Plagued with a part of your home, a room, a heater that just doesn’t heat the way you might like it to?

    First let’s be assured your system is able to work as it was designed. Make certain that your baseboard registers, radiators, wall or toe heaters are free of lint, hair and objects placed immediately in front of them.

    1. You must take the trouble of removing the front covering and the movable damper off your radiation to expose the fins for a good cleaning. Use either a long bristled cleaning or a small diameter soft wire brush to completely remove all lint, hair, etc. between each fin. Reassemble with the dampers fully opened.
    2. Similarly remove the grilles or covers from heaters and do as above.
    3. Radiators are easier with a conventional dusting brush, but make sure it isn’t being used as a warming shelf. This will reduce efficiency.
    4. Did you note any fittings with a screwdriver slot or small cans with a stem cap on top at an end of your baseboard registers or near the top of your radiators? These are vents and must be opened until a steady flow of water is emitted. On the automatic “can types”, the vent cap (looking like a tire stem cap) must be removed and the stem depressed to confirm a water flow. Replace the cap and leave it very loose to allow air escapement in operation. If repetitive can venting is required or stem leakage is observed, replace them as faulty.

    Notes: If any vents don’t allow water flow or leak thereafter they must be replaced, probably by a technician (unless you know how to remove boiler pressure, or get wet swapping without doing so). If your baseboard radiation has no vents you have a newer system that requires “purging” at the boiler, and probably by a technician. (You must isolate each zone by closing valves and forcing water through each piped heating zone to force air out of that system area.)

    All of this is just to assure that we have a water-filled system and good radiation integrity, bringing us back to what your system was designed to do. Now we can detect system flaw(s) without guesswork.

    Switch on your boiler with all thermostats turned down or switched off. Turn up one thermostat and note the warm up of its zone radiation. Does all radiation warm up quickly along the piping flow direction and is evenly tempered? (Hold you hand near each register to sense.) A cooler radiation fin area denotes probable air entrapment. Vent or purge as necessary. Similarly with toe and wall heaters. Do their fans switch on after temperature rises significantly? If not, vent them again. Same? Read on. Balance the temperature of each room in the zone by leaving the radiation dampers or radiator valves in the coolest room(s) FULLY OPENED. Progressively close downward the warmer room(s) dampers or valves until the desired balance (or imbalance) of temperatures is achieved. If you can’t achieve the desired balance, adding radiation to the coolest room(s) may be required.

    Repeat this procedure with all zone thermostats and take notes as required.

    Please note that we have optimally tested each zone individually, and in succession. Now we must analyze the entire system in operation.

    If you have only one heating zone (one thermostat) in your home, the following discussion is probably moot if you noted no major issues in the system clean up and venting/purging.

    Circulators are the method of choice in modern hot water (hydronic) distribution. Every system must have at least one. They circulate heating water quietly and efficiently. The question becomes whether they are performing adequately.

    For any structure having more than one thermostat (zone) there are two circulation options:

    1. Each zone has a dedicated, thermostatically controlled circulator.
    2. A shared, single system circulator is used, with individual, thermostatically controlled zone valves switching each zone.

    Being the common distribution component to any hydronic (FHW) heating system, THE CIRCULATOR MUST MATCH THE TASK IT IS REQUIRED TO PERFORM! Whether it is the single System Circulator or the multiple, dedicated Zone Circulators it must move an adequate amount of heated water from the boiler through your radiation.

    The scenarios are therefore:

    1. One or more circulators dedicated and matched to their respective zones.
    2. One system circulator matched to boiler and/or total radiation capacity shared by all zone demands.

    The dedicated zone circulator scenario (No 1.) is by design self-regulated. (Radiant Heating zones must also be served by dedicated circulators.)

    By design a shared system circulator cannot be all things to all zone valved radiation zones at all times. The question really is whether it really matters during the course of normal operational demands. The answer is that it depends on the individual zone configurations, their size and content.

