Improving central heating
 

Like many people we have gas central heating. What I often wonder about is trying to make it work better. What I am thinking about is how the heat fills the room. So the heating comes on, the temperature in the radiator rises and cold air at the bottom rises through it and continues on rising towards the ceiling. This continues until the air at the level of the thermostat has reached it's setpoint and it turns the heating off. This means the air above it is hotter than the setpoint and that below it is colder.

I did think that a ceiling fan might help but the air it pushes down wont go far unless the fan is quite powerful. So what I'm wondering is would it work better if there is a fan below the bottom of the radiator blowing the cold floor level air up through it. This would warm a greater amount of air per minute but it would be cooler and the fan would be constantly dragging the colder air down thus evening out the temperature from ceiling to floor.
Does that sound practical or can you see some error in my reasoning?

I once started a discussion about increasing the efficiency of my heating system by lowering its temperature:
How to lower heating system temperature?

There Ryland proposed installing fans under the radiators, mostly to increase the heat transfer (more heat to the room, with the extra benefit of lowering the temperature of the water returning to the boiler for additional efficiency). These would also slightly boost air circulation, as you mentioned.

Since then I have had 120mm computer fans under most of the radiators in the house. Do they help? Yes, but not enough to measure. Mostly because the effect of the low flow from the fans on the massive, cast iron radiators is a tiny percent of all of the energy.
The effect on lighter, thin radiators would be much more noticeable, especially with higher effeciency fans, blowing air across the full length of the radiator, not just a 120mm segment of it.

Thanks Piwoslaw. it's as I thought. We do have the thin radiators. Because the air nearer the ceiling will be the hottest in the room then that's where the greatest Δt will be causing more heat loss than with what I hoped would improve the overall efficiency.
I did think it would be better to have the airflow increased across the whole of the radiator.
I have been wondering how I could do it without using a lot of power to produce it. I guess there has to be a sweet spot but exactly what that would be is probably something I would have to do empirically. I might get a few smaller PC fans and arrange them in a row along the bottom rather than a bigger fan with ducting. I can get 4 of the 60mm fans from Amazon at GBP9 and they are 5V 0.1amp each with air flow of 13.8CFM

If I were to invest more into this idea, I would experiment with a squirrel cage fan, but with a looong fan, like this:
https://ecorenovator.org/forum/attac...8&d=1702387800
This would give an even flow over a longer length.

If you do go with the PC fans, take the largest diameter you can. Take the next largest and mount it diagonally to make it fit. The reason is noise - the smaller the fan, the higher the rpms and the worse the noise.
I had to put a resistor on 1 or 2 of mine to make them acceptable by the family.

The ones I mentioned say Noise:26dBA. And some 30mm ones say 15.92dBA which I can get 6 for GBP10. No idea what airflow they produce as it's not stated. Bigger fans would need to be tilted quite a lot as the radiators are quite narrow. The double ones are only 72mm wide so if I got bigger fans I would need to add some sort of ducting to route the air. The squirrel cage one looked like a possibility but I've not found anything suitable here so far. They all seem to be large diameter and short and are 240 volts except for 1 which was a replacement for a fireplace and had a built in heater so was not cased as it was for fitting internally.

Along these lines I thought of a central duct with a fan pushing cooler basement air up and another fan pushing warm attic air down. (adding to heat or cool the main floor)
Then I though about a reversable fan/blower instead, but all the sensors to make it automated made me crazy....
I still think its an idea worth trying but I don't have the means to implement it (so far)