Allowances for Rad Sizing for a Room With ..

[DIYWell]

I've looked at a few rad size calculators online. Naturally nothing I've found quite fits the room I'm looking at.

So, what extras are usually added for a room that ...
Is north facing and rarely had any direct sunlight on it?
Has a roof window in it?
Has a pitched warm ceiling?

Is there a rule of thumb or is there a (free) specialist calculator that lets these factors be taken into account?

 

[bengasman]

You can try to calculate the "exact" size required, as was needed in the olden days when the only control was a mechanical roomstat in the hall.
With the arrival of more sophisticated controls, the need to size precisely has become obsolete.
I always recommend my clients to choose a rad that is significantly larger than the old calculations indicate.

1. Condensing boilers increase in efficiency with increased rad sizes.
2. Rads on condensing boilers need an increase in size compared to the old calculators due to lower temperatures.
3. An "oversized" rad reduces the warm up time of a room which adds to comfort.

Would you buy a car that can not go above 70 because that is the speed llimit?

 

[DIYWell]

That goes against most of what I've been told. Condi boilers work efficiently then the temperature difference is about 20. If you just bang in big rads you end up being inefficient in my opinion.

Also, if big rads was the answer, they'd come in three sizes and all calculators would agree.

Clearly it's more complicated to work out if you want to run a heating system efficiently.

 

[bengasman]

That goes against most of what I've been told.

How many of the people that told you the opposite have their energy efficiency qualification?

Condi boilers work efficiently then the temperature difference is about 20.

Nope, the temperature difference is irrelevant; the only thing that counts is the return temperature.

If you just bang in big rads you end up being inefficient in my opinion.

Why would that be inefficient?

Also, if big rads was the answer, they'd come in three sizes and all calculators would agree.

Nope, hundreds of different variations in heat demand, and lots of installers and designers try to up their profit margin by saving every penny possible and will therefore go for the absolute minimum required.

Clearly it's more complicated to work out if you want to run a heating system efficiently.

Nope, it is complicated if you want to work out what the very cheapest way is to comply with the regs. Just making it efficient is very simple.

 

[doitall]

You can try to calculate the "exact" size required, as was needed in the olden days when the only control was a mechanical roomstat in the hall.
With the arrival of more sophisticated controls, the need to size precisely has become obsolete.
I always recommend my clients to choose a rad that is significantly larger than the old calculations indicate.

1. Condensing boilers increase in efficiency with increased rad sizes.
2. Rads on condensing boilers need an increase in size compared to the old calculators due to lower temperatures.
3. An "oversized" rad reduces the warm up time of a room which adds to comfort.

Would you buy a car that can not go above 70 because that is the speed llimit?

Almost word for word what thescruff said on another forum Ben

 

[bengasman]

Got to be right then.

 

[Foobix]

You can try to calculate the "exact" size required, as was needed in the olden days when the only control was a mechanical roomstat in the hall.
With the arrival of more sophisticated controls, the need to size precisely has become obsolete.
I always recommend my clients to choose a rad that is significantly larger than the old calculations indicate.
1. Condensing boilers increase in efficiency with increased rad sizes.
2. Rads on condensing boilers need an increase in size compared to the old calculators due to lower temperatures.
3. An "oversized" rad reduces the warm up time of a room which adds to comfort.

Would you buy a car that can not go above 70 because that is the speed llimit?

Almost word for word what thescruff said on another forum Ben

Or plagiarism more like,lol
Do you not agree that condensing boilers heat radiators/rooms a lot quicker due to the efficiency of forced draught burners and heat exchanger design?

I always recommend my clients to choose a rad that is significantly larger than the old calculations indicate.

I think you would need to because of the new,lower temp in heat loss calculations.
While i agree with you that slight over sizing will ensure the desired temperature requirements are met,over sizing to make the boiler run more efficiently is nothing more than false economy.

 

[bengasman]

...Do you not agree that condensing boilers heat radiators/rooms a lot quicker due to the efficiency of forced draught burners and heat exchanger design?

Certainly not. The speed of radiators heating up depends on the capacity of the boiler and pump relative to the rad output. A boiler with an output of 20 kW and 40% efficiency ( about as low as you can get ) will heat the rads just as fast as a boiler with the same output but 90% efficiency ( about as high as you can get ).

I always recommend my clients to choose a rad that is significantly larger than the old calculations indicate.

While i agree with you that slight over sizing will ensure the desired temperature requirements are met,over sizing to make the boiler run more efficiently is nothing more than false economy.

How would that be false economy? The larger the rad ( though not unlimited of course ) the lower the boilerstat can be set, and this improves the amount of heat recovered from the combustion.