    Zone symptoms to look for:

    1. Baseboard and particularly radiator temperatures that decrease significantly as you move from the supply line (off the top of the boiler) pipe through the radiation sequence to the return line (going toward the bottom of the boiler). This can explain rooms that warm up slowly or always seem cool, even with radiation dampers or radiator valves fully opened.
    2. The kitchen kick space (toe) or wall heater that seems to vary in temperature output and sometimes runs cooler, short cycles.
    3. The large downstairs and/or upstairs zones that don’t warm as quickly as others during a cold start up (Programmed thermostat setbacks or a cold boiler restart from an emergency switch.)

    All of the above are symptomatic of low zone circulation conditions that can only be improved by qualifying each zone circulator(s) or system circulator size for zone valved systems. The sure check is to measure the temperature difference between the input (supply) and output (return) near the boiler of each zone with a thermometer or thermal crayons. The narrower the temperature difference the better, with a 20 degree drop being ideal.

    So, if you have a smaller house with similar zones and no significant symptoms, disregard this. Otherwise you may wish to consider a move to correctly sized circulators, remembering that the most often found issue with them being incorrect (too small) sizing. That little green Taco 007 Circulator that is used almost universally and sold at the local hardware or ‘box” store just can’t do everything everywhere.

    To summarize:

    Zone valves coupled to a correctly sized system circulator provide a viable, economical solution to a modestly sized, similarly zoned home. Their installation and repair costs are lower than circulators, but repair incidence varies with cycle times. The system circulator necessarily has a very high cycle time, reducing its longevity. A system circulator failure completely shuts down your heating system operation. Upgrade your Green and Gold Head Zone Valves to the new “energy green” Zone Sentry Valves for performance.

    Properly sized, dedicated circulator zones offer constant, efficient distribution. Dedicated circulators are a moderate cost additive yet are much less prone to failure.

    Improperly configured or piped zones are also a consideration, particularly with zone valves. The possible deviations are substantial and are therefore not included in this discussion, save to consider this possibility if the discussion scenarios do not correct your situation.

    Taco Service Notes:

    1. If you currently still have Taco “Green Head” Zone Valves in service, you may wish to upgrade them to the newer, interchangeable “Gold Head” Actuator. They are simple to change, merely a clockwise 1/16 twist of the head and they are off. Rewire per the prior Head.
    2. If you have any old style circulators (separate motor, coupling and pump assembly with oil fittings on the pump and on some motors) consider upgrading them to the newer “Wet Rotor Circulators”. They are a smaller, integral design that runs in the heating water. Far more efficient, reliable and service free. Made by Taco and others. Make certain to correctly size the substitute.

    Refer to the Blogs on our “Delta-T System™”. It is the final solution.

    Last Edit: 10/10/2012 pdm


    In the 1800’s steam was king! It ran the trains, industries, ships, heated the largest buildings and the finest homes. Steam heating continued in this respect into the early 1900’s to even smaller homes, providing distinctive styling and comfort to the American Lifestyle.

    Those beautiful Victorians, updated Colonials, Southern Manors, Seaside Mansions and latter day Bungalows were all heated by steam as the method of choice. They featured ornate radiation and huge central boilers fired by coal, cotton waste, corncobs, peat moss or wood — and lots of it!

    The age of cheap energy has passed and so seemingly the Age of Steam Heating ….. but not so fast! There is an old adage of “throwing the baby out with the bath water”, cautioning us to not dispose of the good to rid us of the bad. This aptly applies to steam heating in our opinion.

    The simplicity and comfort level of steam heating is unarguable. Those well placed, aesthetic and space efficient radiators emit both heat with a light hiss of escaping steam simultaneously heating AND humidifying our air. Room temperature can be reduced somewhat without a comfort penalty. To duplicate this environment requires mechanical creation using power humidifiers or more complicated HVAC Systems. (That’s also why common homes had a tub of water on the heating stove.)

