not sure what your thinking about when you say "open" . most radiant systems are imbedded in some type of substrate (concrete, tile etc) or below an existing floor surface. In the later case efficiencies are reduced.
Solar and other heating systems often use "radiators" of some type which in a way is an "open" type system.
I was curious about this so I did a quick Google search and learned that an open radiant system is where radiant floor heat is mixed with domestic hot water. This source advises against it and says it is best to keep the domestic water system separate.. I'm curious though to hear what experts here have to say about this. KMS?
Yes, this is the conclusion I am coming to as well. However, the house we moved into has an open radiant heating system, so now I'm trying to figure out the best solution. I have been told adding a heat exchanger to our water heater should do the trick, but it is an expensive fix. Not sure which direction to go in now.
Radiant systems can operate at a much lower temp than a domestic hot water system.
As an example solar hydronic system can still "space" heat any time the fluid temp is above the ambient temp. 80 or 90 degrees is still plenty efficient.
To "fix" your system we need to know some more details...is it currently a gas domestic water heater? or are you using some type of boiler? that then feeds a DHW heater.?
You can simply install a combi boiler. This is one that heats both your domestic hot water (faucets) and can provide the necessary heat for radiant heat. These heaters can be expensive to install, but with rebates, local and state programs to help defray the costs, plus the savings you get from using these high efficiency units. They pay for themselves in a few years.
While many people use hot water heaters for providing the heat for radiant systems, they are not designed for that and fail in short order do to build up of hard water byproducts inside the tank.