rad sizing

[mkflow]

hi
does anyone have a quick method of sizing radiators for a new install as the whole house method takes a long long time

many thnaks

 

[ecowarm]

The quick way is 1000x600 Double for every room or you could try this, dont know if it will work in the forum.
If not Google "quick heatloss calculator"
[h=3]Quick Rule of Thumb Route| ^ top ^ |[/h]

1​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
2​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
3​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
4​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
5​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
6​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
7​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
8​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
9​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
10​	- Please Select -Living 60 W/m2Bathroom 70 W/m2Kitchen 60 W/m2Bedroom 60 W/m2Hall/Landing 60 W/m2​	​	​	0.00​	0.00​	0​
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Room
Room Type
Length (m)
Width (m)
Total
(m[SUP]2[/SUP])
HLoss (W)
HLoss (kW)​

 

[ecowarm]

It won't work in the forum

 

[doitmyself]

does anyone have a quick method of sizing radiators for a new install as the whole house method takes a long long time

There's not a "whole house" method for rad sizing, but there is a "whole house" Boiler Size Calculator. Using this should take less than 15 minutes. You have to deduct 2kW from the result to get the heating requirement.

Having found the heating requirement, it's just a case of dividing this between the various rooms, hall, landing etc. Assuming room heights are constant, you can base it on floor area.

For example:

If the total floor area is 100m² and the heat requirement is 10kw, a room with a floor area of 20m² will need a 10 x 20/100 = 2kw radiator. Obviously you will end up with required rad sizes which may not be actually available. Use the nearest size smaller for bedrooms, kitchen and toilets and the nearest size larger for all other rooms.

As the boiler will be a condensing type you should increase all rad sizes by 20%. This will allow the boiler to run with a 20°C differential; the rads should also be balanced with a 20°C differential. The reason for the 20% increase is that a radiator gives out about 15% less heat when it has a 20°C differential. (They are tested with a 10°C differential.)

 

[duff]

you can get a fantastic free app if you have a smart phone just put room sizes in and it does all the work for you.

 

[doitmyself]

you can get a fantastic free app if you have a smart phone just put room sizes in and it does all the work for you.

Be interesting to know what assumptions it makes.

 

[AWheating]

the rad calculator on the city plumbing website is very good and generally close to the values from longhand cals.

 

[fuzzy]

hi
does anyone have a quick method of sizing radiators for a new install as the whole house method takes a long long time

many thnaks

whole house does the boiler not the rads

 

[fuzzy]

Be interesting to know what assumptions it makes.

works well imo

 

[doitmyself]

whole house does the boiler not the rads

Agreed, but then all you have to do is divide the heat produced by the boiler between the rooms. See my earlier post.

The two basic "sins" are:

1. Sizing the boiler based on the previous boiler
2. Sizing boiler based on the total output of the existing rads.

Both methods assume: (a) the previous boiler/ rads were correctly sized; and, (b) no changes have been made to the house (insulation, DG windows etc) since the old system was installed.

 

[bengasman]

The two basic "sins" are:

2. Sizing boiler based on the total output of the existing rads.

Installer: "Mr Customer, are all your rooms warm enough?"
Customer: "Yes, why?
Installer: "Well, I'm sorry but my calculator says the rads have been wrong the past 10-20 years, so you'll have to fork out another grand to replace them"

When is the last time you actually had a customer that accepted that?

 

[kirkgas]

does anyone actually properly calculate rads, some people are aware of heat loss, to work out the heat required to replenish the lost heat, but say you work out a room needs 2.1kw, most people seem to simply then look at a rad sheet and find a 2.1kw rad, without taking the diversity factor etc into account, ie the delta T, (boiler flow+return/2-room temp) so it cant really be worked out properly without knowing the boiler info, the rad sheet info (that we dont read) will give outputs based on say delta T of 50 and flow and return from the same side but you need to recalculate for a different delta T and opposite end valves

 

[capitanpugwash]

does anyone actually properly calculate rads, some people are aware of heat loss, to work out the heat required to replenish the lost heat, but say you work out a room needs 2.1kw, most people seem to simply then look at a rad sheet and find a 2.1kw rad, without taking the diversity factor etc into account, ie the delta T, (boiler flow+return/2-room temp) so it cant really be worked out properly without knowing the boiler info, the rad sheet info (that we dont read) will give outputs based on say delta T of 50 and flow and return from the same side but you need to recalculate for a different delta T and opposite end valves

Yeah that's what I was going to say. Do that normally..... (whistling smiley with winkey face)

 

[doitmyself]

Installer: "Mr Customer, are all your rooms warm enough?"
Customer: "Yes, why?
Installer: "Well, I'm sorry but my calculator says the rads have been wrong the past 10-20 years, so you'll have to fork out another grand to replace them"

But if the rads are oversized, which is what you imply, there is no need to replace them. Oversized rads means that a correctly sized boiler can run with lower flow and return temperatures and still produce the correct amount of heat.

 

[doitmyself]

does anyone actually properly calculate rads?

I doubt if any more than 5% of domestic installers do that.

However, the new Guidance which came into force last October specifically says that systems "should be designed so as to provide low primary return temperatures, preferably less than 55°C, which maximize condensing operation."

This means that installers will have to know how to calculate the "oversizing" necessary for a radiator to deliver the required amount of heat when running at lower temperatures.

I know that, currently, installers are virtually free to do what they like, provided the boiler installation is notified to Building Control via Gassafe, but I have a feeling that it won't be long before they are asked to produce their calculations showing that the system has been correctly sized.

Don't forget that Building Control has the final say as to whether something meets Building Regulations.

