Conventional boiler controls produce one temperature of heating water, a temperature calculated to keep your house warm on the coldest day of the year. (In Boston, the coldest day’s temperature, or design temperature, is between 9 degrees and 0 degrees F.) Each winter, the design temperature is reached for only a few days and sometimes only for a few hours, but the boiler operates with a water temperature to match this outdoor temperature for the entire heating season, a season in New England which stretches from October to April (or May). Weather sensitive or outdoor reset control on your boiler allows the boiler water temperature to modulate with the outdoor temperature.

Every three degree drop in boiler water temperature equals a one percent fuel saving, so using outdoor reset saves substantial money. For example, if it is a 0° F. design day outside, your boiler will produce 180°water. When the temperature warms to 40°, an outdoor reset control will allow your boiler to produce 150° water, a drop of 30° in water temperature or a ten percent fuel saving.

Outdoor reset controls can be added to your system at any time and do not require the system to be drained. Sensors are added externally and the initial cost is for the control and the electrical wiring. We recommend adding reset to almost any existing forced hot water heating system for immediate fuel savings, system comfort, and efficiency.

Heating system circulators, or pumps, move heated water from the boiler to distribution units (radiators, radiant floors, baseboard, or hydro-air heating coils) and then back to the boiler again. When we design a heating system, we select a circulator that can move the maximum amount of heat- carrying water needed by the building (or portion of the building served by the pump) on the worst day of the winter. But pumps do not come in an infinite number of sizes and also do not come in very small sizes, so we often have to choose one which has more capacity than necessary. Also, the heating needs of a space change depending on many things, including the outside temperature and time of day so the maximum capacity of the pump might only be required a few days or hours a year. Until recently, the pump could only draw electrical energy at one level when it was on- the maximum, over-sized level.

This overuse of energy gets even worse in systems with multiple zones, each served by its own pump. The zones are often small pieces of the whole space’s heat loss, and the smallest pumps available are capable of covering the whole system, so each zone multiplies the overuse of electrical power.

Pumps are now available with ECM (electrically commutated motors), which allows them to change their electrical draw according to the demands of the heating system. When all zones are calling for heat, the pump uses as much energy as necessary to circulate the large load. As zones are satisfied and drop out, the electrical draw also drops. The pump is essentially customizing itself to the system. In a multiple zone set-up, the ECM pump can save thousands of dollars in its lifetime. This is why we choose to pipe our customers’ zoned systems using a single ECM pump and zone valves, rather than pumps on each zone.

Zone valves are motorized valves which open and shut when the zone thermostat instructs them to. They are available with easily replaceable operators and have good reliability. Manufacturers like TACO make relay boxes which allow all the wiring for zone valves to be organized in one place with the proper transformers. The boxes have indicator lights that allow us to track the progress of a call for heat in each zone.

NON-ELECTRIC THERMOSTATIC RADIATOR VALVES or TRVs are devices which can be added to a steam or hot water radiator to control temperature at the individual radiator. A wax element in the valve expands and contracts with ambient room temperature, opening and closing the valve to maintain whatever temperature is set on the operating dial. These devices are useful in control of over-sized or overheating radiators, as they shut the radiator off when the desired room temperature is reached. They are installed between the radiator and air vents on steam units and in place of the hand valve on hot water radiators.

Rooms can be individually zoned simply by installing trvs on their radiators. The operating head of the valve can be placed directly on the radiator or the valve can be operated remotely with a wall-mounted dial, attached to the valve via capillary tube.

Heating zones have been touted as energy saving measures, and many customers have shown us their multi-zoned systems, proud of the number of zones they have. But when we look at how the house’s space is divided and used, the “zoning” is often nonsensical. Sometimes the installer has “zoned” in the easiest way the piping will allow. Old gravity heating mains, for instance, were often piped left and right side, or front and back through all the floors in the house, to shorten the distance the water had to travel to and from the boiler. An installer may say he can zone using the existing piping, but it makes no sense to have a left and right division. Customers have been sold zoning for an upstairs and downstairs scheme, but once their children can go up and down stairs themselves, the temperature in the living room and the bedrooms will stay the same as people move back and forth while they are awake, and then the whole house temperature will be lowered when the family goes to sleep. We have customers in whose homes there may be seven programmable thermostats on seven zones and all of them are set to come on and turn off at the same times and temperatures. That is actually one zone with seven expensive control systems stuck onto it.   What is the point of a zone?  Zones need to make sense with the way the house is used, but they have to obey the laws of thermodynamics as well. If the zoned rooms can’t be thermally isolated from one another, there is no point in pretending the btu’s will stay in their respective areas. Heat goes to cold no matter what. You may turn the thermostat down in the dining room, but if there is an open archway between it and the living room, the living room zone will attempt to heat the dining room as well. No savings -in fact, lost money in the equipment wasted in setting up the “zones”, and plenty of discomfort in the drafts caused by wandering btus. A third floor guest room with a door that stays closed, or a basement family room isolated by the cellar door can be zoned successfully- the temperature can be set lower than the occupied part of the house and it will stay that way. Another reason to set up a separate zone is to accommodate heating units with different heating qualities which would not work well together on the same thermostat- for instance, a main house with cast iron radiators and a playroom with fin-tube baseboard. The cast iron will heat more slowly and hold its heat much longer than the fin-tube. If the thermostat is in the room with the radiators, the baseboards will be cold as soon as the thermostat turns off. Put the thermostat in the playroom and the radiator rooms will overheat.   The final factor in deciding whether and how to zone a heating system is the effect of the zones on the boiler’s efficiency. The most efficient way for any boiler to operate is in long runs where the boiler can reach its steady state. Think of a car’s mileage when it is cruising on the highway, vs. stuck in stop and go traffic. Having a system with many small zones can cause a boiler to stop and go, or “short cycle”. If one little office or bathroom is asking for heat, the boiler (sized for the whole house) will quickly make that heat and have to shut down, and the process will repeat itself until a larger space asks for heat. Even a modulating boiler, which is designed to drop its firing rate when less output is required of it will short cycle; there is a limit to how far the boiler can turn itself down. Combining unnecessarily chopped up zones into a larger load can remedy a short cycling problem. On a new installation, fewer zones will have a lower upfront cost and will operate more efficiently over the lifetime of the system than multiple small zones.   See discussion of outdoor reset controls, air sealing and insulation and alternative ways to make domestic hot water for other tools to save energy.