Choosing which boiler to attach to barrel

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Choosing which boiler to attach to barrel

Postby simonl on Tue Dec 04, 2018 7:23 pm


I have a late 1960's Aga. Born as oil fired. It's been very good, but the boiler has failed. It's a copper box that was strapped to the LHS of the barrel, feeding a large (recently replaced) direct HW cylinder.
It seems the copper heat exchangers / boilers are no longer available. It has to be direct HW suitable - so I believe my choices are
1. Build a new coppper boiler
2. Get a replacement cast 2 part boiler, with vitreous enamel lining
3. Get a stainless boiler made up.

Does anyone have any figures that state the heat transfer capacity of the boilers? Ideally something that compares the different materials. I want to chose the right one.
Aga say 1.1kW for the 90 Gal version & 1.3 kW for the 135 gallon version - but they can't tell me whether this is at min,max or nominal oil flow rates. They also don't say what the start & end temperatures are for the hot water. The factors clearly have a big impact on the output.

I did a simple excel table to get my head round some of the numbers, that might be of interest to some... It does not take efficiency into account - I have no idea what percentage of the heat goes up the chimney. Anyone know?

90 Gal 135 Gal 90 Gal 135 Gal
cc per min,cc per hour,litres kerosene per day, kWh per hour (i.e. kW!),kWh per day, Nominal water heating,Nominal water heating,% going to heating,% going to heating
4 240 5.8 2.35 kW 56 0.73 kW 0.87 kW 31% 37%
5 300 7.2 2.94 kW 71 0.92 kW 1.08 kW 31% 37%
6 360 8.6 3.53 kW 85 1.10 kW 1.30 kW 31% 37%
7 420 10.1 4.12 kW 99 1.28 kW 1.52 kW 31% 37%
8 480 11.5 4.71 kW 113 1.47 kW 1.73 kW 31% 37%

Many thanks.
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Re: Choosing which boiler to attach to barrel

Postby escort on Tue Dec 04, 2018 9:28 pm

Have you spoken to Barry at agafixspares? it is likely he could supply you with a suitable replacement or perhaps your copper one can be repaired.

Better still use the Aga as a cooker only and use a c/h boiler to heat the water.

Not sure about any figures regarding heat transfer as system design and positioning of pipes etc would all have a bearing this and outside conditions etc will all have a bearing on the output of a vapourising oil burner.
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Re: Choosing which boiler to attach to barrel

Postby john on Tue Dec 04, 2018 9:40 pm

I woud not look for figures on an Aga direct boiler. So much depends upon the way it is installed .
If you must have an Aga boiler (which will be inneficient) then go for stainless, and many other sources other than agafix will give a better deal .
As Escort says , better to leave out the aga boiler and produce your hot water from the CH boiler
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Re: Choosing which boiler to attach to barrel

Postby berby on Wed Dec 05, 2018 8:19 am

I have a s/s boiler as removed from an Aga converted to Electrickit. £50 + fedex, you can message me. However, i agree with John and Escort, for best efficiency let your oil boiler heat the water.
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Re: Choosing which boiler to attach to barrel

Postby simonl on Sat Dec 08, 2018 8:10 pm

Thank you for your responses so far.

There's seemingly a worldwide theme suggesting an Aga is not a great way to heat water. Here's my take, which I'd be keen to see what people's thoughts are:
Most of the time there's no cooking, and the kitchen is warm. Once the storage tank is up to temperature it reaches a state of equilibrium. No more (particularly) useful heat is being drawn from the Aga - Any heat leaving the Aga as hot water is simply being lost to the floorboards & the airing cupboard. My proposal is firstly to reduce the heat losses from the pipes & then divert spare heat elsewhere. I have a coil towards the top of my cylinder from which I can draw heat for towel rads. I appreciate I need to control this so that I retain enough hot water. There is no other source of heating other than a good wood burner.
My Aga has no thermostatic control - it's just open loop. So it doesn't 'know' whether or not I'm heating rads or not, the fuel use is the same, I believe.
I'm considering adding more thermal store capacity - with good insulation a 250 litre tank loses only 1kWh of heat over 24hrs. With an Aga putting out about 1kW of heat into the water that's 23kWh of heat stored & 1kWh lost, so 95% of it stored. Call it 80% after pipe loses etc - that's lots of useful heat: Several big radiators for a few hours.

Am I alone in this train of thought? Where's it flawed? There's always someone else smarter on the internet to add value to an idea (or trash it!).

I'd really appreciate people's thoughts.
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