Flexibility is one advantage hydronic floor heating has over forced air. According to John Siegenthaler, author of Modern Hydronic Heating, the underfloor heating tubes can be designed to work with nearly any other hydronic heat delivery system, as with the multi-load, multi-temperature hydronic system shown here.

The system uses the latest form of temperature control for the floor heating circuits--variable speed injection mixing. The colder the outdoor temperature, the faster the injection circulator "injects" hot water into the distribution circuit serving the floor. Siegenthaler says this approach is substantially less expensive than a four-way motorized mixing valve, yet offers the same control accuracy. In fact he sees it as eventually replacing four-way mixing valves.

The design also makes substantial use of primary/secondary piping loops. Each load has its own secondary loop, and the primary loop's only function is to feed them. This permits each load to operate under a different flow rate and pressure.