes in the winter. Whole-house humidifiers tend to be inside, some even fitting inside/on duct work. The reason for these seem to be simply accessing required resources or duct work more easily.

A bonus: if no commericial options are available, what is the downside of placing one of these in my home (to avoid freezing) with some duct work to taking outside or inside air as I desire?

  • As a note, I realize evaporative cooling requires dry air for any sort of effect, so humidifiers only temporarily cool recirculated air. Once humidity steady-state is achieved (or as close as a house can get to that), a humidifier won't do much to the temperature. This is where switching air source would come in; humidify during winters, cool+humidify during summers. Two functions, one system- does it exist?
    – PipperChip
    Commented Aug 30, 2021 at 16:42
  • Usually when you try to add two things together, they usually get more expensive, and are worst at doing both jobs.
    – crip659
    Commented Aug 30, 2021 at 17:15
  • @crip659 Yes, usually... But if the main difference is where the initial air came from, people could save an order of magnitude of money by getting a whole house humidifier and getting a intake from outside (and valve). Surely I am not the first to think this!
    – PipperChip
    Commented Aug 30, 2021 at 17:45

2 Answers 2


It's true that a swamp cooler and a humidifier (together with its associated furnace/air handler) both have "blow air around" and "make the air wet" on their lists of features. But the scale at which they do those things is so different that it doesn't make sense to have one piece of equipment do both jobs.

  • Furnace air flow: about 1000 CFM. An article at Contracting Business asserts that, as rules of thumb, average cooling airflow for an air conditioning system is 400 CFM per ton of cooling and heating airflow for a condensing furnace is 150 CFM per 10,000 Btu/hr of input. I'll claim that a hypothetical system within the range of "average" might include an 60,000 Btu/hr furnace and a 2.5 ton air conditioning unit to condition the air in a 3000 square foot house. Based on the rules of thumb, this system might require a blower capacity of 1000 CFM for cooling and 900 CFM for heating. As a cross-check, the specs of an arbitrarily-chosen Goodman GMES960603BN furnace are 60,000 Btu/hr input and 1200 CFM maximum. Duct systems are sized accordingly: many trunks are rectangular in the range of 10x14 to 10x20 inches (140-200 square inch cross section).

  • Swamp cooler air flow: about 4000+ CFM. A page at Energy.gov asserts that "Manufacturers recommend providing enough air-moving capacity for 20 to 40 air changes per hour, depending on climate." Suppose that hypothetical house has 3000 square feet of floor area and is a rambler style (so half the house is basement and doesn't need cooling). With typical 8 foot high ceilings in the above-ground level there are (3000/2) * 8 = 12000 cubic feet. To change that air at the minimum of 20 times per hour, ie once every 3 minutes, we'll need 12000/3 = 4000 CFM of swamp cooler capacity. The duct coming off a swamp cooler of this size is often 20x20 square or even larger (400 square inch cross section).

  • Pad area: 25x more in a swamp cooler. The inexpensive evaporative/bypass type humidifier in a furnace uses a relatively small pad -- only about 1 square foot of area -- and only a small fraction of the furnace's 1000 CFM actually passes through the pad. A 4000 CFM swamp cooler, on the other hand, will likely have four pads 2.5 feet square for a total of 25 square feet. It would be challenging to effectively pack that much surface into a furnace-sized box.

  • Delta-T vs humidity: The point of a humidifier in winter months is to add as much humidity as possible inside the home (to some limit). The point of a swamp cooler in summer months is cooling; humidification is undesirable. In fact, performance is best (delta-T or change in temperature is greatest) when humidity in the supply air is lower. One manufacturer (Portacool) expects 24°F of cooling when conditions are 90°F/20%RH, but just 11°F cooling with conditions of 80°F/60%RH. One would never want to re-circulate evaporative-cooled air because as the RH of the input air rises the cooling effect tapers off quickly. Within a matter of minutes the space would feel like a warm sticky swamp rather than refreshing cool air.

Combining swamp cooler and humidifier all into the forced-air furnace system would require significant increase to duct expense, incur rapid rusting out of the furnace, and substantially complicate architecture of the house due to the very large intake air duct that would be required to extend to the furnace.

As crip659 wrote in a comment: [the system would] get more expensive and [be] worse at doing both jobs.


Are you planning to purchase an existing home or build your home from the ground up? If building from the ground up it might be interesting to look into geothermal climate control.

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    Commented Sep 1, 2021 at 8:58

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