specifying radiator outputs

whitewash

whitewash

Fishy Fingers
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Hi folks

We have just had an offer accepted on a house which needs alot of modernisation. one of these things is to install central heating as at the moment it does not have any installed.

i have trawled the internet for calculations to work out the outputs required for different rooms and different room sizes but the different internet sites seem to give widely different results from the same raw data. does anyone in the business have a particular formula they use?


im not attempting to do the entire install myself, just getting a feel for things with a view to either doing some of the work myself OR buying the bulk of the hardware myself and getting someone in to install it.


any suggestions folks?
 
I would not get too bogged down in calculating the sizes and numbers of radiators, as a rule of thumb I was told to allow 5000 btu's per average size rad in calculating the size of the boiler so just make sure the boiler is big enough. you will be fitting thermostatic valves in any case so you will be manually setting the amount of heat available to each room. I have 9 rads of various sizes in my house all double convected and my boiler is rated at 60,000 output.

That does not specifically answer your question but hope it is of some help.
 
Look at the B&Q web site it has a chart on there you can use.
Different rooms have different ratings

use this

spike
 
This may help.






D'Oh! I have been Spiked.
 
Sure an expert will be along soon and tell you quickly in a couple of sentences how to work it out the way the way they do it.:)
 
thanks folks, going to be getting a good boiler, my parents have had nothing but trouble with the glow worm boiler they had fitted, i think the local BG fitter knows where the teabags and cups are in their house hes been that often!

worchester bosch seem to be the ones to go for on all accounts (correct me if im wrong!)
 
Worcester Bosch
Ideal
Vaillant

Would be the top 3 in my experiance.
 
It's a long time since I did this, but, basically it's a matter of working out the room heat loss at the lowest anticipated outside temperature, then getting a rad to replace this heat.

It is possible to go into great detail with all the differing surface areas / heat losses, but in practise you can only get rads of a certain sizes anyway so you just pick the next size up.

As has been mentioned most rads will have a TRVs fitted and most of the year (hopefully) the outside temp will be above freezing, so you could get away with smaller rads most of the time.
 
Don't bother specifying radiator sizes. When you get a quote specify that on acceptance of the quote that you require a copy of all heat loss calculations before the job proceeds. Ideally the radiators should be sized with a temperature differential of 20C to make the most of modern high efficiency radiators but this can often make the radiators larger than is practical so most people will size using an 11C differential.

The radiators should be sized to provide comfort temperatures depending on usage of the room. Living rooms are generally 21C, bedrooms 18C and bathrooms 22C. Before room stats became normal fixture hallways used to have radiators sized to provide 16C but they are more often assumed to be 18 or higher nowadays as the room stat is regularly in the hall. I prefer the room stat in the lounge as it makes sense to me to have the most control in the area where you spent more time sitting.

With the advent of radiator thermostats radiator sizing has become less critical but oversizing radiators is an unnecessary expense. A big advantage of TRVs is the ability to have radiators suitable for multiple use rooms. A bedroom/study can be heated to a comfortable temperature for studying but the TRV turned down to provide a more comfortable sleeping environment.

You need to give some careful though as to what sort of heating system you want.

A combination boiler will give a good system but with some limitations. Hot water flow rate is limited and all but the largest boilers will only feed one hot water outlet adequately at one time. You also need to ensure that the cold mains flow (not pressure) is adequate to provide the required performance. As a rule of thumb I generally say that the flow rate of the incoming main should be at least twice that required by the combination boiler. For good hot water performance the boiler should be as close to the outputs as practical. If the boiler is fitted at the opposite end of the house to an outlet there will be a long delay for hot water, reduced temperature due to cooling along the way and the subsequent waste fo water.

IMHO the best system is an unvented hot water cylinder combined with a sealed heating system. Providing cold water flow rates are good enough this will provide hot water to multiple outlets and, if a secondary circulation system is used, can be sited at a distance from the outlets.

If cold mains pressures are low you need to look at fitting a conventional system with tanks in the loft.

For boiler choice at the moment the Ideal Logic plus range are a good boiler and come with a 5 year warranty.

Check carefully before buying materials yourself. Heating installers will generally get better prices on materials and will charge a premium for fitting materials supplied by others. When I was pricing work for the family business if someone wanted to supply their own materials I would also specify that any delays caused by faulty/missing materials would be charged as extra. i would also not guarantee the materials and any breakdowns in the warranty period due to faulty materials would be chargeable. The extra discount that tradesman get gives them a buffer to allow for extra time spent dealing with faulty goods.
 
Thanks mike, very useful.


The house already has a hot water only boiler and our plans don't really allow the space for a hot water cylinder so we are limited to a combi setup. Boiler will be about q metre horizontally from the kitchen tap and about the same plus vertical from the bathroom.


Good points about the issues with self supply. Might just work out easier in the long run to get the whole job done by a pro and concentrate my efforts elsewhere.
 
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