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DIY_user 01-11-2011 08:58 AM

Where should I connect the thermostat ?
I saw an hydronic heating system in a trade show last winter. The system has a tankless hot water box, a heating box, a pump control box with an a couple of external pumps and a hydronic heating unit. I am planning to install hydronic heating in my house. I want to understand how these components work together. Here is what I learned from reading the trade show materials. Please correct me if any of my understanding is wrong.

1. The tankless hot water box provides hot water to heat up the house. It turns on automatically when there is a demand for hot water. It heats up city water.
2. The heating box distributes heated water from the tankless hot water box. It has a build in pump. It is controlled by thermostat. When the thermostat calls for heat, it will turn on the pump which creates the demand for hot water. This demand will turn on the tankless water heater.
3. The pump control is a supplement to the pump of the heating box. it will turn on the external pumps if the hot water distribution circuit is larger than what the internal pump of the heating box can handle. It is controlled by thermostat.
4. The hydronic heating unit provides heat to heat up the space. It is controlled by thermostat. The thermostat can be on the wall or in the floor (if it is a floor heating system) or both. It will call for hot water when the thermostat calls for heat.

If my understanding is correct so far, then my main question is where should my thermostat be connected to? I now have 3 boxes (the heating box, the pump control and the hydronic heating unit) that can be controlled by the thermostats.
My first answer is to connect my wall thermostat to the hydronic heating unit. This will cause the unit to call for hot water when the room temperature is below my settings. But the water will not come unless I turn on the heating box and the external pump. How do these components normally work together?

Jackofall1 01-11-2011 09:04 AM

Sounds like you are talking about (2) systems, one which heats potable water (water from the faucet) and the other heats water for use heating the home.

Thermostat would be connected to the home heating system, as far as the control of the home heating system, ie pumps, boiler, this is accomplished with a control board which is part of the boiler package.

There is a recent post I believe call "Finally Finished My Heating system" with some good pics as to all that is involved.

DIY_user 01-11-2011 12:36 PM

The tankless hot water heater is just providing hot water. The hot water can go to the faucet or the floor heating unit or both. The trade show manuals do not provide the technical details. It just says that there is a priority valve that can switch the hot water flow to the faucet first before flowing to the heating unit if necessary. The set up in the trade show was for hydronic floor heating so the tankless hot water heater is just providing hot water to the floor heating unit. I already have a hot water tank in the house. I am just studying what are my options and how to do it. So I'll try to understand the set up in the trade show which I believe must be working first before I look into other options such as using my existing hot water tank to provide the hot water.

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