Reverse Acting Aquastats

Ginger

I am currently in school for HVAC-R and at the moment I am in class for hot water boilers. We started talking about controls a couple days ago and different options for the system. One option was the reverse acting aquastat to "pre-heat" the water in your boiler. Now at first it didn't seem like a bad idea but when a friend and myself started to discuss it, it no longer seemed so great.
If you were to heat the water to approximately 110 degrees before the pump came on, when the water that was just hanging out in the piping, (that is still at about 70 degrees?) hits the hot boiler sections...isn't that just going to cause thermal shock over and over?
Or...from what my teacher said..is the temperature difference not great enough to cause a problem?

-Ginger

Dale

Domestic water

In some areas it's pretty common to heat the domestic hot water off the boiler, so a low limit or reverse acting aquastat is used to keep the water in the boiler hot enough to heat the house water, no problem with this either. Some techs like a low limit on all systems with oil to help prevent condensation. The cooler return water mixes on startup so no thermal shock. By the way, there are Alot of control systems used in hot water, one of the things any tech needs to do is to figure out first how what they are looking at is supposed to or was designed to work. not always easy. I always take a wire off a high limit to see if the burner shuts off, often it doesn't. Lots of things aren't wired correctly.

Ginger

well..

in most homes in my area they have a hot water heater seperate from the boiler. But, I do see that having a reverse acting aquastat would be a good idea in the case that they were heating their domestic water off of the boiler. I do understand what you are saying- but is there any case where the reverse acting aquastat could cause a problem (aside from if it is wired incorrectly)

Thanks for the feedback by the way