Hello the stupid one here

[Britlee]

I'm pricing up a combi change and its my first one, I have just worked out all the room sizes and added them all together which can out at 9 kw. To me this looks low considering the size of the house, it has 13 rooms and 11 rads. As this is my first one i'm not shaw if this is normal. also the litres per minute is at 20.

Thanks Lee

 

[P4ULT]

i wouldnt worry about it to much most combi boiler will dish out 18-24kw to the heating as standard.

 

[SafeGasInstall]

combi on 11 rads in 13 room house ???? how many bathrooms are there ?

 

[dancinplumba]

is it a well insulated house ?

 

[Britlee]

Thank you i'm just a bit worried about getting the wrong boiler. The costomer works for a company how makes pro combi, so i'm looking thought the booklet he gave me for the DHW flow rate and it only tells me the min and i'm looking for 20 lpm. can you get a combi that will projuice that much hot water.

 

[SimonG]

As SGI asked how many bathrooms/showers?

 

[P4ULT]

i can say only one thing about pro combi they are total poo

 

[Britlee]

combi on 11 rads in 13 room house ???? how many bathrooms are there ?

11 rads as he has taken one out of the utility room and there is no rad fitted on the landing. he as one bathroom and en-suite which i explaned to him that a nomal combi would struggle with 2 bathrooms. But he said, thats okay there is only 2 of us that live here.

 

[Britlee]

I suggested he went with a system boiler.

 

[SafeGasInstall]

wb solution for you will be floor standing High Flow 42KW , make sure gas is min 28 all the way to boiler , never heard from this typr of boiler my self pro combi - what is it ?

 

[dancinplumba]

is he supplying boiler ?

 

[moony]

Pro combi are badged up ideals

 

[PlumbBobBob]

so not "ideal" then lol

 

[P4ULT]

Pro combi are badged up ideals

i neber knew this the ones i used although a couple ofr years ago dodnt look like any ideal i had fitted. which ideal is it

 

[kay-jay]

i thought they were vokera!

 

[doitmyself]

I have just worked out all the room sizes and added them all together which can out at 9 kw.

How did you work out the kW from the room sizes?

Use the Whole House Boiler Size Calculator but set the Domestic Hot Water allowance to 0 as you have a combi boiler. This will give you the total heating requirement, which you can compare to your 9kW.

also the litres per minute is at 20.

How do you know, have you measured it?

The Procombi Exclusive 24 provides 4.8 - 24.2kW for heating and 24.2kW for hot water. So your maximum flow rate will be only 9.9 litre/min for a 35C temperature rise. If the water is flowing through at 20 litres/min the temperature rise will be only 18C. If you really need a 20 litre/min flow rate you would have to install a 48kW combi boiler!!

 

[desrob]

your 9kw does seem low, but as stated a combi is well cabable,your main concern will be hot water l/min,20 is high so your looking at a big combi,what about a thermal store

 

[mfgs]

i thought they were vokera!

They are re-badged vokeras, I have had alot of dealings with them recently.

 

[moony]

Pro combi exclusive is identical to the idea c30 just different fronts

 

[Britlee]

How did you work out the kW from the room sizes?

Use the Whole House Boiler Size Calculator but set the Domestic Hot Water allowance to 0 as you have a combi boiler. This will give you the total heating requirement, which you can compare to your 9kW.


How do you know, have you measured it?

The Procombi Exclusive 24 provides 4.8 - 24.2kW for heating and 24.2kW for hot water. So your maximum flow rate will be only 9.9 litre/min for a 35C temperature rise. If the water is flowing through at 20 litres/min the temperature rise will be only 18C. If you really need a 20 litre/min flow rate you would have to install a 48kW combi boiler!!

I used the city plumbing heat loss calculator on all the rooms and added them all together which gave me 9kw and for the flow rate i used a flow cup and turned the kitchen tap on full. I suggested to the customer that it would be best to fit a system boiler but he's insistent on have a combi. I have no problem with the installation side of things its just the working out i'm not sure on, i just need to get this one out the way to boost my confidants.

Thank you all for your help.

 

[Deleted member 2053]

The room size calculation is irrelevant if you are keeping the existing radiators. If the customer is happy that all the rooms are adequately heated then go through and find the output for each rad and add them together. That is what you ae expecting the boiler to feed.

 

[Anton]

9kw is way too low for a house with 13 rooms. Some combis have a maximum heat output to radiators which is below the output to the hot water.
My 1947 house is 14 rooms (big rooms) and requires 30kw just for the heating. If the house is a fairly new well insulated property the the calculation will be lower. He may have taken radiators out, but what if he wants to put them back in in the future? I would double check the heat loss calcs for sure.

 

[doitmyself]

The room size calculation is irrelevant if you are keeping the existing radiators. If the customer is happy that all the rooms are adequately heated then go through and find the output for each rad and add them together. That is what you ae expecting the boiler to feed.

You are making the assumption that the existing radiators were correctly sized when installed and no changes have been made since then, e.g. improved insulation.

Rad sizing may have been done properly it was a one-off contract for an individual customer, but large housing estate contracts??

To give you a simple example, my house is 24 years old and on a small development of about 40 houses. Most of the radiators are under the windows and, without exception, they are all 600mm high and the same length as the window. The size was obviously chosen because it "looked nice", not because it was the size needed to meet the calculated heat loss. In fact some of them were double the required size. Now that the house has had uPVC DG windows, cavity and loft insulation fitted the total required rad size is 6.5kW, but I have 13kW of rads.

You should always do a Whole House Boiler Size Calculation first. (The [DLMURL="http://www.energysavingtrust.org.uk/england/Publications2/Housing-professionals/Heating-systems/Domestic-heating-sizing-method-2010-edition"]Latest Version[/DLMURL] has not been automated yet.)

It doesn't matter if the rads are oversized compared to the heat loss as it means the boiler will be able to run at lower temperatures with increased condensing, so more efficiently.

 

[Britlee]

You are making the assumption that the existing radiators were correctly sized when installed and no changes have been made since then, e.g. improved insulation.

Rad sizing may have been done properly it was a one-off contract for an individual customer, but large housing estate contracts??

To give you a simple example, my house is 24 years old and on a small development of about 40 houses. Most of the radiators are under the windows and, without exception, they are all 600mm high and the same length as the window. The size was obviously chosen because it "looked nice", not because it was the size needed to meet the calculated heat loss. In fact some of them were double the required size. Now that the house has had uPVC DG windows, cavity and loft insulation fitted the total required rad size is 6.5kW, but I have 13kW of rads.

You should always do a Whole House Boiler Size Calculation first. (The [DLMURL="http://www.energysavingtrust.org.uk/england/Publications2/Housing-professionals/Heating-systems/Domestic-heating-sizing-method-2010-edition"]Latest Version[/DLMURL] has not been automated yet.)

It doesn't matter if the rads are oversized compared to the heat loss as it means the boiler will be able to run at lower temperatures with increased condensing, so more efficiently.

Thanks for this. i have just filled in the whole house calculator and it comes out will 12.5kw, That looks better. As the flow is at 20 LPM could i fit a pressure reducing valve on the mains to lower the flow rate for a combi. I'm sorry to keep asking questions but i just want to get this right.

 

[Billy Bob Bob]

i though heatline made procombi?Manuals from Heatline Division, DD Heating Ltd | Find a Boiler Manual | gotoplumbing.co.uk