Mixing unit for underfloor heating

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Today, among the heat­ing sys­tems used in every­day life, warm water floors are gain­ing pop­u­lar­i­ty. Increased atten­tion on the part of con­sumers to this method of heat­ing is due to the high effi­cien­cy of heat­ing floors, espe­cial­ly when the empha­sis is on the qual­i­ty of inte­ri­or dec­o­ra­tion of res­i­den­tial premis­es. Heat­ing radi­a­tors do not always look aes­thet­i­cal­ly pleas­ing, while the water cir­cuit hid­den in the floor is com­plete­ly invis­i­ble.

In this case, the instal­la­tion of heat­ing equip­ment also bribes. With prop­er plan­ning and obser­vance of all the nec­es­sary tech­no­log­i­cal sub­tleties, mak­ing under­floor heat­ing in your own home is quite real­is­tic and with­in the pow­er of every­one. In order to suc­ceed, it is enough to have an idea of ​​​​how the under­floor heat­ing works, which is includ­ed in the equip­ment. In the process of work, you will have to face not only the choice of the method of heat­ing the coolant, the selec­tion and lay­ing of water cir­cuit pipes and screed equip­ment. The key ele­ment of the “warm water floor” heat­ing sys­tem is the under­floor heat­ing mix­ing unit.

What is this equip­ment? What is its design and pur­pose? Let’s deal with these issues in more detail.

Why do you need a mixing unit for a underfloor heating system

Under­floor heat­ing today can be found in almost any res­i­den­tial area. City apart­ments, if the design fea­tures of a res­i­den­tial facil­i­ty allow, are often heat­ed in this way. In many pri­vate hous­es, in cot­tages, water floors are a com­mon phe­nom­e­non. Due to the design fea­tures, the under­floor heat­ing sys­tem can be used both as a full-fledged, main heat­ing of res­i­den­tial premis­es, and as an aux­il­iary heat­ing option. Com­pe­tent instal­la­tion, the avail­abil­i­ty of appro­pri­ate equip­ment will allow you to use water floors with max­i­mum effi­cien­cy. And it will help you with this, a mix­ing unit for your warm floors.

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Warm water floors is a low-tem­per­a­ture heat­ing sys­tem. Unlike radi­a­tors, for the nor­mal oper­a­tion of heat­ing water cir­cuits, it is nec­es­sary to have a coolant whose tem­per­a­ture varies between 35–550C. The water that cir­cu­lates in the cen­tral heat­ing sys­tem is much hot­ter, not to men­tion the heat car­ri­er heat­ed as a result of the oper­a­tion of the heat­ing boil­er. The work of prepar­ing water for water cir­cuits is per­formed by a mix­ing unit. On top of that, through the sys­tem of col­lec­tor inputs, the dis­tri­b­u­tion of the coolant through the under­floor heat­ing pipeline is car­ried out.

On a note: it should be said that a mix­ing unit or a mix­ing unit is nec­es­sary when you have expressed a desire to make heat­ing in your house through under­floor heat­ing. For oth­er heat­ing options, this tech­nique is not required.

The principle of operation of the mixing unit

Like all oth­er heat­ing sys­tems that use a liq­uid coolant, heat­ing due to water-heat­ed floors works in a sim­i­lar way:

  • heat­ing source (autonomous boil­er or cen­tral heat­ing ris­er);
  • sup­ply and return pipelines, water cir­cuits laid in the floor of a heat­ed room;
  • devices and instru­ments of the reg­u­la­to­ry group.

Water is heat­ed by the oper­a­tion of the boil­er or sup­plied to the sys­tem from the DHW line and cen­tral heat­ing. In an autonomous boil­er, water is heat­ed to a tem­per­a­ture of 75–950C, in the CH sys­tem the water tem­per­a­ture is slight­ly low­er, 55–750C. In accor­dance with health reg­u­la­tions, the ide­al floor heat­ing tem­per­a­ture should be 310C, thanks to which a zone of com­fort­able stay is cre­at­ed in a heat­ed room. In order to achieve such tem­per­a­ture para­me­ters, water heat­ed to a tem­per­a­ture of 35–550C. The puff cake absorbs excess ther­mal ener­gy, giv­ing out opti­mal tem­per­a­ture indi­ca­tors on the floor sur­face.

