Oil boiler help please!

[jon26]

I am looking at a Worcester Greenstar Heatslave Oil-fired combi for our house, there are 3 different models (12-18, 18-25, & 25-32) they all offer different hot water flow temperatures, and it would be the larger 25kW - 32kW model that I would like to have due to the improved HW flow rate.

The question is, in the product info says '25kW' as a minimum output, what happens if only 1 or 2 radiators are calling for heat (there are only 9 radiators in the house and this is much lower than 25kW loading) maybe only 8-10kW instead. Will the boiler automatically adjust down like a normal boiler would.

Or I may have got this completely wrong... help please!!

 

[Agile]

I think that, unlike gas boilers, most domestic oil boilers dont modulate their power down.

If the demand for heat is very low then they accommodate that by only firing for a short time and then going off. This means they might run for just one minute in every ten.

This is rather inefficient and a hot water cylinder would in many ways be a better way to meet your requirements.

Tony

 

[jon26]

Thanks Tony

I think a combi boiler with only 1 bathroom is more efficient than a separate hot water cylinder, trying to maintain say 200 litres of hot water up to temperature instead of a combi where you heat only what you use.

 

[Agile]

You have missed the point!

Once the water in a cylinder is heated up the boiler goes off and the heat loss from the cylinder is very low ( about 2 kWh per day ).

For the six month heating season of the year, the boiler would be considerable less efficient if it was deep cycling on only about 10% of full load.

But its your house so you can choose what you want to ( and pay for the inefficiencies! ).

Tony

 

[Terrywookfit]

Do yourself a favour and buy a Grant.

The bloke who services it will be happy also.

What size bath have you got to need a 200l cylinder?
A 100l fast recovery is quite ample for most jobs!

 

[jon26]

You have missed the point!

Once the water in a cylinder is heated up the boiler goes off and the heat loss from the cylinder is very low ( about 2 kWh per day ).

For the six month heating season of the year, the boiler would be considerable less efficient if it was deep cycling on only about 10% of full load.

But its your house so you can choose what you want to ( and pay for the inefficiencies! ).

Tony

I do take your comments on board
There is no room for a separate cylinder and the capital cost is so much more. With the above comments in mind, I may opt for the mid-range size 18-25, therefore reducing the cycling times but still getting 18l/min HW

 

[transam]

Do yourself a favour and buy a Grant.

The bloke who services it will be happy also.

What size bath have you got to need a 200l cylinder?
A 100l fast recovery is quite ample for most jobs!

You would be well advised to take Terrywookfit's advice , buy a grant ! worcester oil boilers , bits of plastic , a tacky ally 2nd heat exc , dire things to work on , serviceing ect Turkeys !!

 

[petit_pablo]

Ive got the heatslave 18-25 here.

Hw is fine for 95% of the time. Depths of winter you really have to crank the stat up to get a good bath of water though, seems to OH occasionally if you leave it at that temp 24/7.

Servicing looks painful, mines been in 2 years and i really should do it but everytime i look in the case i just get depressed, usual worcester design under there.

Its had 1 breakdown already in the 2 years, the crappy plastic honeywell diverter seized in heating position. Good knows why though, system is crystal clean.

 

[Agile]

Space for cylinder in the loft?

 

[jon26]

Do grant make an external model?

 

[vulcancontinental]

Once the water in a cylinder is heated up the boiler goes off and the heat loss from the cylinder is very low ( about 2 kWh per day ).
Tony

I don't dispute this at all but I just wonder where you got that figure from.

I was thinking of contacting a manufacturer for their figures but you may have already done so.

Do you have other information on loss from DHW cylinders?

All information gratefully received from anyone.

David

 

[Terrywookfit]

Do grant make an external model?

Yes they do.
Check out their website. www.grantuk.com/ -

 

[Agile]

Once the water in a cylinder is heated up the boiler goes off and the heat loss from the cylinder is very low ( about 2 kWh per day ).
Tony

I don't dispute this at all but I just wonder where you got that figure from.

I was thinking of contacting a manufacturer for their figures but you may have already done so.

Do you have other information on loss from DHW cylinders?


David

CL300HE
CL250HE
CL210HE
CL170HE
CL145HE
CL125HE
CL70HE

Megaflo
Heat loss
in 24 hours
(kWh)
70 li 1.10
125li 1.49
145li 1.65
170li 1.77
210li 1.97
250li 2.09
300li 2.25

Its on the Megaflow web site. They have 50mm of insulation!

BTW I had guessed at that figure but its spot on for a typical cylinder size.

When the heat loss is so low you will understand if I sound a bit sharp to an OP who mourns the waste of energy keeping a cylinder hot all day.

The cost of keeping the cylinder hot is about 10p a day ! Thats 1/20th of a cheap pint of beer.

Tony

 

[slapper]

Only fitted one greenstar,bought by customer.Will never fit any again,piece of garbage.Get yerself an extrnal Grant combi.