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 may be 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. They indicate boiler control system conditions only, not the performance of the total system.

Hydronic (hot water) heating systems are comprised of three elements, a hot water generator (boiler) delivering through a distribution network to radiation (baseboards, radiators, heaters, etc.) that may exhibit infinite characteristics and combinations under varying climatic conditions and demands. Specifying a boiler for any existing distribution network as a replacement item is a challenge 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 at an ideal temperature for best performance. Currently this necessitates a properly selected circulator for each zone. Unfortunately this method is flawed in that a “properly applied circulator” is like a broken clock and seldom correct in operation.

But what can be done 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. Hidden is the innate penalty of energy operating costs.

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. Enter the Taco Delta-T ECM Circulator and Zone Sentry 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 Boilers exclusively, but we are terribly biased!)

Next 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” dedicated circulator driven 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 circulator runs continuously at full capacity within a closed loop, providing a preset pressure delivery while returning the excess to the boiler. We recently installed one of these systems. It works well, but additional pipe-fitting and valving require continuous, full powered circulator energy consumption.
  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 preset 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). The Taco Delta-T ECM Circulator previously linked above excels in this regard.

Thus we strongly favor the Delta-T Method that is key to the development of our patented “Neo-Gravity Delta-T ECM Hydronic Heating Appliance.

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. We strongly recommend and use only the new Taco Zone Sentry® Zone Valves (linked above), featuring:

  1. Well ported ball valving to minimize flow resistance.
  2. Quicker actuation.
  3. LED status indicator lamp.
  4. Very low energy consumption.
  5. Manual over-ride capability.
  6. High reliability.
  7. Lowered cost.

Let’s define our two (2) common “appliance” system installation scenarios:

  1. New System Installation – Merely position, adjust and complete per your design specifications.
  2. Full Existing System Upgrade – Ideally locate and orient appliance for efficient replacement installation, then “stretch the pipes & wires”, as we quip. The appliance incorporates over 95% of typical system replacement materials. Just add the pipes & wires.

System Design Notes:

  1. Intelligent Boiler Systems typically use “Cold Start” Hot Water Only Boilers. Immersion-style DHW Coils cannot be accommodated and therefore Indirect Water Heaters are typically used for domestic water generation 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 “Boiler Loop” that maintains through-boiler circulation. READ AND FOLLOW YOUR BOILER MANUAL SPECIFICATIONS!
  3. Delta-T ECM 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. Nominally over-sizing a Delta-T ECM Circulator will incur little penalty due to its innate efficiency and flexibility. However, under-sizing it will quickly exhibit a performance penalty.

The Delta-T ECM System by design provides controlled, heated water within a preset, 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.

Note: The Delta-T ECM Circulator with its built-in controls costs about three times that of a conventional one, but you need only one and it pays back on energy consumption too.

The value of a Delta-T ECM 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


We encourage you to view our Patented Delta-T ECM Hydronic (FHW) Heating Appliance on this site for additional detail.

Ed. Note: Updated 03/29/2023

About the Author

Paul Mercier

A Semi-Retired Manufacturing Process Development and Hydronics Engineer.
Following a stellar career in Computer Hardware & Software, Miniature Ball Bearing, Avionics & Panel Meters, Magnetics, Plasma, IC & Discrete Component and Product Manufacturing throughout New England, have re-focused on a second, parallel skill set in Hydronic Heating.
Received U.S. Patent 10,690,356 on an "ENHANCED CONVECTION, DIFFERENTIAL TEMPERATURE MANAGED, HYDRONIC HEATING APPLIANCE". It is America's first, true Hydronic Heating Appliance, enabled by Taco Delta-T ECM Hydronic Circulation coupled with our proprietary near-boiler piping system. The resultant is a simple, durable and efficient hydronic heating appliance that surpasses all contemporary built-on-site systems both in value and performance.

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