Boiler Sizing - Large 3 Bed House

[Sjrogers1]

Hi All,

Hoping to get some sound advice regarding combi boiler sizing for a large 3 Bed House.

We are refurbishing the house and plan to strip out the old boiler and pipework from the loft to relocate to the kitchen / diner whilst also renewing all copper pipework and installing new radiators.

We are also keen to future proof for a potential loft extension to come in the next 5-10 years which could potentially add 2 more bedrooms and a small en-suite shower room.

I've used 3 different BTU calculators online which based on my room sizes recommend the following BTU requirements per room

Lounge & Dining Room (we've knocked through): 14691
Hallway Downstairs: TBC - hard to calculate due to varying ceiling height and will also heat upstairs hallway - the neighbors have a radiator that gives out approx 6000 BTU
Kitchen: 10958
Our Bedroom: 5614
Bedroom2: 4105
Bedroom3: 2878
Bathroom: 2900

This equates to a total of 47.5 KW. Surely this doesn't mean that we would need a 47.5KW combi boiler? It seems excessive but as stated the BTU requirements are taken as an average from 3 different websites.

We do have a 5KW wood burner stove going in the Lounge / diner which could reduce requirements accordingly?

Plumbers that have quoted for the work are recommending between 33-38KW, Valiant Eco Tech or similar.

I've attached the floor plan to give you an idea of the scale of the house,

any advice you can give would be much appreciated,

Thank you

 

[ShaunCorbs]

It’s a no on the combi unless you are happy with just using one hot outlet at a time

But to answer your Heatloss questions if there correct then yes your load is 50k btu eg 15 kw

 

[king of pipes]

Viessmann 222 Shaunie ? Or it's a sealed system boiler viessman 200 35 kw and 300 litre unvented would be worth considering working on weather compensation , really depends on space you have ?

 

[Enthalpy]

One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. When used to measure an appliance, the term “BTU” actually refers to BTUs per hour (BTU/h).

One watt is one joule per second. It takes about 4.2 joules to raise the temperature of 1 gram of water by one degree Celsius.

One BTU/h is about 0.293 watts.

It appears that your total heat calculation is 13.81 kW.

BTU/h	kW
14,691​	4.30​
6,000​	1.76​
10,958​	3.21​
5,614​	1.64​
4,105​	1.20​
2,878​	0.84​
2,900​	0.85​
47,146​	13.81​

Combi boilers are sized for hot water flow.

 

[Steve ee]

One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. When used to measure an appliance, the term “BTU” actually refers to BTUs per hour (BTU/h).

One watt is one joule per second. It takes about 4.2 joules to raise the temperature of 1 gram of water by one degree Celsius.

One BTU/h is about 0.293 watts.

It appears that your total heat calculation is 13.81 kW.

BTU/h	kW
14,691​	4.30​
6,000​	1.76​
10,958​	3.21​
5,614​	1.64​
4,105​	1.20​
2,878​	0.84​
2,900​	0.85​
47,146​	13.81​

Combi boilers are sized for hot water flow.

Thanks for this

 

[gmartine]

As has been said you have your units mixed up so just divide your BTUs by 3.412 to get KW. Agree with recommendation of a Viessman 200W with WC as modulation is so good especially as you have a stove.

You could always bolt on an unvented cylinder afterwards when you extend as long as you have or leave room for it.

 

[DAVE01]

Well the first thing i would be doing is Looking at a Viessmann system Boiler and a unvented cyclinder and have the bedrooms on one circuit and the rest of the heating on another circuit as a matter of fact you can have independant hot water from a Visemann But another thing you should look at is a Insulation of all external walls this includes attic space and if possible under wooden floors if you have wooden floors down stairs And of course if you can change class in windows to trebble glazing . And look for any Grants you can get Hope this is of some Help