How to drain water from a warm floor?


Instal­la­tion of a warm floor involves the sub­se­quent long-term and unin­ter­rupt­ed oper­a­tion of the heat­ing sys­tem. In a city apart­ment, a pri­vate house or a coun­try house, a water-heat­ed floor is equal­ly effec­tive and con­ve­nient. Such a heat­ing sys­tem can be equipped in almost any res­i­den­tial area, but the effec­tive­ness of its use depends on the com­pli­ance of the tech­ni­cal char­ac­ter­is­tics of the equip­ment with the design fea­tures of the room. Prop­er­ly cal­cu­lat­ed and installed heat­ing cir­cuits, expert­ly per­formed pres­sure test­ing of the under­floor heat­ing sys­tem will allow home­own­ers to for­get about the has­sle of main­tain­ing heat­ing devices for a long time.

The pro­ce­dure for press­ing the heat­ing cir­cuit of warm water floors

How­ev­er, the idyll can­not con­tin­ue indef­i­nite­ly — any equip­ment is not eter­nal and even­tu­al­ly needs to be repaired. Under­floor heat­ing is a com­plex com­plex of a wide vari­ety of equip­ment, the fail­ure of one of the ele­ments of which can lead to the fail­ure of the entire heat­ing sys­tem.

In some cas­es, for exam­ple, in case of prob­lems with the through­put or tight­ness of the floor water heat­ing pipeline, the preser­va­tion of hous­ing has to be drained from the heat­ing cir­cuit.

Let us con­sid­er in more detail in which cas­es it is nec­es­sary to drain the liq­uid from the under­floor heat­ing sys­tem, and how this is done.

The main reasons for draining water from the underfloor heating system

There can be quite a few rea­sons why it becomes nec­es­sary to drain the water from the pipeline of the heat­ing sys­tem your­self — from the upcom­ing long absence of res­i­dents in the house to replac­ing the water in the sys­tem with antifreeze. In order to do every­thing right, and not dam­age the heat­ing sys­tem, let’s take a clos­er look at how to drain water from the warm floor on your own.

A com­mon rea­son for the need to drain the coolant is the con­ser­va­tion of the heat­ing sys­tem for the win­ter when used in a nor­mal water cir­cuit. This event, before the onset of cold weath­er, is main­ly car­ried out in sum­mer cot­tages and coun­try hous­es that are not used in win­ter. To sim­pli­fy and speed up the drain­ing process, spe­cial equip­ment is used.

Portable Air Com­pres­sors (Motor Dri­ven)

Impor­tant! In hous­ing for sea­son­al use, fail­ure to drain the water from the under­floor heat­ing cir­cuit before the onset of frost is fraught with defrost­ing of the sys­tem, there­fore, the use of antifreezes as a coolant is undoubt­ed­ly prefer­able — in addi­tion to resis­tance to low tem­per­a­tures, these liq­uids are less sub­ject to wear pump parts.

Anoth­er equal­ly impor­tant mea­sure in the oper­a­tion of under­floor heat­ing is pre­ven­tive main­te­nance on the heat­ing sys­tem. Boil­er water has a lot of impu­ri­ties that, when heat­ed, pre­cip­i­tate or form lay­ers on the walls of the pipeline. Due to the decrease in the inter­nal clear­ance of the heat con­duc­tors, the cir­cu­la­tion of the coolant in the sys­tem is dis­turbed, and heat trans­fer is reduced. For this rea­son, when using water, the coolant must be drained once or twice a year.

A water cir­cuit filled with antifreeze does not suf­fer from such a prob­lem. The replace­ment of the coolant in this case is car­ried out every 3–5 years — pro­vid­ed that the boil­er is oper­at­ed with­out over­heat­ing (for warm floors, the max­i­mum allow­able tem­per­a­ture thresh­old for heat­ing the coolant is 45–550FROM).

One of the types of antifreeze for fill­ing the con­tours of the under­floor heat­ing sys­tem


Anoth­er rea­son for the need to drain the coolant may be the loss of its phys­i­cal prop­er­ties by the liq­uid. The change in the char­ac­ter­is­tics of antifreeze occurs after over­heat­ing — the solu­tion begins to foam, fill­ing cer­tain sec­tions of the heat pipes with foam, which dis­rupts the cir­cu­la­tion of the coolant in the sys­tem and reduces heat trans­fer.

Fail­ure to com­ply with the instal­la­tion tech­nol­o­gy of a warm floor, the use of mate­ri­als that are not intend­ed for con­tact with chem­i­cals, caus­es the occur­rence of cor­ro­sive process­es in the heat­ing sys­tem, as a result of which the cir­cu­la­tion of the coolant is also dis­turbed, and water cir­cuit leaks occur.

Nat­u­ral­ly, you will have to drain the water from the under­floor heat­ing pipeline when replac­ing it with antifreeze — mod­ern­iza­tion.

These are the main rea­sons for the need to emp­ty the under­floor heat­ing sys­tem and, regard­less of the basis, the water must be drained in accor­dance with all the rules, with the imple­men­ta­tion of safe­ty pre­cau­tions and com­pli­ance with the tech­no­log­i­cal sequence of the con­stituent oper­a­tions.

Procedure for draining water from the system

Under­floor heat­ing is a closed sys­tem, so you need to take care of the drain taps even at the instal­la­tion stage. The num­ber of valves must match the num­ber of water cir­cuits.

