Heat loss margin for error

[Antony Gelberg]

Hi all,

I hope this post isn't too scant on detail. I have established that my lounge / kitchen requires 12460 BTU for central heating. Interestingly, this is more or less the same whether I use the Myson program on Windows, or the plumber merchant method of volume in cubic feet x 5.5.

I'm after two vertical, so-called designer radiators, but they mostly seem to max out at just below the required figure.

The property is a 20 year old middle-floor flat, concrete framework in the block, pretty well insulated, so it seems. I never really turned my thermostat above 18/19 celsius in winter with my previous boiler and rads. I typed a figure of 21 degrees into the Myson calculator, as it was the default and I didn't want to live on the edge.

Is it likely that if I specify a couple of 5900 BTUs rather than 6230s, the 5% loss in maximum output would make any practical difference?

Antony

[Jonathan Schneider]

What, per hour ? For the rest of your natural life ?

Jon

[Andrew Gabriel]

You may find it's more than 5%... Power output of radiators is often quoted at higher water temperatures than are commonly used, certainly with condensining boilers, and also with convensional boilers in many cases. So you may find that on your system, they are less than 5900 BTUs/hr anyway.

Undersizing a radiator will result in the room taking longer to heat up from a cold start, and struggling to maintain temperature on the coldest days. It will also reduce boiler efficiency in most cases.

Unfortunately, radiators largely fit into the functional or decorative categories, with very little overlap. One possibility might be to add a functional radiator somewhere less obtrusive in the room, and it probably won't need to be very big.

[The Natural Philosopher]

Mmm. Depends on the margin of comfort the programs have built in.

I have one room that needs allegedly 1.5KW to heat it and has a 1.5KW fan blown radiator in it. Its not enough..well it might be in an infinitely long period of time, but in reality I plug in an electric heater fir ten minutes and its warm, and then the 1.5KW can just keep it warm if left on continuously (in darkest depths of winter that is)

Radiator over supply just means the thing warms up quicker, assuming you have TRV's or similar.