Column radiator question

mordzy · 26 Oct 2020

Hello, I have a few modern column rads in my house and find they take ages to warm up and don’t get particularly hot.

my house is 200 years old and is a cold house anyway, the CH pipe work is mostly 15mm which I know won’t help. I had a new 40kw ideal boiler installed last year which did improve things over the previous.

my question or rather musing is is around the column rads, while they are rated correctly BTU wise, I’m presuming they hold lots more water, as such are they relativity inefficient compared to a normal rad? My thought is the more water in the system the longer it takes to heat up and also requires more energy?

can someone clarify this or is it negligible.

With the cold nights coming I thought I might change them.

thanks

denso13 · 26 Oct 2020

mordzy said:
can someone clarify this or is it negligible.

All correct and on 15mm that could be a problem. Are they new and have they ever worked properly?

oldbuffer · 26 Oct 2020

1. It might take longer to heat up a large mass of water, but it will also take longer to cool down, so the net effect on efficiency is broadly zero.
2. Might be worth checking each radiator individually to see if all have the same problem. Many column radiators require the flow into and return from the radiator to be correctly connected to the flow and return pipes of the heating system respectively.
3. Do the non-vertical radiators become normally hot?
4. What temperature do you have your central heating water set to at the boiler? (assuming its variable).

mordzy · 26 Oct 2020

Yeh I know the 15 mm could be an issue but there’s on 4 rads (column types) + two towel rads (which get spanking hot)

I understand the flow being connected on the correct side where the baffle is to force the hot water up the rad.

boiler is variable which is tweaked down to 65 degrees on the CH as was told having it on the maximum was also inefficient.

I get the point about longer to heat but longer to cool net effect zero but was wondering if the less mass to heat would actually allow the rad to get hot

Madrab · 27 Oct 2020

Column radiators work different that conventional convection radiators.

They work 50/50 convection/radiation whereas standard radiator work 90/10 convection/radiation and the latter are much more efficient when space heating.

With large column radiators the more efficient way to heat the room is to have them on lower for longer.

I come across this a lot in the old high ceiling'd tenements in Glasgow. People like the look of the columns but when they put them in they then find they don't heat the room as well and take a lot longer to warm the space.

Did a job in the West End recently where they had a high domed/vaulted ceiling in their living room and the customer was adamant they wanted columns, I ended up having to install 4 large 12 column rads to warm the room properly where 2 large K2 rads had done the job previously.

It's the old adage of form over function.

15mm F&R and supply pipes will always struggle with large rads.

mordzy · 2 Nov 2020

I think when I originally looked at them and have since checked, the BTU of the column ones I have are 3 times higher than the equivalent 'central heating rads' dimensions are 1500x600 and are rated at 6000+btu at 50 degrees. The normal white central heating ones are around 2000btu at the same size, so I guess I was sold on the numbers?

So you're saying the columns are better at heating a room at a lower temp over a longer period? where in a normal house you actually want it to heat up quickly and then turn off so the boiler isn't running all the time?

Everything ive read seems to contradict what you are saying. In that columns have a larger surface area than a panel one so are more efficient at heating a room and are more suited to rooms with high ceilings because of this.

For ref, the room I'm talking about is standard height 5m x 5m the coldest room in the house with a 6000btu radiator.

Madrab · 2 Nov 2020

Depends .... your nice new condensing boiler will condense much more efficiently at lower temps and as long as it is happy modulating down then it'll be quite happy ticking along but if you want quicker room heat up times then the convection types are much faster at heating the space.

The column rad will tend to have a higher BTU rating as it's surface area is larger, it just heats the air in a different way than a convection rad does. It also depends on the size/ceiling height of the rooms too of course as to how the room pysically warms up.

Where are you getting your figures from? - A typical 1500mm x 600mm K2 rad is over 9500 BTU.

ScottishGasMan · 2 Nov 2020

Think you might be getting some figures mixed up to begin with, best sticking to watts as thats been the industry standard for many years. And bear in mind the output often is not at 50 degrees flow temp but at 50 degree mean water/air temp, which means you need to take 50 degrees off the average water temp, ie 80 degree flow, 60 degree return averages 70 degrees, minus 50 gives 20 degrees (20 degree room temp) so your not getting (X)Kw at 50 degree flow temp, its that output when the mean water temp is 50 degrees above the room setpoint.

If efficiency is what your after then columbs arent likley the right choice unless there a decent size in a small heat loss area, Good large convector rads sized to a flow temperature of not more than 55 degrees would be much more efficient, but you have to work within your limits space and pipework wise to get the best bang for buck you can

mordzy · 3 Nov 2020

Columnrads.co.UK for the ones I have,

I looked at Victoria plumb etc for some normal rads but the info could be wrong. Sounds like it might be definitely worth trying a different rad at that rating.

ceiling is 2400 approx.

actually not that fussed for efficiency, I just want the room to get warm in a relatively reasonable time without running the boiler for a long time before it get warm. My original question re the water volume still makes me think this is why it takes a long time to get hot.

im going to experiment a bit this weekend, shut off all other rads and see how long this one takes to heat, and how hot it gets relative to boiler temp.

work backwards from that. If it’s pretty proor just on one rad, I think I have other issues perhaps. Though if the flow needs to be hotter also (currently set to 65 at the boiler) is this counter to what you said in terms of the watt rating calculation? Do I need to up the boiler temp?

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Column radiator question

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