# Radiator size in living room - slow heating

I have recently moved and the living room seems to be taking an excessively
long time to heat up compared to the rest of the house.
The raditaor is a basic double panel 700 high by 1100 across without any
conventor panels or fins whatsoever. I am therefore unsure what the BTU of
such a radiator is, as Myson etc dont seem to produce a finless radiator.
The room is approx 14ft x 12ft, adjoing the linking between the hall and
kitchen. House is cavity wall (filled).Two sides are internal walls, one is
the adjoining neighbour and one is an outside. Room faces west/southwest
direction.
There is a pvcu window (double glazed window and door) that is equivilent to
Floor is laminate on a suspending wood floor (doubt it is insulated), and
there is a Baxi gas pebble effect fire in the room (i.e chimney losses).
Is the radiator I have sufficient to heat this size room? What would be the
recommended output to change to if required?
Check that the radiator is getting as hot as the others - ie flow is okay.
If the room does get up to temperature eventually, the easy option is just to replace the existing rad with a double panel convector version of the same size.
Otherwise consider adding another physically small radiator on the opposite side of the room to help reduce cold spots. If a quick warmup of the living room, maybe when you get in from work, is a priority then dont worry about having too much heat output ; TRVs will take care of the temperature control. See what size fits in to the room layout and unless you really need to keep the depth (off the wall) to a minimum go for a double pamel convector.
In an earlier contribution to this discussion,
The rough rule of thumb which I use for calculating the output of double unfinned radiators is 2170 watts per square metre at a delta-T [1] of 60 degC. That would make your rad worth about 1670 watts - but you probably need to downrate that by up to 20% (to about 1340 watts) to allow for a likely lower delta-T value.
In order to work out whether this radiator is adequate for supplying heat at the rate at which is being lost to the outside world, you will need to do some proper calculations. You *could* do that with pencil and paper or a spreadsheet if you work out the areas of all the relevant surfaces, and look up the U values - but an easier way is to use a heatloss program such as the one which you can download from
your room isn't getting hot, it will be down to either or both of 2 causes: * the radiator isn't big enough (doing the calcs will check on this) * the radiator isn't getting its fair share of heat from the boiler - requiring the system to be balanced, and/or the thermostat(s) to be adjusted.
With regard to the second possibility: Is the radiator getting as hot as those in the other rooms? How long can you hold your hand on it? Is it getting hot as *fast* as the others? Is the heating being turned off by a room stat elsewhere before the lounge gets up to temperature?
[1] Delta-T is the temperature difference between radiator (average of input and output) and the room. If, for example, your flow temperature is 80 and return 70 (mean 75) and the room is at 20 degrees, the delta-T value would be 55 - which is probably the highest you are likely to achieve
Rad heats are fast as others in the house, and gets very hot (touch for about 1 second). At the moment I am running the lounge rad without the TRV set to max, and the house room stat in the lounge to make sure that it is not the room stat.
I have tried the heatloss program, but I am not sure what to enter for the Gas Warm allowance, or the Airchange rate. I have selected Gas Warm allowance as YES and a air change rate of 1.5? This returns a value of 1866 watts. Assuming the gaswarm allowance and air rate changes are correct this appears to show that the current rad is underated by around 25%
By using the same size rad, in a double panel 2 fin conventor should acheive about 2150 watts, which give around an extra 650watts and should be overated by about 15%.
Maybe, but only underated by that amount at the design external temerature, -1deg say, so if you have frequently noticed the rad ineffective at higher external temperatures there is something else. The lack of fins changes the balance between radiated and convected heat. I think its the lack of convection you are noticing. From one I have done before a double convector of the existing size will easily do in a modestly insulated room of that size. Since it was the comparison with other rooms you complained about its still well worth doing the whole house calcs to ensure a well balanced design.
Jim A
In an earlier contribution to this discussion,
Not sure I understand the TRV comment. Are you saying that the TRV *is* throttling the flow? If so, set it to max, or remove the head completely.
Looking at my radiator catalogue, I guess that 2150 watts for a double-finned 1100 x 700 is based on a delta-T of 50, whereas you may be able to achieve 55 and wring a bit more out of it.
Is your 1866 watts heatloss the steady-state value - or does it have any bunce in it (typically 10 - 20%) to provide a fast warmup? Provided there *is* some bunce, and provided the boiler and pipework can deliver the extra heat fast enough, this rad may well be ok.
It's worth trying a few different values for some of the parameters in the heatloss program to see what difference it makes. For example, what is the effect of saying NO to Gas Warm allowance, or going for 2 air changes per hour? [1.5 is probably ok unless you've got a lot of draughts - but it's always useful to know how much you've got in reserve in case any of your assumptions are wrong!]
Roger, this is a really useful estimated output value for older radiators. I'm currently updating/adapting a 1970's heating system, and will need to calculate the total load to allow for an extension as well - hopefully NOT a new boiler for now.... Most of my current radiators are single unfinned, and I wonder if you have a similar rule of thumb value for these?
Regards,
Charles F
In an earlier contribution to this discussion,
The value I use for single unfinned rads is 1280 watts/M^2 (taking the area as height x width, not total surface area of both sides). This is again at a delta-T of 60 degC, and should be multiplied by 0.9 for 55 degC or 0.8 for 50 degC.
[I have arrived at these figures by taking the values which I used back in 1969 when installing central heating in my first house - and converting from imperial dimensions, BTUs and temperatures in degF!]
For single finned rads, I use 2000 watts/M^2 at a delta-T of 60 (taken from a recent Stelrad catalogue). Its interesting that a single finned rad produces nearly as much output as a double unfinned one - due to the considerable increase in surface area provided by the fins.
For completeness, values for double rads with single fins and double rads with double fins would be about 2790 and 3575 watts/M^2 respectively (both at a delta-T of 60 degC).
Great set of figures. My first central heating project was around 1980, but unlike you I neglected to keep the paperwork! Now back to the calculator......
Thanks again, Roger
Charles F

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