Coordinate hot water heat with steam heat

DanielC

I have steam heat in most of the house and hot water baseboard heat in an upstairs addition. The steam heat has a programmable thermostat. The hot water heat is piped off a tankless water heating fitting from a new Weil-McLean EG45 steam boiler. The hot water loop has a non-programmable Honeywell T87F thermostat wired to the circulator pump.

What I want is the steam system to heat the house when it needs to be heated, and the hot water to heat the addition when that needs to be heated. I don't want the hot water heat to turn on the steam heat if it's not necessary.

Recently I replaced the boiler (it had cracked), the near boiler steam piping, and hot water piping in the boiler room. Whereas previously the hot water would flow upstairs by convection without the circulator pump running, now I only get heat upstairs when I turn up the upstairs thermostat manually. Unfortunately, that ignites the burner and pumps extra heat into the steam piping even when I don't want them to heat up at all or if they've already gotten sufficiently warm enough. Sometimes the pressure in the steam boiler rises, forcing the pressuretrol to cut off the burner. That may be due to the upstairs thermostat calling for heat but I'm not certain.

I could put a programmable thermostat upstairs and coordinate the schedule with the downstairs programmable thermostat. I don’t know if that's the optimal approach.

What are my options?

Thanks!

nicholas bonham-carter

The hot water loop temperature should be controlled by an aqua stat which should keep the water loop well below boiling point. There are some excellent articles on this site about the installation of a hot water loop on a steam boiler, including the control strategy of a second thermostat.
Generally speaking, most installations would circulate the water in the boiler, instead of using the hot water coil, which may need hotter water to operate.—NBC

KC_Jones

If the hot water system is causing you to make steam you have a control issue at the boiler. It shouldn’t make steam even if the hot water system called for heat for hours.

Post some pictures of your set up.

DanielC

Here are four pictures of my configuration. They are the front, right, and left sides of the boiler. The fourth picture is the piping for the hot water loop. The dark shape on the upper right hand corner of the last photo is the circulator pump.

KC_Jones

I don’t see an aquastat anywhere, am I missing it?

Without an aquastat there is nothing to shut the burner down when the hot water is calling for heat. That most likely is your problem.

DanielC

Here's a photo of the configuration behind the front cover. The item on the left around which I drew a red box has wires coming out that are not connected to anything. When the contractor did the original install, the burner ran even when the thermostat was not calling for heat. He said the problem was that the system was set up for DHW, and so it was providing heat to keep the DHW hot. So apparently he disconnected that.

KC_Jones

Ask him his plan to limit burner firing to not make steam when the hot water is calling.

There needs to be a limit, you don’t want to make steam when the hot water calls. If the steam is calling it doesn’t matter, as long as he has a mixing valve on the hot water to limit those temps, it appears you do have that.

I’m not saying that disconnected control is the proper control, I’m saying he needs something there to detect water temps and shut the burner down before it steams. I can see what appears to be the thermostat wires in that picture and it looks like they are wired parallel. Basically both thermostats are functioning as steam thermostats and you are at the mercy of the steam controls.

DanielC

Thank you for your help. I will follow up with him after the weekend.

DanielC

My contractor has installed an aquastat to prevent the burner from making steam when the hot water thermostat is calling for heat. When: the hot water thermostat is calling for heat and the aquastat detects that the water is too hot, then: the aquastat will stop the call to fire the burner and the circulator pump will continue to run. The house is more comfortable now.

Thanks for your comments.