    Three usage factors affect steam heating:

    1. Fuel efficiency. Those old steamers have heat exchanger passages and flue pipes intended for large, continuous combustion, low temperature fires that are the polar opposites of small passage, high temperature oil or gas fired systems.
    2. Installation or repair cost. Residential steamfitting is one of those fading (and therefore expensive) arts, it seems.
    3. Flexibility. Those big iron pipes don’t stretch or move readily. Extending a system seems formidable.

    Not so fast, again!

    You may have noticed that virtually nothing ever happens to the radiators and piping in your system — the distribution side of things. Yes, a radiator vent may stick so it can’t be adjusted. So you unscrew it (with the steam turned down) and replace it. A valve stem leaks, so you tighten or pack it. Unlike hydronic systems, no gurgling, noisy, tinny registers, circulators, relays or vents to go bad. Steam provides the absolute in physical non-mechanical distribution simplicity, efficiency and durability. This is the “baby” in our analogy.

    The “bath water” is that beast of a boiler — the dinosaur. This is where virtually all of the efficiency gains are to be had (plus a little smart usage). Additionally, this is where the third factor (flexibility) must be introduced and discussed in common.

    A steam boiler is like putting a partially-filled pot of water on the stove with a perforated cover over it to let steam escape in a controlled manner. When you turn on the stove the water rose in temperature until it generated steam. If you don’t need steam the water in the pot is still hot in degree and usable heat. There are therefore two usable components in a steam boiler — hot water and steam. As in past steam systems you can employ the hot water component to provide domestic hot water and additional forced hot water zone heating. So if you want to stretch your steam system to heat the garage or that added room, it’s available.

    That big iron hulk down there was designed with complimentary, rather large distribution piping. Hopefully at some point or through your efforts heat loss of the building has been improved. You don’t need the distribution size as a result. This is not necessarily a detriment, however. What is more important is to not under size the replacement boiler and it’s steaming time.

    As you create steam in a boiler, the boiler water level is reduced as steam rises throughout the distribution (pipes & radiators). Steam is condensed in the radiators giving heat, and this condensate (now as hot water) cools, slowly trickling back to the boiler. If you generate a lot of steam rapidly from a too small boiler, the water level drops quickly. The low water indicator feeds a quantity of new water into the boiler by design. Then the eventual returning surge of condensate “floods” the boiler, reducing or limiting its ability to create steam (heat). Make-up water management can be important.

    Worse, in the smaller boiler scenario there is also the danger of overheating the boiler to the extent that thermal shocking can be induced by replacement water, damaging the boiler.

    There are tricks to reduce these scenarios, but there is one guideline that works every time:

    Boiler Weight (Size) and Water Capacity = Performance Efficiency with Longer Boiler Life (Just look at the unit you are replacing.)

    We invite you therefore to compare the weights and capacities of Weil-McLain Steam Boilers with all of its competitors.

    If you are still determined to be rid of the old steam system in entirety, so be it. But save back those radiators. Don’t give your installer an extra payday.


    While recently taking delivery of a large Weil-McLain Ultra Oil Boiler, our distributor’s driver commented: “I hate to deliver these boilers, they are so (mild expletive) heavy compared to the Buderus and the other ones.” (This large distributor markets several popular product lines.) The driver’s comment became evident when three of us were needed to tip up the crated boiler dolly in the truck, then four to move it into the building. (The driver normally handles it himself in the truck and then another or two assist him to transit into location.)

    This experience prompted us into a little research that confirmed the driver’s observation. Yes, the Ultra Oil “high-mass” is much heavier than its “low-mass” competitors — by 100 to 250 lbs at minimum for the equivalent firing rate (capacity). As Heating Engineers we also appreciate the design integrity of this new, FEA (“Finite Element Analysis”) designed boiler “block”. It is a “beautiful beast” in a very complimentary fashion, both in performance and serviceability.

