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Adding a fan coil to a hydronic system
I have a small staple-up hydronic radiant installation I'm very happy with. There is an electric boiler (Argo) with a loop and circulator pump. There is a circulator pump driving the floor loops. There is a variable speed injection pump between the two.
I also have a hydronic fan coil in my heat recovery ventilation (HRV) duct. This is currently plumbed into my domestic hot water system. I have extra boiler capacity in the Argo and would like to get the fan coil out of my DHW system and into my home heating system. I have two ideas on this.
The first is to put another set of Ts in my boiler loop
and use another pump to circulate water through the fan coil and return it to the boiler loop. This costs me a pump, a relay to control it, and space on my wall to mount it all. It also seems a shame to insert a couple hundred dollars in pumping and control to move the water through twelve extra feet of pipe.
The second is to enlarge the boiler loop (by those twelve feet) to include the fan-coil, placing the it after the injector which feeds the radiant floor. This takes up less space on my wall, only costs me a few valves (to enable bypass of the fan coil), but gives me less control over the heat output.
Control over the heat output isn't a major concern to me. My house can consume any heat the fan coil can provide, and my Argo is currently operating at about 50% capacity. My concern is introducing complication into my short, simple boiler loop.
What do y'all think about either of these approaches? Are both of them bad ideas? Is one worse than the other?