In order to direct the flow of water of the required tem­per­a­ture into the water cir­cuit, a mix­ing unit for a warm floor is installed. Oth­er­wise, the under­floor heat­ing sys­tem will be a waste of mon­ey. With­out adjust­ing the tem­per­a­ture of the coolant, your floor will turn into a hot pan, and the con­crete screed and floor cov­er­ing will soon become unus­able.

Impor­tant! It should be remem­bered that the mix­ing unit can only work if ordi­nary water cir­cu­lates in the heat­ing sys­tem.

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The unit is mount­ed in the imme­di­ate vicin­i­ty of the heat­ed room, where the heat­ing cir­cuit loops come to the sur­face. The equip­ment is con­nect­ed to both pipes, to the hot water sup­ply pipeline and to the return flow line. As a result of its work, the exces­sive­ly hot coolant mix­es with the cooled down, cooled down waste water, result­ing in the opti­mum water tem­per­a­ture for the heat­ing pipes.

Impor­tant! If the water in the sys­tem is not so crit­i­cal for under­floor heat­ing, it is not nec­es­sary to install a mix­ing unit. If an autonomous boil­er works for heat­ing and pro­vides hot water for domes­tic pur­pos­es, you can­not do with­out a mix­ing unit.

It would be appro­pri­ate to say. Do not con­fuse the mix­ing unit and the man­i­fold. The first is a set of equip­ment, each of which indi­vid­u­al­ly per­forms the func­tions assigned to it. The col­lec­tor is an inte­gral part of the mix­ing unit and is designed to col­lect and dis­trib­ute water flows in the heat­ing sys­tem.

Based on the con­fig­u­ra­tion, the prin­ci­ple of oper­a­tion of the mix­ing unit fol­lows.

The heat car­ri­er from the heat­ing source enters the col­lec­tor. The pres­ence of a safe­ty valve and a ther­mo­stat does not allow hot water to move freely fur­ther. At a high water tem­per­a­ture, the auto­mat­ic mode is acti­vat­ed. The inlet valve opens and cold water is added to the hot flu­id flow, flow­ing in the oppo­site direc­tion. When the water reach­es the required tem­per­a­ture val­ues, the valve auto­mat­i­cal­ly clos­es, stop­ping the sup­ply of hot water to the sys­tem. This process occurs con­stant­ly and unin­ter­rupt­ed­ly dur­ing the oper­a­tion of the heat­ing sys­tem.

Mixing unit completeness

The prin­ci­ple of oper­a­tion of the equip­ment is sim­ple and clear. Anoth­er thing is what devices and equip­ment pro­vides the func­tion­al­i­ty of the entire unit. The eas­i­est option that you can do your­self is a mix­er equipped with a man­i­fold, a safe­ty valve and a cir­cu­la­tion pump.

The first per­forms the task of dis­trib­ut­ing the flow through the water pipes of the under­floor heat­ing. The safe­ty valve pro­vides hot water sup­ply to the col­lec­tor and con­trol of the water heat­ing tem­per­a­ture.

The cir­cu­la­tion pump com­mu­ni­cates the required speed to the water flow, ensur­ing the inten­si­ty and uni­for­mi­ty of water sup­ply to the under­floor heat­ing sys­tem.

A more com­plex mix­er design is a whole set of addi­tion­al ele­ments. In addi­tion to the devices already men­tioned, a man­i­fold, a safe­ty valve and a sup­ply pump, the kit of a con­ven­tion­al mix­ing unit includes:

  • Bypass — an ele­ment that pro­tects your equip­ment from over­load and over­heat­ing;
  • Drain, bleed valve;
  • Shut-off valve;
  • Air vents;
  • Ther­mal relay.