An added bonus is that especially small rads are hard to tune to a low return temperature. The ( too ) high return temperature exacerbates the problem of boilers running in non condensing mode due to the user setting them too high in order to get the house warm e.g. flow temp of 80C. When the small rad only has a Delta t of 10, the return temp coming back at 70 in stead of 55 or lower “disables” the condensing mode raising the gasbill by up to 10%.
At the current ( and continually rising ) gasprices, 10% of the annual gasbill will soon amount to more than the extra cost of the larger rads.

 

[Foobix]

...Do you not agree that condensing boilers heat radiators/rooms a lot quicker due to the efficiency of forced draught burners and heat exchanger design?

Certainly not. The speed of radiators heating up depends on the capacity of the boiler and pump relative to the rad output. A boiler with an output of 20 kW and 40% efficiency ( about as low as you can get ) will heat the rads just as fast as a boiler with the same output but 90% efficiency ( about as high as you can get ).

I always recommend my clients to choose a rad that is significantly larger than the old calculations indicate.

While i agree with you that slight over sizing will ensure the desired temperature requirements are met,over sizing to make the boiler run more efficiently is nothing more than false economy.

How would that be false economy? The larger the rad ( though not unlimited of course ) the lower the boilerstat can be set, and this improves the amount of heat recovered from the combustion.

An added bonus is that especially small rads are hard to tune to a low return temperature. The ( too ) high return temperature exacerbates the problem of boilers running in non condensing mode due to the user setting them too high in order to get the house warm e.g. flow temp of 80C. When the small rad only has a Delta t of 10, the return temp coming back at 70 in stead of 55 or lower “disables” the condensing mode raising the gasbill by up to 10%.
At the current ( and continually rising ) gasprices, 10% of the annual gasbill will soon amount to more than the extra cost of the larger rads.

Certainly not. The speed of radiators heating up depends on the capacity of the boiler and pump relative to the rad output. A boiler with an output of 20 kW and 40% efficiency ( about as low as you can get ) will heat the rads just as fast as a boiler with the same output but 90% efficiency ( about as high as you can get ).

That's a joke,right?


I do know how a condesing boiler works and how it should be commissioned to achieve good efficiency,so please do not quote your pedantic rubbish in an attempt to flatter yourself.

 

[bengasman]

...Do you not agree that condensing boilers heat radiators/rooms a lot quicker due to the efficiency of forced draught burners and heat exchanger design?....

.....That's a joke,right?


I do know how a condensing boiler works and how it should be commissioned to achieve good efficiency,so please do not quote your pedantic rubbish in an attempt to flatter yourself.

Judging by the questions you have asked, and the remarks you made, you only have a rudimentary understanding of the how and what concerning condensing boilers.

As with most things, you can argue of what I consider the best method can be improved upon or not.
Whether or not my comments are essentially correct without trying to figure out which is the best method and which is second best, can not be denied.

 

[Foobix]

I bow to your superior knowledge oh master.
Please,just one thing,enlighten me.
I do not understand how a boiler with an efficiency of only 40% can match a similarly rated appliance with an efficiency of 90%?
If 60% of the heat is lost on this band 'K'(it must be 'K' mustn't it?)appliance,whilst only 10% is lost on the band 'A' rated appliance.
50% more heat being delivered in heat transfer to the radiators yet you state the systems will reach a set temperature at roughly the same time.
Now i know in your opinion you have a superior knowledge and to be honest i might have to agree.However,i will reserve judgement until you come back to me with facts and figures to back up your statement.

 

[bengasman]

It would appear you missed the word output
As with cars, the performance is defined by how many kW comes out of the engine, not how much fuel you burn. As such, I only use the output in my calculations, not the input.

 

[RichieHoneybucket]

It would appear you missed the word output
As with cars, the performance is defined by how many kW comes out of the engine, not how much fuel you burn. As such, I only use the output in my calculations, not the input.

A car's performance is based on horse power Ben son. You're talking out your a.se mate. You've clearly been reading the wrong books mate, and you know SFA about boilers. What about a system by-pass??!!!

 

[bengasman]

The SI unit for power in automotive engineering has been the (kilo) Watt since before I studied engineering back in the seventies. Rather odd that anyone who claims to be an engineer would not be aware of that.

 

[ray99]

The SI unit for power in automotive engineering has been the (kilo) Watt since before I studied engineering back in the seventies. Rather odd that anyone who claims to be an engineer would not be aware of that.

As a motor vehicle technician of some 38 years that is correct. I think it was the Germans I first saw using kW instead of bhp. You can also use PS a a measure of power.
Incidentally a kW is about 1.34bhp.
Sorry to interupt your argument.