If the shower head I bought for my recent remodel is of the type you're referring to (it's a Kohler Pinstripe Pure shower head of the "Katalyst" variety, which allegedly aerates to create a more realistic, heavy drop), I don't notice any odd temperature fluctuations at all. Plus, couldn't you just adjust the thermostatic valve hotter... My shower is the same temperature every day regardless of whether other toilets are flushed, dish/clothes washers going, etc.

I don't think these shower heads are designed to save water. At least that's not what Kohler is advertising them as.

http://www.youtube.com/watch?v=Eirm_-3OtMg

Thank you for your reply. What I meant was that Hansgrohe advertises that they add 3 parts of air to 1 part of water. The rationale is that the shower head will provide a fuller feeling shower by using injected air while still saving water. My concern is that adding ambient air to the shower stream will cool the water. Turning up the thermosatic value will use up my hot water faster and increase my electric bill. So while the air injected shower head may save water and reduce my water bill it may raise my electric bill if I have to use more hot water.

That is why I was hoping for some feedback on how much injecting air into the shower spray cools it off. As I mentioned Consumer Reports says it can be as much as 15 degress which is significent.

I have a Hansgrohe Raindance 240 head. It might cool the water down. I just set the water hotter to make up for it, if in fact the water is getting cooled.

We had the Hansgrohe in our last home(air injection and loved it) put same one in new home and water is definitely cooler plus pressure is a lot lower. Is there something plumber has to do before installing an air injection? I'm wondering if installed proper.

james-

I'd be interested in seeing a link to the Consumer Reports test results. I usually think they do a good job of testing, but as an engineer I'm skeptical that you would get that amount of cooling from air injection in a shower head.

You mention a ratio of 3 parts of air to one part of water, which I assume is on a volume basis (as opposed to a weight basis). From a thermodynamics standpoint, the amount of cooling claimed doesn't make sense to me because the heat capacity of water is several thousand times that of the same volume of air.

I won't bore you with the calculations, but I'll just say that, if you mixed three parts of air at 70 degrees F (typical room temperature) with one part of water at 105 degrees F (typical shower temperature), the air would cool the water by a trivial amount...a small fraction of a degree. It would be like adding a couple of drops of cold water to a gallon of hot water...you wouldn't be able to sense the difference.

Maybe there is something else going on here mechanically that I'm not aware of, but, from a pure thermodynamics standpoint, the mixing of hot water with some slightly cooler air is just not going to result in a noticeable decrease in temperature. And, after a minute or two of showering, the mist-laden air will have picked up enough heat from the shower spray that the room air temperature will be even closer to the temperature of the hot water coming from the shower head.