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Toe kick heater with monoflo tees in parallel with a radiator in a series loop

atulc Member Posts: 4
My house has the living room, dining room, kitchen, and sunroom served by hydronic baseboard radiators in a series loop. I'm remodeling the kitchen and the plan calls for using all walls for cabinets. I've decided to remove the 5' radiator currently serving the kitchen and install a toe kick radiator under the sink cabinet.

I was expecting the plumber to install one 3/4" x 1/2" monoflo tee and one standard 3/4" x 1/2" tee greater than 12" apart on the 3/4" heating pipe. Instead, he installed two monoflo tees in parallel with the 12' baseboard radiator serving the sunroom. the supply and return pipes for the sunroom radiator run parallel to each other, about 8" apart, through the center of the kitchen. He put one monoflo on each of these pipes in one joist bay.

Should I be worried about this configuration? Is it OK to mix and match series loop with a toe kick heater in parallel with a baseboard radiator? In all the diagrams I see online, either everything is in series or everything is in parallel. E.g., see https://www.houseneeds.com/learning-center/hydronic-radiator-installation/hydronic-radiators-convectors-piping-examples. In the middle left picture at the link above (series loop), the plumber installed two monoflo tees to serve the toe kick heater across the top right baseboard radiator.

Is this acceptable? Or should I insist on changing the configuration to be as shown in the series loop picture? I haven't installed the toe kick radiator yet. The subfloor is currently open and it's easy to do plumbing and electrical work within joist bays.


  • HomerJSmith
    HomerJSmith Member Posts: 2,309
    edited October 2019
    Normally, if the supply to the toe kick is below the radiation, you use only one monoflo tee. If the supply is above the radiation you use two monoflo tees. I put the monoflo tee on the supply side rather than the return side of the toe kick. You put at least 12" between tees, I always put 18" between tee if I can.

    I always use genuine monoflo tees and not the cast diverter tees that come from China.

    Toe kick heaters are always in parallel to the loop that supplies it. That's what a monoflo tee does, allow flo in a parallel circuit thru a pressure differential.

    I read your post 5 times and I don't quit understand it. A drawing for your setup would be helpful to me.

    If you are replacing a 5' baseboard, and I assume that the supply & return is under the floor and that under floor is accessible, you would cut out the risers and couple a straight pipe between the supply & return risers. Then you connect the toe kick to the loop.

    When hot water is passed thu a 12' baseboard, the temp on the supply drops as the water passes thu it. Your installer may worry about the toe kick is getting less hot water so he put a monoflo on the 12' baseboard which allows hotter water flowing to the toe kick. Toe kicks have a thermo disc on it the turns the fan on at about 120 deg. But, baseboard sys usually run at about 180 deg.

    You need to cut out a square the size of the toe kick on the bottom floor of the base cabinet for access to the toe kick for air elimination and repairs. You need to put an coin air vent on the toe kick at the coil level if the supply is underfloor.

    Is the toe kick going where the 5' baseboard is, between the baseboard risers or at a different location ?

  • atulc
    atulc Member Posts: 4
    Thank HomerJSmith for the detailed response and questions. I will post a sketch shortly and answer your questions.
  • atulc
    atulc Member Posts: 4
    Here is the schematic showing before and after. You will notice that one baseboard radiator was removed and piped straight through and monoflo tees were installed to serve a new toe kick heater. My concern is that this configuration is going to reduce the flow in the baseboard radiators that are now in parallel with the toe-kick heater. The plumber should have installed the two monoflo tees on the same pipe more than 12" apart.

    The two baseboard radiators at the extreme right of the schematics are a total of 12' long. I believe the toe kick heater will now reduce flow through these radiators.

    Please advise if I should have the plumber install the two monoflo tees on the same pipe (the supply side pipe for the 12' radiators) rather than one on the supply and the other on the return side of the 12' baseboard radiator.

    EBEBRATT-Ed Member Posts: 14,495
    The way the plumber did it will be fine. I probably would have used only one mono-flow tee depending on how much flow the toe kick needs.
  • atulc
    atulc Member Posts: 4
    The radiator loop on the extreme right is the coldest room in the house. It's a sunroom with windows all around. Won't reducing flow to these radiators affect the comfort in this room?

    My question is not whether the plumber should have used one or two monoflo tees. It's whether the toe kick heater should virtually be in a series loop vs. being in parallel with the sunroom radiators as configured by the plumber.
  • SuperJ
    SuperJ Member Posts: 609
    edited October 2019
    I would connect the supply and return to the top pipe (the one after the room on the right). That way the cold room gets full flow of the hottest water. Connect it in parallel with a section of pipe that equivalent in pressure drop to the toe kick. If the bypass section is shorter you could put a ball valve in to throttle and force more flow thru the toe kick if necessary.

    I think it will work as is, but it is stealing flow from the cold room since it's in parallel. The saving grace is that the cold room will see hotter water now since it doesn't go thru the kitchen baseboard first. So it may be a wash heat output wise.

    Regardless you may want to put a device in to balance the flow so the toe kick steals the minimum amount of flow.

    Luckily hotter water usually has more of an effect than more water assuming your flow rate is already reasonable.

    You see once you get above a certain flow the output doesn't change much.

  • HomerJSmith
    HomerJSmith Member Posts: 2,309
    edited October 2019
    atulic asks, "Won't reducing flow to these radiators affect the comfort in this room? " Yup.

    The rule is, in any circuit, the flow in one part of the circuit is the same as the flow in any other part of the circuit.

    The way your after diagram shows is that you have two circuits tied together, the toe kick circuit and the sunroom circuit. These two circuits are in parallel, not in series. As I have said, toe kick heaters are always in parallel on a series circuit, otherwise you wouldn't need a monoflo tee. Your diagram shows that the toe kick isn't connected to a series circuit with the sunroom.

    Without balancing valves the flow in each circuit would be different.
    The least restrictive circuit getting the greatest flow.

    The pressure loss thru a baseboard is a lot less than the pressure loss thru a toe kick at a given flow . The reason being is that the baseboard is a straight 3/4" and the toe kick is 1/2" in a serpentine configuration. Which is why, one doesn't connect a baseboard directly to a toe kick. You are throttling the flow in the whole circuit that way. Less flow, less BTUs to the up & downstream baseboards.

    I wouldn't pipe the way your after diagram shows, but that's me.
    Would your after diagram work, probably, but would you be happy with the results?

    Look, any radiator is going to extract BTUs from a heated flow. (As long as there is a temperature differential between the environment and the heated flow. I had to add that for the theorists out there.) The only difference between baseboard and a toe kick is that a toe kick does it in a smaller footprint. You are always going to steal heat energy from the sunroom unless the toe kick is connected to the output of the sunroom.

    Whether one uses one or two monoflo tees depend on the need to over come the pressure loss in the toe kick circuit. A toe kick that is far away from the supply pipe (3/4"), connected with 1/2" pipe may need two monoflo tees to overcome the pressure loss in the extended 1/2" supply & return piping to the toe kick. One would want to keep the 1/2" supply pipe to the toe kick as short as possible.