 

[bengasman]

But if the rads are oversized, which is what you imply, there is no need to replace them. Oversized rads means that a correctly sized boiler can run with lower flow and return temperatures and still produce the correct amount of heat.

In which case there was no need to do the calculation to work out what size the rads should be.

 

[bengasman]

Don't forget that Building Control has the final say as to whether something meets Building Regulations.

Absolute and utterly complete nonsense.
I certify my work after it's finished. If some muppet from building control thinks he knows better, he will have to prove that. As every single lba inspector I have ever seen did not have more than the faintest idea what he was on about, the chances that a tribunal will ever rule against me, is infinitesimally small.

Where do get these pathetic tales from? You clearly have nothing to do with the heating industry.

 

[doitmyself]

Absolute and utterly complete nonsense.

I suggest you read the Domestic Building Services Compliance Guide 2010 Section 1.4 of which says:

1.4 Status of guide
Building regulations contain functional requirements (called standards in Scotland), such as requirements that buildings must be structurally stable, must be constructed and fitted to ensure reasonable levels of fire protection, and must be reasonably energy efficient.

These functional requirements are often drafted in broad terms, and so it may not always be immediately clear to a person carrying out work how to comply with the relevant requirements. Consequently, documents are often issued which provide practical guidance on ways of complying with specific aspects of building regulations in some of the more common building situations.

Those documents are called Approved Documents in England and Wales, Technical Handbooks in Scotland and Technical Booklets in Northern Ireland.
Approved Documents, Technical Handbooks and Technical Booklets are intended to provide practical guidance but they are not intended to be comprehensive. Consequently, they may contain references to other documents which will provide more detailed information and assistance on partsof the guidance.

This guide is one of those documents. It provides more detailed information on the guidance contained in Approved Documents L1A and Li B, Section 6 of the Domestic Technical Handbook, and Technical Booklet Fl about compliance with the energy efficiency requirements which applywhen installing fixed building services in new and existing buildings.

Note: Following guidance in an Approved Document, Technical Handbook or Technical Booklet does not guarantee compliance with building regulations.

If you follow the relevant guidance in an Approved Document, Technical Handbook or Technical Booklet and in any document referred to (such as this guide) which provides additional information to help you follow that guidance, there is a legal presumption that you have complied with building regulations.

However, in every case it is for the building control body to decide whether work complies with building regulations.

So, you should always check with the building control body before you start work what they consider it is necessary for you to do to comply with building regulations.

 

[bengasman]

If you actually try to understand what it says, you would notice or rather should notice that it mentions people not understanding, clearly pointing at guidance to the layman like yourself.

As I am authorised to sign work off myself, that clearly does not apply to professionals like me.

Apart from that, approved documents hold no legal status any more than British Standards do.

But by all means, if you enjoy looking like a complete idiot by trying to tell professionals how to do their job in disciplines you have never worked in, go right ahead handing out your misguided opinions.

 

[leelister6]

Was taught this method years ago and still works for me; measure room volume in feet, times by 4 to give btu requirement then add 20% (This is for a normal room i.e. no patio doors etc) If there are patio doors, bung on 50%. Never had a customer complain that the rooms not warm enough!

 

[doitmyself]

If you actually try to understand what it says, you would notice or rather should notice that it mentions people not understanding, clearly pointing at guidance to the layman like yourself.

Where does it say that?

The Guide is written for the professional, not for the householder.

As I am authorised to sign work off myself, that clearly does not apply to professionals like me.

Oh yes it does apply.

Apart from that, approved documents hold no legal status any more than British Standards do.

Approved Documents do have legal status; they get it from the Building Act 1984.

The problem is that they are only guidance. To quote from the Planning Portal website:

The Approved Documents are intended to provide guidance for some of the more common building situations. However, there may well be alternative ways of achieving compliance with the requirements. Thus there is no obligation to adopt any particular solution contained in an Approved Document if it is preferred to meet the relevant requirement in some other way.

The problem is that the Building Regulations are very general. For example Regulation L says:

L1. Reasonable provision shall be made for the conservation of fuel and power in buildings by:—

(a)limiting the heat loss through the fabric of the building;

(b)controlling the operation of the space heating and hot water systems;

(c)limiting the heat loss from hot water vessels and hot water service pipework;

(d)limiting the heat loss from hot water pipes and hot air ducts used for space heating;


You immediately ask: what do they mean by reasonable? So you refer to the Approved Document. But that's only guidance. You follow the guidance and produce what you think is a sensible cost-effective solution and pass it to Building Control for approval. They then turn round and say, "Sorry, that is not good enough, you can't do A and you have to do B and C."

You can then enter into negotiations with BC and, if it comes to it, you have the right of appeal to the Secretary of State.

 

[dontknowitall]

Was taught this method years ago and still works for me; measure room volume in feet, times by 4 to give btu requirement then add 20% (This is for a normal room i.e. no patio doors etc) If there are patio doors, bung on 50%. Never had a customer complain that the rooms not warm enough!

I do a similar calculation in metric and not had complaints either. Mind you last room I did was rather warm as I'd added too much extra for 2 windows, an open fire, and doors at either end of the room which would create a draught. No complaint from the customer though!

 

[mikegas]

I use an app on my phone which uses this formula, is this ok?

Measure the volume of room in cubic.ft.
i.e length x width x height.

Multiply by 5 for living rooms / dining rooms, 4 for bedrooms and 3 for anywhere else.

Add 15% for rooms facing north.

Add 20% for french doors.

Subtract 10% for double glazing and solid floors.

Subract 10% for uninsulated cavity walls and 20% for foam-filled cavity walls.

Add 15% for 2 outside walls, 40% for 3 outside walls.

This formula will give the required BTU for the radiator.