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The mix­ing unit should be a com­pact design that can be suc­cess­ful­ly hid­den in a man­i­fold cab­i­net.

On a note: if it is planned to equip under­floor heat­ing in sev­er­al rooms, each of them will require its own sep­a­rate mix­ing unit. You can install one sin­gle unit for all heat­ing cir­cuits, only in this case it is bet­ter to use a col­lec­tor with a large num­ber of inputs and an addi­tion­al amount of safe­ty fit­tings.

Mix­ers are usu­al­ly equipped with three-way and two-way valves. The sec­ond is also called the sup­ply valve. Thanks to its fill­ing, ther­mo­stat and sen­sor, the valve reacts to the slight­est change in the tem­per­a­ture of water heat­ing in the sys­tem, open­ing or shut­ting off the water sup­ply.

For heat­ed rooms with an area of ​​more than 200 m2 the use of a two-way valve is not rec­om­mend­ed.


The three-way valve has sev­er­al func­tions. Due to its design, the valve is capa­ble of divert­ing and mix­ing. Thanks to such a device in the mix­ing unit, the hot water com­ing from the heat­ing device is mixed with the return. Usu­al­ly, valves with ser­vo dri­ves are placed on the mix­ture, which inde­pen­dent­ly, in auto­mat­ic mode, reg­u­late the lev­el of mix­ture. Com­ple­ment­ing the mix­ing block with a three-way valve com­plete with a weath­er-depen­dent con­troller, you will receive a ful­ly auto­mat­ed heat­ing tem­per­a­ture con­trol sys­tem. In addi­tion, the three-way valve is designed to work with warm floors of a large area.

If you want to save on equip­ment, use man­u­al adjust­ment valves. By sav­ing on automa­tion, you will get extra has­sle for your­self. With man­u­al adjust­ment, it is quite dif­fi­cult to deter­mine the opti­mal flow of the coolant in the sys­tem. Automa­tion solves these issues eas­i­er and faster.

Installation of the mixing unit. Installation Features

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With the right selec­tion of com­po­nents, sub­ject to all the nec­es­sary tech­ni­cal con­di­tions, the instal­la­tion of the mix­er should not cause dif­fi­cul­ties. Hav­ing deter­mined the loca­tion of the mix­ing unit, hav­ing sim­u­lat­ed the design of the man­i­fold cab­i­net, start the assem­bly.

For the future. The under­floor heat­ing con­trol unit must have free access. Oth­er­wise, you will have to face dif­fi­cul­ties dur­ing oper­a­tion.

First, the pipelines com­ing from the heater are con­nect­ed. The col­lec­tor is installed next. At the end, the sys­tem can be equipped with sen­sors for adjust­ing pres­sure, pres­sure and ther­mome­ters. It is impor­tant to deter­mine the way the col­lec­tor combs are locat­ed. The type of heat­ing source your sys­tem is con­nect­ed to deter­mines how the dis­tri­b­u­tion man­i­folds are con­nect­ed. It can be an end con­nec­tion or a reg­u­lar one, top and bot­tom.

For the hot water sup­ply line, it is bet­ter to use met­al-plas­tic pipes or poly­mer­ic mate­ri­als. These com­po­nents are able to cope with pres­sure surges in the sys­tem, and per­fect­ly with­stand high tem­per­a­tures.


Con­nec­tion of equip­ment to water cir­cuits is car­ried out in a clear sequence using fit­tings. Pipes are con­nect­ed to the blue inlet pipes, through which the cooled water flows in the oppo­site direc­tion. A water loop is con­nect­ed to the red pipes, which pro­vides floor heat­ing in a heat­ed room.

