Why a heating system should never be guessed
The most common method in Algeria is to count the rooms, multiply by a number picked up on site, and order a boiler with plenty of margin. That margin costs money twice: once at purchase, and then every winter afterwards.
An oversized boiler reaches its setpoint too quickly, shuts down, fires again, and repeats. Those short cycles wear the ignition and the heat exchanger, ruin real-world efficiency and create uncomfortable temperature swings. An undersized boiler, on the other hand, runs continuously and never warms the far bedroom. Correct sizing is not engineering refinement: it is the difference between a system that lasts and one that gets replaced.
The heat load calculation, room by room
The principle is simple: a room loses heat through its surfaces and through the air that changes. Heating must exactly compensate those losses at the worst design outdoor temperature for the site. Algiers has a mild winter, but a humid and windy one, which changes the picture compared with an inland city — humidity and wind exposure weigh as much as the thermometer.
What actually gets measured
- Heat-losing surfaces: external walls, roof or terrace, floors over a crawl space or a garage. A corner room under a terrace loses far more than a room in the middle of the block.
- Glazing: the weak point. Single glazing lets through several times more heat than the same area of wall. Glazed area and orientation weigh heavily on the result.
- Wall build-up: single hollow brick, double leaf with cavity, insulation present or absent. This is not a detail, it is the dominant factor.
- Air change: infiltration through the windows plus the ventilation the room needs. A tight new home loses far less here than an old one.
- Room use: a bathroom, a bedroom and a living room are not heated to the same setpoint.
It stops you buying a bigger boiler than you need, which is a direct saving at purchase.
It gives every room the radiator that matches it, so the house heats evenly instead of having a stifling lounge and a cold bedroom.
It produces the flow rates, hence the pipe sizes, hence a silent system.
Choosing the boiler
Boiler output follows from the sum of the heat losses, plus the domestic hot water demand if the appliance is a combi. Routinely adding a third for peace of mind has no technical basis.
The second choice is the appliance type. A room-sealed boiler, drawing its combustion air from outside and discharging outside, is safer than a natural-draught appliance taking air from the room: it removes the risk tied to air starvation and flue spillage. On efficiency, a condensing boiler only delivers its advantage if it runs with a fairly cool return temperature, which requires correctly sized radiators — and so, once again, the heat load calculation.
Emitters: radiators and surfaces
A radiator is defined by its output in watts, not by its length, and that output is quoted for a specific temperature difference between water and air. The same radiator fed at 70 °C does not deliver what it delivers at 50 °C. That is why any catalogue always states the test conditions.
- Steel: quick to react, moderate price, the domestic standard.
- Aluminium: very responsive and light, but sensitive to the quality of the circuit water.
- Cast iron: heavy and slow, yet it keeps giving heat back — worth considering in a large, continuously occupied room.
- Underfloor heating: better comfort and the low temperature a condensing boiler loves, but it is decided at structural stage, not afterwards.
Position matters as much as size. A radiator under a window counters the coldest zone of the room and prevents the cold-surface sensation. Hiding it behind a casing or furniture cancels a significant part of its output.
The pipework: where fluid mechanics comes in
Once the outputs are known, the required water flow rates follow, and from those flow rates come the pipe diameters. The logic is the same as for drinking water: too small a bore raises velocity, which produces noise and friction losses the pump must overcome by drawing more power.
Three possible layouts
| Layout | Principle | When to use it |
|---|---|---|
| One-pipe | Radiators connected in series on a single loop | Cheap in pipework, but the last radiators receive water that has already cooled. Avoid in a villa. |
| Two-pipe | A common flow and return, each radiator on a branch | The reference solution: every emitter receives the same flow temperature. |
| Manifold | A central manifold, one continuous pair of pipes per radiator | No buried joints in the slab, easy individual adjustment. Ideal in new build, using multilayer or PEX. |
Sizing keeps circulation velocity moderate — on the order of 0.3 to 1 m/s in domestic pipework. Below that, air no longer gets pushed out. Above it, the circuit whistles and the pump struggles.
In new build, prefer continuous runs with no joint buried in the slab: whatever is encased must be unbroken.
Balancing: why the far bedroom stays cold
Water, like electricity, takes the easiest path. With no adjustment, the radiator nearest the boiler takes most of the flow and the furthest one gets a trickle. The usual reflex — turning the boiler temperature up — overheats the lounge and changes nothing in the back bedroom.
The answer is to set the regulating valves or lockshields: you deliberately restrict the short circuits to force water to travel to the end. It is a commissioning task that needs method, not extra hardware. A new installation handed over without balancing is only half handed over.
Domestic hot water: the recirculation loop
In a villa, the furthest bathroom can be fifteen metres from where hot water is produced. Every shower then starts by running several litres of cold water down the drain, and the wait repeats several times a day.
A recirculation loop solves it: a small pump keeps hot water moving through a return pipe, so hot water is available almost instantly at the tap. Two conditions make it worthwhile: the pipe must be insulated along its whole route, and the pump must be controlled by a timer or thermostat — otherwise you save water by burning gas.
Safety and control: the parts people forget to price
- The expansion vessel: heated water expands. An undersized or deflated vessel drives pressure up and makes the relief valve drip every time the boiler fires. It is the most common cause of mysterious pressure loss.
- The safety relief valve: it protects the circuit against overpressure and must discharge somewhere visible, not into a wall.
- Air vents: at the top of every riser and on every radiator, otherwise air collects where it cannot be released.
- Separation from drinking water: the filling connection must never stay permanently joined to the main without a protective device.
- Controls: a well-placed room thermostat, plus thermostatic valves on secondary rooms, buy more comfort than a few extra kilowatts of boiler.
Frequently asked questions
How long does a heating study take for a villa?
Half a day to a day for a typical two-storey villa, survey and room-by-room calculation included. The output is a table of outputs per room, the boiler size, the radiator schedule and the pipework layout.
Does underfloor heating suit the Algiers climate?
Yes, and it works particularly well with a condensing boiler thanks to its low operating temperature. The constraint is not climate but timing: it has to be decided before the slab. Afterwards you need an added screed, which is not always feasible.
Should thermostatic valves go everywhere?
No. Avoid them in the room where the room thermostat sits, otherwise the two controls fight each other. Elsewhere they are useful for turning down unoccupied bedrooms and circulation spaces.
Steel or aluminium radiators?
Both are sound. Aluminium heats faster and weighs less; steel is more tolerant of poor circuit water. The choice mostly comes down to water quality and budget, not to any inherent superiority.
Which parts of Algiers do you cover for new builds?
The whole wilaya: villas in Hydra, El Biar, Dely Ibrahim, Ouled Fayet and Chéraga, new residences in Zéralda and Sidi Abdellah, apartment blocks in Bab Ezzouar and Bordj El Kiffan.
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About the author
University training in process engineering (industrial chemistry and process engineering, University of Jijel). Working since 2018 in plumbing, central heating and air conditioning under the El Itqan name. Studies the Toronto plumbing programme (Ontario, Canada) and works to the International Plumbing Code (IPC). The guides on this site are written from real jobs, not from product sheets.
Ask a question about your installation →This guide is general information. It does not replace an on-site diagnosis by a professional, and no work on a gas installation should ever be attempted by a non-professional.