Hot-water radiators used in central heating systems use passive convection to distribute heat inside a room.
This is not very efficient, especially if they are mounted in the corner of the room.
For this reason, there are convector radiators that include a fan in order to improve the heat distribution and circulate higher volumes of air through the radiator blades.

In this alternative approach, standard radiators are upgraded to convector radiators using commercial off-the-shelf components (COTS) for 35€.

Step 1: Assembling the Fans

These 4 fans are Brushless DC Cooling Fan 7 Blade 24V 120mm x 120mmx25mm.
This type of fan is very silent and about the same width as the hot-water radiator. By joining 4 fans together, they cover almost the entire radiator length.

Fan characteristics:
- 7 Plastic Blades
- Speed: 1600 RPM
- Airflow: 58 CFM
- Noise: 38 DBA
- Rating: DC 24V, 0.20A

These 4 fans were bought online for a total of 13.20€, plus 10.10€ for shipping.

The structural strength is given by the cable ties that pass through the holes in the corner of each fan, and join the fans together.

Step 2: Connecting the Cables

The fans use standard 2 pin connectors found in motherboards.
These hold quite well the tip of a coper cable.
It is also possible to merge 2 connectors with a small piece of cable, by plugging one to the back of another.
This minimises the number of cables reaching the power supply.

The power supply connected with a basic 2 wires AC cable on one side, and the DC cables from the fans on the other side.

Not shown in the pictures is a 1.5€ pass-through on/off switch and a basic AC plug (1.5€) at the end of the AC cable.

The power supply is a 24V Universal Regulated Switching 25W Power Supply.
Since the fans are 0.2A each and the power supply is rated at 1.0A, there is a margin in terms of the maximum current allowed.

Step 3: Testing the Fans

Here are the fans working before installing under the radiator.

Step 4: Installing the Legs and Finishing Up

The fans were fitted with 4 legs using a plastic corner strip, cut into 15cm each.
These were then slided under the radiator.

The end result was a significant increase in heat distribution, with fans that almost silent and a system that only consumes 24W:

- fans: 4*0.2A*24V=19.2W
- power supply: rated at 80% efficiency
- total power: 19.2/80%=24W

That is how you upgrade a standard hot-water radiator to a convector radiator.

Upgrade: You can also use 2 cable ties joint together to suspend the fans from the radiator by looping around the bottom tube in the radiator. Only 2 cable ties on each end of the fans should be more than enough.

Since the maximum temperature is around 60ºC, the cable ties can more than handle the heat. This way the fans are totally suspended and almost look like part of the system. It is also easier to clean underneath with the vacuum cleaner.