Under­floor heat­ing is actu­al­ly a long hose laid in the floor. Lay­ing method — the con­fig­u­ra­tion of the con­tours may be dif­fer­ent, but the prin­ci­ple of oper­a­tion of the water cir­cuit is the same — the coolant gives off heat to the sur­round­ing space by heat­ing the floor sur­face.

Image of the con­tour of the under­floor heat­ing sys­tem from a cop­per pipe, laid on a rein­forc­ing mesh in front of the screed device

Before start­ing the oper­a­tion to drain the coolant, the heat­ing sys­tem is turned off, after which the time required for the com­plete cool­ing of all its ele­ments is wait­ed.

Giv­en the fact that the water cir­cuit is con­nect­ed to the main pipeline, and the con­nec­tion point is locat­ed above the floor lev­el, the water is drained forcibly using an air com­pres­sor.

Note: the pow­er of a house­hold vac­u­um clean­er is not enough to emp­ty the under­floor heat­ing sys­tem.


Impor­tant! To purge the water cir­cuit, a com­pres­sor with a work­ing pres­sure of up to 5 bar is used — the use of a more pow­er­ful unit is fraught with the destruc­tion of heat pipes.

The pres­sure gauge point­er is at 6 bar — the max­i­mum allow­able purge pres­sure of the under­floor heat­ing sys­tem has been exceed­ed!

Drainage is car­ried out through a return line equipped with a drain valve, and the com­pres­sor is con­nect­ed to the man­i­fold on the inlet pipe, so the check valve may cre­ate some inter­fer­ence when blow­ing the pipe. After con­nect­ing to the col­lec­tor, the com­pres­sor for dis­plac­ing the coolant from the cir­cuit is turned on, and the air sup­ply pres­sure is grad­u­al­ly increased — to a val­ue after which the liq­uid began to flow out at the out­let. It should be remem­bered that the vol­ume of water in each of the under­floor heat­ing cir­cuits is insignif­i­cant, there­fore, an ordi­nary buck­et with a vol­ume of 8–10 liters is suf­fi­cient to receive it.

The com­pres­sor should work until air begins to flow con­tin­u­ous­ly from the pipe fol­low­ing the water.

On a note: if you don’t have a com­pres­sor handy, there is anoth­er way to free the sys­tem from water and avoid defrost­ing the heat­ing sys­tem. A hose of suit­able diam­e­ter 1 m long with a fun­nel at the end is tight­ly put on the inlet of the heat pipe. The end with the fun­nel is raised high­er and grad­u­al­ly poured into it a liq­uid for wash­ing car win­dows — “anti-freeze” (it is bet­ter to use a bright­ly col­ored one). As the water is forced out of the return pipe, and then the tech­ni­cal flu­id is a long, but effec­tive process.

Technical subtleties and nuances


In prepa­ra­tion for drain­ing, it is nec­es­sary to study the col­lec­tor device in order to find and mark on the sup­ply and return the loca­tion of the valves marked as fol­lows:

  • serv­ing — red;
  • reverse flow — blue.
Com­pres­sor con­nec­tion dia­gram for emp­ty­ing the cir­cuits of the under­floor heat­ing sys­tem

Hav­ing con­fused the flow with the return, the drain sys­tem will not work — the check valve will block the pipeline.

If there is no receiv­ing con­tain­er, then you can con­nect the drain hose to the return valve and stretch it to the near­est sew­er­age intake — a toi­let, sink or drain.

Col­lec­tor node of the sys­tem of warm water floors

Hav­ing fin­ished drain­ing the water from one cir­cuit, all the oth­ers are emp­tied in the same way. Dur­ing the drain­ing of some sec­tion of the sys­tem, the valves of the remain­ing cir­cuits must be closed, and at the end of each stage, the taps of the emp­ty pipelines must also be closed.

To ful­ly emp­ty the cir­cuits, the purge pro­ce­dure can be repeat­ed after an hour — when mois­ture drains from the walls of the heat pipes and accu­mu­lates in some area.


Peri­od­ic drain­ing of water from the under­floor heat­ing sys­tem is nec­es­sary. The fre­quen­cy of this oper­a­tion depends on the inten­si­ty of use of the heat­ing sys­tem and the qual­i­ty of the water. In regions with hard water, which also con­tains a lot of sus­pend­ed impu­ri­ties, it is nec­es­sary to drain the water from the heat­ing cir­cuit at least once a year.

Replac­ing the water in the heat­ing pipeline does not require finan­cial costs (except for the pos­si­ble pay­ment for rent­ing a com­pres­sor), there­fore it is bet­ter to per­form this manip­u­la­tion reg­u­lar­ly, there­by extend­ing the time for trou­ble-free oper­a­tion of the water cir­cuits.

When using antifreezes, the pro­ce­dure for drain­ing the coolant is car­ried out much less fre­quent­ly — once every 3–5 years, but with increased safe­ty mea­sures — eth­yl­ene gly­col, used for the man­u­fac­ture of non-freez­ing liq­uids, and its vapors are tox­ic sub­stances that require the use of per­son­al pro­tec­tive equip­ment (over­alls, gloves, gog­gles, ven­ti­la­tion) and room ven­ti­la­tion.


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