Calculator recommendations????

[Riley]

Good afternoon I hope you’re well

I am trying to prove to a customer that their boiler is undersized. They have 20 radiators mostly doubles and a 220 L unvented cylinder. 18kw Worcester heat only boiler. Three years old.

I am trying to reverse calculate the heat requirements of the radiators that have been installed and I wondered if anyone had any calculator/app recommendations that might help with this?

Thanks

 

[ShaunCorbs]

Mr combi heat loss

Cylinder alone will want 10kw

 

[Riley]

Sorry Shaun I lie with fork tongue it’s only a 150L but that’s still gonna be 3-5Kw

 

[ShaunCorbs]

Sorry Shaun I lie with fork tongue it’s only a 150L but that’s still gonna be 3-5Kw

I would say / allow 8

 

[Riley]

Likely. Good little calc that

 

[townfanjon]

Personally I just base the rads off an old radiator catalogue. I did one recently and ended up with nearly 30 Kw load on just the rads .

 

[chris watkins]

Why would you size for heating & HW to be on together (at least first thing) ??

 

[Riley]

Well you need to have the option don’t you

 

[Harvest Fields]

I would say / allow 8

I always thought it was 8 upto a 200L cylinder.

 

[ShaunCorbs]

In the middle of winter it’s bound to come on together

 

[chris watkins]

In the middle of winter it’s bound to come on together

Why ? if timed.

 

[Harvest Fields]

What if they are timed to come on at the same time?

 

[chris watkins]

Well you need to have the option don’t you

I would say no, it is either but not both together. When the standard cylinder can take 18 - 20kW on its own you are never going to be able to do both successfully especially first thing in the morning when the heating load is so high.
If you dedicate all the boiler power to heat the cylinder your 18kW should heat the cylinder in around 30mins then shut off & give all the power to raising the house heating system up to running temperatures.
Once there it is not so much of a problem if it tops up. Time control is key.

 

[ShaunCorbs]

Why ? if timed.

In winter normally water comes on from around 6 same with heating so you would need hot water on from 5

 

[Last Plumber]

Good afternoon I hope you’re well

I am trying to prove to a customer that their boiler is undersized. They have 20 radiators mostly doubles and a 220 L unvented cylinder. 18kw Worcester heat only boiler. Three years old.

I am trying to reverse calculate the heat requirements of the radiators that have been installed and I wondered if anyone had any calculator/app recommendations that might help with this?

Thanks

I use this to sort work that out. If we mean the same thing?

 

[SimonG]

Heat water outside peak heating times.

Back to Rileys original question. Would you not be better just doing a quick full house heat loss calc?

 

[Welder]

100% a proper full calc to demonstrate your professional skills.
100% no reason whatsoever NOT to have an uvc come on before heating and to top up when not on. Only a fool wouldn't.

 

[chris watkins]

Back to Rileys original question. Would you not be better just doing a quick full house heat loss calc?

http://www.domestic-gas.co.uk/documents/CE54.pdf
This was designed to do just what you want. i.e. it provides a total heating load for sizing boilers without the need to do room by room full calculations as you would for heat emitters.

PS. you can take a view on whether you allow 2 or 3kw for DHW, personal I don't.

 

[Last Plumber]

I would normally calculate the heat loss from the house and also use the chart I linked to, to work out what they have now and what they need. That way you show them the full picture.

 

[Ric2013]

8kW for any cylinder up to 200l Sounds excessive IMO.

My own boiler is only 8kW and will heat the cylinder from cold for around 20 minutes and then starts cycling. In practice, we tend to reheat cylinders before they are stone cold, so I can't see a cylinder accepting 8kW very often.

 

[Harvest Fields]

8kW for any cylinder up to 200l Sounds excessive IMO.

My own boiler is only 8kW and will heat the cylinder from cold for around 20 minutes and then starts cycling. In practice, we tend to reheat cylinders before they are stone cold, so I can't see a cylinder accepting 8kW very often.

Just what I was always told and what I now work to mate.

 

[Ric2013]

Just what I was always told and what I now work to mate.

I've been told all sorts of things, including that if you have a 22mm pipe from the hot outlet of a combi, then you'll have reduced flow to the bathroom because 'the water slows down when it hits the 22mm pipe'.

Hence why I need to understand everything and why I question things.

In a 2 bedroom house with 5.5kW heat losses at design temperature, you'd specify a system boiler capable of providing 13.5kW at whatever flow and return temperatures you have decided on? Is that right?

 

[Harvest Fields]

No. Because clearly a 2 bedroom house wouldn’t have. A 200 litre cylinder.

 

[Ric2013]

Sorry, I read 8kW for up to 200l. What would you allow for a standard 117l cylinder then? <8kW, presumably?

 

[ShaunCorbs]

8kW for any cylinder up to 200l Sounds excessive IMO.

My own boiler is only 8kW and will heat the cylinder from cold for around 20 minutes and then starts cycling. In practice, we tend to reheat cylinders before they are stone cold, so I can't see a cylinder accepting 8kW very often.

Unvented cylinder?