This question only makes sense in the context of solar hot water heating. But it is also a plumbing question. One solar manufacturer sells a heat dissipator unit whose purpose is in the summer to get rid of excess heat produced by an evacuated tube solar hot water panel used with closed loop glycol. This heat dissipator can be plumbed as a side track of sorts. You can use a 3-way solenoid operated valve to divert the water to the dissipator. The controller can take care of that. That's probably the standard way. But now we come to my question. The literature on this dissipator says, "Alternatively a thermostatic mixing valve/tempering valve set to a suitable temperature can be used, providing mechanic, automatic regulation of flow through the heat dissipator." So how would that be plumbed? When the TMV is used in a typical DHW application, you would have hot (H) in and cold (C) in and warm (W) out. If I see it right, for my solar dissipator, I would need to plumb the TMV in reverse... so that the main incoming line would connect to W, the normal outgoing line would connect to H and the diversion line going to the dissipator would connect to C. So the water would be flowing in the opposite direction through the valve from the usual. Is that correct? If not what is correct? And why?