BOSCH WATER HEATER

[snupytcb]

i have a customer who has an existing tankless waterheater used for domestic but wants to add a small piece of radiant. i would like to use this heater because it is already in place and would rather not add another utillity if possible. my plan was to run into an inirect and use the storage for the radiant. my concern is the heater short cycling because of the high return water temps. i have heard of recurc lines doing this and that is cooler water than i would have. i will sell him another boiler if needed but would rather not. will it short cycle?

[Kevin O'Neill]

How much heating load will it have at design conditions? What water flow in GPM through the radieant loop?

[snupytcb]

i have not done to much design yet as i am concerned mostly about short cycling. but i guess the flow will matter. back to the drawing board.

[snupytcb]

now that i think about it the radiant flow will not matter because it is using the storage for water. i can make the coil side flow at whatever i need for the heater to work.

[hotwaterworld]

you could do what you are talking about, flow the outlet water of demand htr through indirect coil, use a recirc pump for house potable to keep how water at the taps and back to demand heater. This will keep the tank hot. Then I might use a Taco mix block pump assy for the radiant floor off tank to modulate water temp to floor based upon outdoor temperature. I might even reverse the hook up to tank and make the potable water go through tank side and the radiant through the coil in tank. This would provide more buffer capacity. The larger volume of water in tank will help reduce the on demand cycling. Maybe run constant circ on the pump with heat demand by floor sensor or room stat. Is this a high temp or low temp floor system. I might be more concerned if it's high temp with this design.