    As a lifetime “motor head” (car performance enthusiast) the analogy came immediately. “It’s a Hemi!” The original Chrysler Hemi(spherical) Engines of the 1950’s and beyond dominated Drag Racing and other racing forms. Originally designed as an Industrial & Marine Engine, it was big, heavy, durable and ultimately very powerful. A modified 180HP automobile motor readily became a 1500+HP racing motor.

    So what does this have to do with boilers? Boilers are heat engines in the purest sense of the term. They ignite and burn fuels to efficiently generate hot water (or steam) to warm our living environment. In an automobile heat not converted into mechanical power is wasted. The boiler meanwhile is all heat generation and tempered distribution.

    Harnessing heat energy also entails risk. (Boilers are necessarily constructed of “sections” with seals between them. Picture a loaf of bread made up of “slices” with “crusts” at each end.) Controls manage this process but may not ultimately protect the boiler from damage under some circumstances, namely:

    1. Water contains minerals and contaminants that generate an acidic sludge in the bottom of boilers (and piping). (Open your boiler drain valve to confirm, if you dare.) Sludge corrodes, eating cast iron and in particular steel plate boiler weldments, reducing boiler life and heat exchange efficiency. Doesn’t help the seals either.
    2. A damaged combustion chamber may permit direct firing onto heat exchanger surfaces creating “hot spots” that create thermal shocking and failure conditions.
    3. Introducing cold water into a hot boiler thermally shocks it. It can occur even during normal operation when large, cold-water heating zones are suddenly demanded into a hot boiler. The metallurgy of the heat exchanger changes, embrittling it to ultimate failure by cracking, warping the section(s) and causing internal seal failures. These situations can be catastrophic.
    4. Using anti-freeze compounds. Many manufacturers, particularly of older boilers, prohibited their use. Newer seal materials have limited the risk. However, check your Warranties! Even using the recommended anti-freeze increases leakage potential in the system. (Servicemen generally dislike its use.)

    Summarizing: Cast Iron and Water Volume = Increased Boiler Life and Performance (Simple Physics)

    The boiler operates at a lower average temperature and accommodates load and surge conditions more readily with no efficiency penalties.

    May we suggest that a high-mass boiler is also a better value?


    This Blog, originally written in 2008 has been superseded by our subsequent development activity, culminating in a Non-Provisional Intelligent Property Protection Submission (Utility Patent) in the USA & Canada in April, 2017.

    The original blog crossed out text following has been retained to witness our efforts in both timeline and content. The final submission attributes:

    1. A true hydronic appliance vs. the partially pre-built, conventional system described therein.
    2. New Delta-T ECM Hydronic Technology is fully integrated, dramatically reducing component content, increasing distribution efficiency and system performance.
    3. Gravity (Convection) Heating is optimized and provides innate, additional performance.
    4. A flexible, modular design, it is readily manufactured and provides excellent value with predictable performance.
    5. Prior and further proprietary design features have been fully integrated. Example: The “Iron Cross Manifold” has evolved into the “Compact Steel Hydronic Header” – Patent Pending.

    The ENHANCED CONVECTION, DIFFERENTIAL TEMPERATURE MANAGED, HYDRONIC HEATING APPLIANCE™ Product Brochure on our BoilersOnDemand.com website will further detail our effort. 

    Amended 07/07/2017 P.D.M., Sr.

    Modern, high efficiency hydronic (hot water) heating systems necessarily incorporate technological features that sophisticate them, particularly in the areas of controls and distribution. Whereas in the past one could make a few wiring connections and connect a few pipes, now the task may appear daunting. However, organizing these functions logically and employing selected hydronic and control components can result in both a sophisticated, yet simple system.

    Mercier Engineering is dedicated to advancing hydronic heating applications by applying the benefits of over 50 years of “being in the trenches”, so to speak. As such we recognize that there are skilled DIY’s (Do-It-Yourselfers) and Contractors who have access to skills complimenting heating installations. Our contribution is to reduce the task to a manageable one in cooperation with our customer by providing a very cost-effective, packaged forced hot water heating system.