If you are plan­ning to make a warm floor for heat­ing large areas, you will def­i­nite­ly need a cir­cu­la­tion pump. The large length of the water cir­cuit, the large num­ber of bends and the small diam­e­ter of the heat­ing pipe lead to the fact that the cir­cu­la­tion of the coolant in the sys­tem notice­ably weak­ens. By installing a cir­cu­la­tion pump, you will ensure the nor­mal sup­ply of pre­pared water to the heat­ing cir­cuits. It is rec­om­mend­ed to install the pump at the begin­ning of the mix­ing unit, where the sup­ply pipe is suit­able and the return is con­nect­ed.

The pump is installed in a strict­ly hor­i­zon­tal posi­tion. It is rec­om­mend­ed to install pumps with sev­er­al speed modes. These mod­els allow you to man­u­al­ly deter­mine the required feed rate and flow rate.

In custody

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Hav­ing become acquaint­ed with the impor­tance of the mix­ing unit for the “warm water floors” heat­ing sys­tem, how its work is arranged, we can say a few words about set­ting up the equip­ment. With­out prop­er train­ing, it is bet­ter to entrust such a pro­ce­dure to spe­cial­ists — heat engi­neers. Despite the fact that the instal­la­tion of a warm floor and the instal­la­tion of a mix­er are tasks that you can han­dle on your own, set­ting up a reg­u­lat­ing group requires appro­pri­ate qual­i­fi­ca­tions and knowl­edge.

For gen­er­al infor­ma­tion, we note a cou­ple of steps that are asso­ci­at­ed with the process of set­ting up the mix­er.

  • It is bet­ter to remove ther­mal heads or valves with ser­vo dri­ves so that they do not affect the set­ting of the mix­ing unit;
  • The bypass valve is set to a max­i­mum val­ue of ‑0.6 atm, mak­ing it cur­rent­ly inop­er­a­tive;
  • The posi­tion of the bal­anc­ing valve is set accord­ing to the capac­i­ty cal­cu­la­tions;

The cal­cu­la­tions will be some­thing like this:

Where, t1 is the tem­per­a­ture of the water in the sup­ply pipe from an autonomous boil­er or CH sys­tem;

t2supply is the water tem­per­a­ture at the inlet to the water cir­cuit;

t2return is the return water tem­per­a­ture com­ing from the water cir­cuit loop;

Kvt is a gen­er­al­ly accept­ed coef­fi­cient, which is equal to the val­ue of 0.9.

We take the aver­age num­bers for cal­cu­la­tions, for the oper­a­tion of an autonomous boil­er:

t1=95 °С,

t2 sup­ply = 45 °С,

t2arr = 35 °С.

As a result, we get:

This is the val­ue that we set on the bal­anc­ing valve.

Next, we set up the pump, tak­ing into account the capac­i­ty of the bal­anc­ing valve and the required inten­si­ty of water flow. If you can­not con­fig­ure the pump tak­ing into account the opti­mal para­me­ters, set the min­i­mum oper­at­ing modes on it. In the future, when it becomes clear that the oper­at­ing speed of the pump is not enough, reset the unit to a high­er speed.

  • The last stage is con­nect­ed with bal­anc­ing the water floor loop. Bal­anc­ing valves cope with this task. If you have one branch of the heat­ing cir­cuit, bal­anc­ing is not required.

In con­clu­sion, it should be said that the assem­bled mix­ing unit and con­nect­ed to the sys­tem requires manda­to­ry tying with the entire heat­ing sys­tem. By fol­low­ing all the nec­es­sary instruc­tions and rec­om­men­da­tions of spe­cial­ists, entrust­ing the per­for­mance of hydraulic and ther­mal cal­cu­la­tions to spe­cial­ists, you can count on a suc­cess­ful out­come of your event. A mix­ing unit, assem­bled in accor­dance with all the rules, will allow your home heat­ing sys­tem to work as effi­cient­ly as pos­si­ble. In addi­tion, you will sig­nif­i­cant­ly increase the lev­el of com­fort in the house and your own safe­ty.

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