Piping an indirect or baseboard to a steam boiler

Caution: All drawings are conceptual drawings for illustration purposes only and may be incomplete. More specific drawings may be needed for your application.

Piping an indirect water heater into a steam boiler is not an uncommon application with gas or oil-fired steam boilers. There are a few key points we need to discuss before proceeding with the piping.

For information, adding a Hot water baseboard at the same level or above the steam boiler click here

Below are some guidelines to follow when installing h/w baseboard or an indirect water heater at the same level as the boiler.

We can return the water from the indirect to a boiler tapping normally in the opposite end of the boiler from the supply. This will avoid short cycling of the water within the boiler. If you pipe into the steam system return pipe, the pipe must be on the boiler side of the Hartford loop.
The boiler should have at least one 1" or larger tapping higher in the boiler than the return tapping.
Use an aquastat to keep the boiler from creating steam on demand for DHW or HW baseboard only. A separate control tap in the boiler, slightly higher than the IWH pipe tapping, works best.
The control taping can be as small as 1/2" for the control well. A piping strap-on control works, but it is slightly more difficult to stop the boiler from steaming. A control in the boiler is much more accurate.
It is best to use a bronze or stainless circulator to pump this water. Although many have used smaller wet-rotor circulators, it is best to use a three-piece circulator. The circulator must pump away from the boiler. Think of the boiler as the expansion tank connection
The piping from the supply tapping must elbow down toward the floor and mount the circulator close to the floor to keep the live steam away from the inlet of the circulator in case of surging water. If steam enters the circulator, it can cause the circulator to fail.
It is a good idea to install a strainer before the circulator, as some dirt may get disturbed at the bottom of the steam boiler with the circulation of water. We want to keep the debris out of the circulator, radiation, and/or IWH coil.
The use of a check valve is recommended
When doing heating only, I would suggest a bypass around the boiler from return to supply to keep too hot water from going to the radiation and flashing in the radiation. If you are using only an indirect water heater, no bypass is required.

IWH and Baseboard on the same level as the boiler

If the heat or an indirect water heater is on the same level as the steam boiler, you can pipe it as usual. Refer to the boiler manufacturer's instructions for guidance on selecting the correct boiler taps for the supply and return pipes from the radiator.

This application would not require the use of a pressure relief valve on the heating loop or expansion tank due to piping being open to the boiler.

This application is used when you want DWH Priority

This application is used when you are not prioritizing DHW

This would work for the water heater or the basement hot water loop, or both at the same time. It is essential to ensure that when the supply pipe leaves the boiler, the piping slopes downward near the floor. Keep the circulator(s) as low as possible to keep steam from entering the water loop and ruining the circulator.

Wiring IWH and/or wet heat zone on steam boiler

Control wiring - IWH to steam boiler no Priority, boiler is large enough to do both heating and IWH at the same time.
Priority Control wiring - IWH to steam boiler using a Taco SR501 relay and L6006C aquastat to create DHW Priority
Priority Control wiring - using a Taco SR502 multi-zone using priority switch.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, and installations should be reviewed on a per-job basis. Any work on your heating system should be performed only by qualified, experienced personnel. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property, or bodily injury resulting from the application of information found on this website, as a professional should review it.