    Since the introduction of Weil-McLain’s Ultra Series of Gas and Oil Boilers (click on our site links) and applying Taco’s renowned hydronic components and relays to them, we recognize the opportunity of readily “packaging” these products. This is further highlighted by the recent announcement of our “Iron Cross Manifold” (TM) System that efficiently configures multiple circulators and valving. Furthermore as service people ourselves this configuration is a serviceman’s pleasure, providing ready access and diagnostics for future eventualities. Note that this service is available ONLY on and limited to the Weil-McLain Ultra Series Products.

    From client supplied site detail we build the boiler systems on the Weil-McLain Pallets, then knock them down for re-shipment. All shipments are F.O.B. Antrim, New Hampshire. Note that packaging limitations may preclude commercial freight and require arranging local pickup by the client.

    To complete the installation the client will have to:

    1. Transit, de-palletize and position the system.
    2. Exhaust the boiler per manufacturer recommendations.
    3. Assemble the burner to the boiler (oil only).
    4. Extend fuel connection (gas piping or oil line) to the system.
    5. Extend 1/2″ water service to the input pressure regulator/backflow preventer.
    6. Connect the heating zone supplies and returns as applicable.
    7. Connect the thermostats to the control relay.
    8. Extend 110V 15A power service from the overhead thermal switch to the boiler service switch.
    9. Execute system fill, purge and start up procedures.

    Also note that all permits, code compliance and inspection(s) are the responsibility of the client.

    So, if you have been hesitant to upgrade and thought you just couldn’t afford a top-end Energy Star System, but have complementary skills at your disposal, this may be an answer to your dilemma.

    Contact us to discuss your particular situation. As usual there is NO OBLIGATION.


    Mercier Engineering announces that of this date, July 19, 2008 it will heretofore refer to and claim origination of its unique hydronic piping configured supply and return manifolds based on the use of pipe crosses as an “Iron Cross Manifold™”.

    Further, all of Mercier Engineering’s subsequent designs, build and install boiler configurations will employ the “Iron Cross Manifold™” as a product performance enhancement feature wherever applicable on supply and return piping configurations.

    To date this technique has been employed specifically on overhead multi-circulator supply and single point purge return manifolds, some of whom are pictured on this site. It has corresponding benefits as well with zone valve based systems that we intend to incorporate into our designs.

    As background we offer that Mercier Engineering has been developing practical and durable black iron piping configurations specifically for the unique and efficient Weil-McLain Ultra Oil “Triple Pass” Boilers in an effort to maximize their performance while improving installation practice for improved economic benefit. The resultant is a structurally superior, durable, flexible, very serviceable and efficient alternative to the usual copper pipe built-in-place installation practice. To this end our boiler replacements have used minimal to no, and yes have in fact netted surplus copper pipe! That cost benefit alone is currently notable.

    Mercier Engineering has focused on Weil-McLain’s Ultra Oil Boiler, but the “Iron Cross Manifold ™” is applicable to their Gold Oil and Ultra Gas Series as well. It is our intent to provide these applications ONLY. We are exclusive to the Weil-McLain Product Line and will remain so for the foreseeable future.

    See also our Pre-Built System announcement.


    Water heaters are rated by the number of gallons of water per minute (GPM) or per hour (GPH) that they can raise water 100 Degrees Fahrenheit. This measure applies to all water heaters, regardless of their construction or fuel source.

    So by definition if we can increase the incoming water temperature to our heater:

    1. The output water temperature can be increased (subject to a safe temperature limiting), or
    2. The volume of controlled temperature water output can be increased, and
    3. The total effective capacity of any heater can be increased.

    Domestic water entering your home (or business) is always significantly colder than the heated environment. Thus as an example you must let the water run a while before it gets cold to pull cooler water from the outside the building (underground) water source. The effect is similar with the hot water heater supply piping, subject to the limited water piping capacity within the heated area. When the cooler water reaches the water heater it has to work harder to elevate temperature. Therefore by increasing the amount of environmentally warmed water to the heater we increase performance and save energy.

