You have undoubtedly noted the creep of computer technology into most everyday home appliances. Everything has digital displays, clocks, menus, etc. that allow varied cycling options. These purportedly provide finite control over the appliance function (and yet another clock to blink 12:00 forever or to be reset after every power failure).

The exception is your heating system. Home appliances are typically “closed-loop” systems, i.e. they execute a task in a contained environment.  However, if there is a digital display on a boiler, it is of temperature, operation status and failure modes as applicable. Furthermore these appear predominantly on gas-fired vs. oil-fired boilers. Why? They indicate boiler control system conditions only, not the performance of the total system, and they can’t.

Hydronic (hot water) heating systems are comprised of two elements, a hot water generator (boiler) delivering to a distribution network (radiation, heaters, zones, storage tanks, etc.) that may exhibit infinite characteristics and combinations under varying climatic conditions and demands. Try to specify a boiler for any existing distribution network as a replacement item and you quickly realize that it is virtually impossible to “get it all right”. Reviewing our other blogs you will note the amount of effort given to remedying distribution network issues, particularly on existing installations. Headaches!

Each zone (task) in a hydronic system must be supplied with the correct flow rate (gpm) of heated water for best performance. Currently this can only be done correctly with a properly sized circulator for each zone. The multi-zoned circulator distribution system is therefore the preferred option.

But what can we do with single-circulator, multiple zone valve systems? The short answer is that they by design can do nothing well. Their attraction has been initial cost offset by energy, performance and maintenance costs over system life. In fairness though, on smaller two (2) to three (3) zone systems they can perform respectably, if not perfectly.

Ironically, the direction to an efficient, reliable and cost-effective hydronic heating can be the single-circulator, multiple zone valve systems we just scorned — but with a very different circulator and very different zone valves!

First and foremost a hydronic (hot water) boiler must be sized (capacity) to match and at worst case nominally exceed the heating demands of the total structure. (Refer to our blogs again.) This value must be determined through measurement and with the use of a Heat Loss Calculator. This value and this value only can determine the properly-sized hydronic boiler for your application. (Note: We specify and use Weil-McLain Ultra Series products exclusively, but we are terribly biased!) The links are:

It should be readily apparent that the objective is to supply the ideal amount of heated water to each zone, appliance or storage tank according to its current demand. This can be accomplished by delivering the varying demand of heated water through an “intelligent” circulation system.

There are two (2) variations of these, employing different principles:

  1. The Delta-P Method (Δ-P) where P = Pressure: Employs a full-demand capable conventional circulator pump configured within a by-pass loop containing a mechanically variable Pressure By-Pass Valve. Operationally the pump operates at full capacity providing the pre-set pressure delivery while returning the excess delivery to the boiler. We recently installed one of these systems. Works well so far, but a lot of pipe-fitting required and a continuous, full powered circulator.
  2. The Delta-T Method (Δ-T) where T = Temperature: Employs an “Intelligent” Circulator on the output of the boiler that infinitely regulates delivery by maintaining a pre-set temperature differential between the supply and the return sides of the distribution system. Two (2) Temperature Sensors strapped to the supply and return lines near the boiler control the circulator speed (delivery rate). We recommend the Taco Delta-T Circulators found at this link:  Note: Significant energy consumption reduction and savings with high reliability.

Note: We strongly favor the Delta-T Method and thus the impetus for this blog.

The other half of the Intelligent Hydronic Heating System is the Zone Valving that should be mounted beyond the System Circulator, after the air eliminator/air scoop at the end of the supply manifold. These should be Standard or Full-Ported Ball-Style Zone Valves only!

Note: We strongly recommend the new Taco Zone Sentry® Zone Valve Series. Link: Featuring:

  1. Standard port ball valving to maximize flow at low resistance.
  2. Quicker actuation.
  3. LED status indicator.
  4. Lower energy consumption.
  5. Manual over-ride capability.
  6. High reliability.
  7. Low cost.

Let’s define the specifics of the common system scenarios:

  1. New System Installation – Configure exactly per our prior discussion and details.
  2. Full Existing System Upgrade
    • Resize and replace boiler with newly sized and configured unit.
    • Replace all existing circulators and zone valves with specified full-port valves.
  3. Partial Existing Zone Valve System Upgrade
    • Resize and replace boiler with newly sized and configured unit.
    • Remove Distribution Circulator.

System Design Notes:

  1. Intelligent Boiler Systems necessarily use “Cold Start” Hot Water Only Boilers. DHW Coils cannot be accommodated and therefore Indirect Water Heaters are typically used for domestic water heating efficiency.
  2. System Circulators employed by design in Condensing Gas and Multiple Boiler Systems must be retained! The Intelligent Circulator must be added to the distribution supply line outside of the “System Loop” that maintains through-boiler circulation. READ AND FOLLOW YOUR BOILER MANUAL SPECIFICATIONS!
  3. Delta-T Circulator selection is crucial not only for thermal flow capacity to match the boiler output, but for head (effective resistance) of the total system. Larger, multi-level systems need particular attention in this regard. Over sizing the circulator to either or both parameters carries a cost penalty. Under sizing will quickly exhibit a performance penalty.

The Delta-T System by design provides controlled, heated water within a pre-set, adjustable range to all distribution elements of a hydronic system. Moreover it does this irrespective of the number, size, duration and function of the distribution elements and their infinitely variable demand patterns. In so doing it becomes in effect a “self-balancing” system, eliminating hydronic noise (whistle) from over-driven zones while minimizing heating lag resulting from under-driven (lazy) zones.

The value of a Delta-T System as a diagnostic tool, particularly as a replacement system upgrade should not be under-emphasized. If it doesn’t fix or improve existing distribution issues, it surely will point out any other deficiencies and isolate them for correction. As a radiation assessment tool in particular you can now properly balance rooms using the radiation dampers, and if not identify and supplement radiation as necessary.

To summarize, it’s a terrible system:

  1. Terribly simple
  2. Terribly efficient
  3. Terribly inexpensive

Note: The Delta-T Circulator with its built-in controls is about three times that of a conventional one, and you need only one.