Undersized Radiators - Inefficient?

retepetsir

Morning everyone

We bought our 2-bedroom 1970 flat last February and I've always thought that the radiators were too small for the size of the place (quite a spacious flat). Coming in to the colder weather and that now seems more obvious as it takes an age to heat up, and the boiler fires quite regularly.

I fitted a Honeywell DT90 digital thermstat to regulate the boiler more accurately, but having sat down yesterday to calculate the radiator sizes I think they're far too small.

We have a Potterton Profile 50e which is rated at 11.72-14.65kW. Yet I believe the total radiator output is 5.75kW, and adding 30% for hot water heating and pipe losses that brings it to only 7.5kW.

Would it therefore be more efficient to fit some larger radiators?

As an example, we're in a ground floor flat (not well insulated) and in the main bedroom the radiator is 800mm x 600mm single panel ~750W, yet the room is 3.8m x 3m in size . The recommendation based on 3 outside walls and concrete floors is at least 1600W.

It never seems to get warm in there at all, so would it be ok if I upgraded this to say a 1400mm x 600mm double panel which is more like 2700W? We do suffer with cold spots/damp/condensation.

The rest of the flat's radiators are also small (but are in smaller rooms), all single panels expect for the lounge which is a larger double panel radiator.

I think the previous occupant converted it to gas central heating on the cheap as the radiator size just doesn't seem right to me? If the boiler is rated higher and the total radiator kW is only 7.5kW with losses, that seems to me that the efficiency would be rather low?

I'm hoping to complete the work myself :eek:

Never dealt with plumbing before, usually just electrics :rotfl:

Thanks

karl-123

some gas installers say

a big radiator in a big room
a small radiator in a small room

this shows there lack of training, :mad:
i spent 4 years at college
3 years plumbing ( 603-1 and 603-2 )
1 year gas

use a mears calculator and add ten percent,

http://www.mhmear.com/index.html

ormus

a boiler should cope with a 2 bed flat quite easily, so changing to a larger radiator shoulnt be a problem.

ps
the efficiency of a boiler is how well it converts the gas (the energy) into heat.
modern condensing boilers are very efficient. 95%.
old boilers and fires less so. about 70%.

you are talking about the power/capacity of the boiler. rated in KW.
the higher the number the more the boiler can do. ie more/bigger radiators.

retepetsir

Yes I know about efficiency in that sense (electrical engineer), but wondered if it was similar to electrical power supply systems....i.e. a supply may be 90% efficient but only when running at the designed load. I therefore wondered if running the Potterton Profile (75% efficient) at only half its designed capacity would bring its efficiency down?

Thanks for the help so far, karl-123, I've used an online calculator to work out that the one in the main bedroom (3m x 3.8m) is approximately 50% of the size it needs to be at a minimum (3 outside walls, older double glazing, etc), having averaged a number of calculators - 750W as opposed to a suggested minimum of 1600W...therefore it doesn't ever feel warm.

So as long as I'm within the 14kW limit for the boiler I should be fine, and currently being at 7.5kW (inc hot water and 10% losses) I'm nowhere near it.

Cheers

karl-123

older boilers multifunction gas valves,
can only be range rated manually, on the gas valve
governor on the actual boiler,the silver badge on the boiler,
will give boiler outputs, compared to mbar gas pressure at the burner,

more modern day boilers are " range rated "
the ch or dhw thermistors/thermostats are calibrated,
and work in conjunction with the gas valve,

unlike the older boilers that usually have low/med/high
outputs on the gas valve, the newer boilers

modulate to demand.....this helps with efficiency.
60% compared to 90% on average

:xmassign:

Ben84

I've found that older central heating installations often have what appear to be very undersized radiators. Generally people get around this by setting the boiler thermostat high so that the water going through them is hotter and they dissipate heat faster. This isn't going to be very energy efficient though and you may still struggle in very cold weather to reach the indoor temperatures you want to.

Upgrading to higher kW output radiators means you have the capacity available if needed when it's colder. You can fit thermostatic valves at the same time to avoid overheating when your heating needs are lower. Between these two upgrades you'll have more control over the heating and a much wider range of output.

I believe that you shouldn't fit thermostatic valves to every radiator however, the one in the room with the room thermostat should be fitted so it cannot be turned off and is controlled by the room thermostat only. You don't want the boiler switching on with nowhere for the heat to go.

As for the walls, are they cavity? If so it would be worth talking to the other people in the building about having them insulated.

retepetsir

Thanks Ben. The installation is probably only about 12 years old which is why itt surprised me, unless they were doing it on the cheap (used to have a hot air electric system fitted, some of the flats still use this). The cost of radiators seem pretty cheap now so I think its worth the upgrade.

The boiler temp is set at '5', the next setting is 'Max', so its pretty much as high as it can go which isn't good.

We already have thermostatic valves on the radiators but they seem pretty useless at the moment as the place never gets that warm. It sits at around 17C at the moment, and with the heating on full can only get to around 20C and that takes a long time with some very hot radiators!

Some of the walls are cavity, but the ones underneath each window are just single brick sections of 10cm so not overly useful. It's an odd design of a building (built it 1970). I'll propose that idea of cavity wall insulation but for the size of the building I reckon it'll be rather pricey.

Ben84

You would really need some insulation quotes and work out the cost between all the flats to decide if it's worth it. If it's a tall building scaffolding may be needed and that will add to the cost. However, once done it's permanent and will turn in to energy savings over and over again each winter. Insulated buildings are also more comfortable and I've found they get less mould patches on the walls. It's also good for the resale value of the flats. There are good selling points to getting it done.

I think I know the detail you mean under the windows. Are the radiators fitted against these sections? It's not great having thin poorly insulated walls anywhere, least of all behind your radiators. It may, particularly if you're replacing radiators currently blocking access to them be possible to put a sheet of thin high performance insulation board over them.

cyclonebri1

There is an ideal radiator for an ideal system run ideally.

But, balls, that doesn't happen.

Gone are the days when the engineer calc'd the rads for every room and supplied on that basis.

Today it's so much more simplified, guestimate based on 5 sepaerate systems for 5 types of house, extremes left out of course.


An undersized rad is just that, it will never heat the room it's installed in at the same time asd correctly sized rads in the same house at the same time.

So?, always ensure the rad is oversized, I sugest by at least 25%, possibly more, it can then be throttled down, but never throttled up.

The only downside is in the cost of the larger rad, which to be honest is negligiable.:)