Will Worcester Bosch Ri15 provide enough heat?

[Madmog]

My mother has a three bedroomed bungalow (10 radiators). She has had a quote from an engineer who will install a Worcester Bosch Greenstar Ri15 (which provides minimum output of 5kw, maximum 15kw heat) which she would like to accept. Can anyone tell me if this will provide sufficient heat for a house this size?

 

[fatplumber]

Should do it but if she is on her own then she should really think about a combi. It will save her a lot on hot water.

 

[bengasman]

It depends on the size of the rads. See FAQ for boiler sizing

 

[D_Hailsham]

Use the EST Boiler Sizing Wizard to find out what size boiler your mother needs.

The problems with sizing based on existing radiators are:

* You do not know how accurate the original sizing was. Many were just based on guesswork.

* Things may have changed since the rads were installed - insulation,double glazing etc.

Having found out what size boiler you need, use the Stelrad Elite Catalogue to find out the approximate output of all your rads.

If the rads total less than the recommended boiler output. it may be worth changing some rads for larger ones. But, if the rads add up to more than the boiler there is no need to do anything.

While the boiler is being changed the installer should also put thermostatic valves on all rads, except the one where the wall thermostat is located.

 

[bengasman]

The problems with sizing based on existing radiators are:

* You do not know how accurate the original sizing was. Many were just based on guesswork.

Be that as it may, I don't see people suddenly start changing rads because a table says they should. If the heating was insufficient, they would have changed the rads by now.

There is also a rather big problem using these stupid sizing methods: If you add up all the allowances and additions and extra percentages, you have added somewhere in the region of 30 % on top of what you need. I have never actually calculated a rad, just an educated guess, and I have never had complaints.

So unless people actually rip out all the rads and replace them with what it says in the tables, the heatloss calculation is completely pointless.

 

[D_Hailsham]

There is also a rather big problem using these stupid sizing methods: If you add up all the allowances and additions and extra percentages, you have added somewhere in the region of 30 % on top of what you need.

I don't know where you get 30% from! The only extra normally added to the calculated rad size is an allowance of 10-15% for heating up from cold. This is applicable if the house is frequently empty during the day - occupants at work - and heating is only used for a short time in the morning and in the evenings. But if the house is permanently occupied, there is no real need to add on anything to the calculated rad size.

I have never actually calculated a rad, just an educated guess, and I have never had complaints.

Old school, eh! Bet you were around when central heating was first being sold to the masses with by-lines such as "guaranteed temperatures". This was done by oversizing the radiators and , consequently, the boiler.

So unless people actually rip out all the rads and replace them with what it says in the tables, the heatloss calculation is completely pointless.

So there is a house with 20kW of installed rads, which now needs only 10kW as it has been fully insulated, double glazed etc. Along comes Mr Old School Heating Engineer and installs a 20kW boiler. The boiler modulates down so it will deliver the 10kW really needed. Rad temperatures are nothing like the 75-80°C but more like 50-60°C. Thats fine until it gets warmer. Tthe boiler can't modulate low enough, and the customer begins to wonder why he is not saving so much money on his gas bills as he was expecting.

 

[Agile]

I expect the 15 Ri will be totally adequate!

There is a whole raft of people, many with vested interests, who will encourage you to have a larger boiler than you need. Manufacturers, merchants, builders and heating installers.

Your installer clearly understands the need to fit the minimum size boiler to meet the demand.

Boilers are sized to meet the demand when its -1 °C outside. Thats usually less than 10 days a year! For the other 355 days the boiler is working at less than full capacity and less efficient.

Tony

 

[D_Hailsham]

I expect the 15 Ri will be totally adequate!

Your installer clearly understands the need to fit the minimum size boiler to meet the demand.

He may even have used the Sedbuk/EST calculator to find out what size is required

Boilers are sized to meet the demand when its -1 °C outside. Thats usually less than 10 days a year! For the other 355 days the boiler is working at less than full capacity and less efficient.

The 15Ri goes down to 5kW so, asuming all 15 kW is need for -1°C, it will be able to modulate until the external temperature reaches 13°C. Any higher and it goes into on/off mode.