Point of Use Radiant Control from DHW?

KW_2

Our first project with radiant is moving along. Insulators are busy doing their thing - we were able to get the temps up adequately with dry heat. Thanks to everyone who commented on that.


All this thinking about radiant (which is fun!) has me exploring new places for radiant...and I was wondering about something. I would like to add some inexpensive in-wall radiant in a couple of bathrooms, in the showers and behind the towel bars in the area in front of the showers. These 'panels' would be 16" wide by about 48" tall - maybe two of those in the shower and one behind the towel bars. Putting in a separate zone for these seems silly. Just pulling a loop from the floor wouldn't guarantee that the wall panels would be on for the few minutes needed. System is being driven by a Munchkin boiler which also loads a 60 ga DHW tank. So what about simply pulling a line from the DHW system? Is there a valve that could be controlled by a simple wall 10 minute timer (like a bath vent timer)? This could easily be flipped on just when needed. This would prevent short cycling the boiler too. I thought about simply running the HW feed to the shower head through the panel but I'm concerned that controlling the water temp in the shower would be hard and in the summer you might not want the wall panels on. Is this a problem, or do you simply adjust the shower valve a bit hotter - resulting in water from the shower head at the proper temp?


BUT, does this now enter the world of "open" DHW/radiant systems that I know is not a good idea? I suppose that water in those loops may sit all summer, and then when first used in the fall that stagnant, nasty, possibly bug-filled water will be mixed into the DHW system, right?


So what is the correct and most cost-effective way to add this type of small, creative radiant panels into a system?