What are the exact conditions to use a swamp cooler in? (Phoenix: house, purchase)

[MuscleCar]

Trying to save a little money here, when exactly do you want to use a swamp cooler? Is it something you leave on overnight, or only when the sun comes up and the humidity drops? Is there a max temp they are no longer effective at? Is it a spring and fall only thing? Thank you!

[TimAZ]

With evaporative/swamp coolers, the important number is the dew point, not the temperature. Swamp coolers work best when the dew point (check your local weather forecast online) is less than 40F. As the dew point rises into the 50s, the cooler works less efficiently, and when dew points are in the 60s, forgetaboutit, you're just blowing warm humid air.

[mzbk2l]

Today was perfect! I went up on the roof and cleaned ours up to get it ready for the season. Got done with that around noon and the house was at 79. It took a little while for the pads to get saturated, but by mid-afternoon the house was 74 even as the outside temps were climbing. We had a gathering on the back patio and the cool air coming out of the house was pleasant.

I'll run it 'til mid-late June, maybe using the a/c for an hour or so before bedtime, then probably use a/c most of the time until mid-late September when the evap takes over again.

[Potential_Landlord]

I'm all for doing things myself and make it efficient. Here's why I don't use an evap cooler: in the months where an evap cooler is effective, the AC unit does not use that much more power. My AC uses more power in the monsoon season than the rest of the year by far. That's when you can't use the evap cooler in Phoenix. The cost savings from an evap cooler are thus minimal and only if you do the cleaning yourself. If you hire someone to do it you will save nothing IMO. If you prefer somewhat wetter air in the house then it may be worth it still, but not for the money savings.

[chaparrito]

55 degree dew point is the upper limit.

[mzbk2l]

Originally Posted by Potential_Landlord

I'm all for doing things myself and make it efficient. Here's why I don't use an evap cooler: in the months where an evap cooler is effective, the AC unit does not use that much more power. My AC uses more power in the monsoon season than the rest of the year by far. That's when you can't use the evap cooler in Phoenix. The cost savings from an evap cooler are thus minimal and only if you do the cleaning yourself. If you hire someone to do it you will save nothing IMO. If you prefer somewhat wetter air in the house then it may be worth it still, but not for the money savings.

All good points, and probably enough to keep most people from ever installing one if the house wasn't built with it. If you already have one plumbed into your a/c ductwork, however, it's still cheaper than a/c, and it's hard to beat having the house opened up but still cool on pleasant 90* days for 4-5 months of the year.

We got lucky in that when we finally found a house on property that met all of our other criteria, it had central evap already installed. I would not have invested in one otherwise, but having it available we prefer it over the central a/c during the times it's effective.

[vegas taco]

unless you have an ac purchased in the last few years it will use much more power then a swamp cooler no matter what time of year we have a bonaire durango live in vegas and LOVE IT best purchase we have made

[Obadno]

Never owned one.

[pbenjamin]

The question seemed to be when do you use it if you have it, not whether or not you should have it.

When we had a swamp cooler we would turn it on in the spring when it started getting hot enough for us to want cooling. There was a thermostat of sorts (not temperatures but low...high sort of thing.) We would use it like that, adjusting the "thermostat" as needed until it stopped being efficient, i.e. the dew point would get up to 55 and it would get hot and muggy in the house. That usually happened around the 4th of July. Sometime in September things would dry out and we would start using it again. There would be times in between when it worked OK for a day or two.

It did save money, particularly in June when it would get hot but you could still use it. With the swamp cooler on you could keep doors and windows open a bit and it seemed a lot more pleasant than when you would have to seal things off for the AC.