    Placing a non-insulated water tank between the water service entrance and the water heater allows a larger volume of water to acclimate (temper) to the ambient temperature at its location, thus a “Tempering Tank”. Its construction and configuration are simple:

    1. A somewhat taller than wide tank with two pipe openings, one near/at the bottom and the other near/at the top. Its interior finish must be compatible with passing potable (sanitary) water through it safely.
    2. The incoming (cooler) water is piped to the bottom of the tank and the outgoing (warmer) from the top to your water heater. Hot water rises and therefore the warmer water stays substantially at the top while the colder replacement water enters the bottom. Water will diffuse within itself, but at a typically lesser rate than used, protracting this effect.

    Practically, any water heater or water storage tank stripped of insulation and being glass, stone or otherwise lined for water cleanliness is suitable. There are other options as well, typically used for well pumps and wet processes. So, look around for an opportunity.

    Note: One point to remember is that the temperature differential and flow of cold water can cause these tanks to “sweat” (condense moisture on the lower exterior of the tank). The simple solution is to provide a larger pan with an inch or so of coarse sand in it under the tank to absorb and then evaporate the condensation effectively.

    Please accept that this is not a cure all for a too marginal heater or a plugging in-boiler or other heater coil. The latter will surely get worse over time, but in the meanwhile helps with comfort while saving energy.

    This “trick” is nothing new. We sometimes refer to them as “Farmer’s Tanks” when found in our older New England Homes. Thank them.

    It’s a great Do-It-Yourself (DIY) Project. So that old electric water heater with the burned out elements that you just haven’t disposed of yet may have some life left in it after all.

    Last Edit: 04/05/2017 pdm


    During the heating season, having an Immersion Coil in your Boiler to provide Domestic Hot Water (DHW) makes a lot of sense. You are utilizing the hot water present in your boiler for area heating to additionally provide hot tap water at a very reasonable cost.

    But what about when there is low or no area heating demand? Your boiler is still hot (typically between 160 and 190 degrees F) waiting to provide occasional domestic hot water (at about 120 to 140 degrees F). Meanwhile the boiler stays at temperature, radiating heat into the boiler room and leaking heat up the chimney, neither of which can be utilized.

    A commonly used trick to save energy during the low demand period is to turn off the boiler entirely using the Emergency Switch (usually located near the main hallway door, but may vary). When hot tap water is needed the boiler is switched on and provides hot water within 15-20 minutes, typically. After use the boiler is again switched off. The really thrifty have learned to shut off the boiler before the last shower or then run the dishwasher to utilize the remaining boiler heat to advantage.

    The efficiency answer is an Indirect Water Heater, a super-insulated storage tank heated by your boiler and substituting for your Immersion Coil. The best of these are made of stainless steel, super-insulated to lose about 1/2 degree F per hour and have lifetime warrantees. Additionally your Boiler Aquastat Control (controlling boiler temperature) should be changed to a “Cold Start Aquastat”, allowing it to heat ONLY when area heating or Domestic Hot Water is demanded or used to maintain tank temperature. Your boiler is now an “on-demand” type, lowering toward room temperature between cycles.

    This storage of a quantity of heated tap water not only gives you instantly available hot water at any time but is inexhaustible, with your boiler cycling to meet any demand. No more initially hot water that cools down quickly with use caused by under-sized or sediment-clogging Immersion Coils either. Yes, the thrifty can still use the Emergency Switch trick for additional savings. In fact, one family of four with two young boys has found that they need only switch on every two days in the summer after several showers, dishwasher, wash the dog, etc.

    Your boiler runs less and runs cooler on average too, prolonging its life while reducing radiated and chimney drafted heat losses. Efficiency gains all around.

    Note: This argument also applies to separate Electric, Gas or Oil Hot Water Heaters by incorporating them into a managed, single fuel system.

    Last Edit: 10/10/2012 pdm