• Tag Archives Circulator Sizing

    Periodic discussions with Do-It-Yourselfers (DIY’s) prompt the subject of heating loops (radiation piping). In particular Steam-to-FHW Boiler Conversion inquiries inevitably ask “how do I pipe my old radiators if I want to keep them?” A good time to review distribution piping.

    We must preface by stating that traditional perimeter “fin tube” radiation loops are the simplest and most efficient means of heating a structure. They lessen piping lengths, head pressure (flow resistance), minimize material & labor costs and require less circulation (distribution) energy. Beware the contemporary plumber or heating installer who claims that all of his additional “pretty piping” and controls increase performance. To the contrary! Be aware that powered air handlers, cabinets and radiant heating loops all require significant additional hydronic and electrical energy.

    There are three (3) common variations of heating loops:

    1. The Series Loop – The most common configuration. Supply piping from one radiation element (baseboard, radiators, fan convectors, etc.) to another in a serial sequence and returning.
    2. The Split Loop (sometimes also called the Split Series Loop) – A larger pipe (or pair) feed to the mid-point of a series loop, supplying water to both halves and returning by individual pipes or a larger pipe, closing the loop to the boiler. A hydronically balanced circuit is necessary to minimize distribution energy.
    3. The Monoflo(w) Loop – A larger, closed piping loop that continually flows water. All radiation is teed off this “runway” loop to both of its ends, driven by a Monoflo Tee that pulls (moves) water through them by utilizing a “venturi effect” pipe tee.

    The Series Loop is simple, but maybe too simple. How can you go wrong? Pipe from one radiation element to the next and close the loop from and to the boiler. Problem is, every fitting, foot and rise of pipe = resistance to flow. Resistance equals “head” that must be accommodated by properly sizing both piping and circulators to provide even heating. (You may want to also read our blog onLAZY HEATING ZONES.) The effects can be:

    1. Too small a circulator and/or piping size results in a “lazy” zone – temperature (heat) in the first heating element to the last can drop significantly, providing uneven heating.
    2. Install too large a circulator to overcome this and you risk “hydronic noise” created by over-speeding water. Take care to not create very long piped zones as a practice.
    3. You inadvertently are loading your electric bill in either case. Longer circulation cycles in a “lazy” one or overpowering in the latter. Size and lay out zones properly.

    The Split Loop by nature is more efficient, requiring less power to move water and lessens the temperature (heat) differential across radiation significantly. It’s also a good way to get out of trouble with a poorly performing Series Loop – as long as it’s not too poorly configured. Strategically it’s also a good choice for future splitting into individual zones. Plan ahead.

    1. In new construction lay out your common feed(s) and return(s) so that you anticipate future lifestyle heating options.
    2. In old construction, re-pipe with feeds and returns to enhance current heating conditions while again anticipating future options.

    The Monoflo(w) Loop is a technique that is currently seldom used due to cost. It takes a little more pipe (and time) to configure and requires a little more circulator to drive through the required venturi tee fittings. But if you want nearly simultaneous delivery and even heating – this is it! Most often found on older baseboard or converted cast-iron radiator systems.

    There is additionally a seldom used TwoPipe, Reverse Return Method as a proven way to evenly supply larger radiators or other convectors. A dedicated supply pipe (manifold) is routed and branched to each convector. A similar, separate return pipe (manifold)  is likewise routed and branched to each and back to the boiler. Key is to return flow in the opposite direction to that of the supply, i.e. the first radiator supplied is the last to return. FILO = “First In, Last Out”. This reasonably balances delivery and lowers head pressure in a properly proportioned, dedicated supply and return “pipe manifold” system.

    We finalize with the major current application for the Monoflo or Two-Pipe, Reverse Return System, converting Steam Radiators to FHW Heating. You MUST re-pipe every steam radiator into a separately piped supply and return, then drive them either with a Monoflo Distribution Loop or a Two-Pipe, Reverse Return System. These are the only effective ways to even out any large radiator-based zone. There’s a lot of water in those radiators! Pipe them into a Series or even a Split Loop and you will soon appreciate the term “lazy” heating. So, DIY Steam to FHW System Converters in particular take note! The result is well-balanced, even heating with less, although more forceful circulator cycling.

    Know your heating loop options and do your technical homework related to pipe and circulator sizing for efficient distribution.

    Author’s Note: This discussion is predicated on contemporary fixed (single or multi-select) speed circulators. The hydronic distribution “ball game” has now totally changed with the introduction of Delta-T ECM Hydronic Circulation. It is applicable to both new and existing installations, providing dramatic electrical along with some fuel consumption reductions. We are acknowledged application pioneers of this technology and have been recently awarded a U.S. Patent, Canada to follow on our ENHANCED CONVECTION, DIFFERENTIAL TEMPERATURE MANAGED, HYDRONIC HEATING APPLIANCE. All in the quest for Simple, Durable and Efficient Hydronic (FHW) Heating.

    Last Edit: 07/17/2020 PDM, Sr.


    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