Worth replacing an old oil boiler?

A while ago I asked about the possible perils of buying a listed house (17thC timber-framed) - the survey results were so bad that I ran away bravely. It now seems likely that I'll be buying an unlisted 1930s "arts and crafts" style house that seems to be pretty solid (but the survey is next week - :eeek!). This house has a fairly old (20+ years?) Mistral oil-fired boiler, which is certain to be non-condensing. I need to check but I think the output is 160k BTU. My previous boiler experience has all been with gas boilers. What do I need to know that I may not know? What real world efficiency savings am I likely to get by changing it for a modern, condensing, boiler?
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On Sat, 18 Mar 2017 18:36:51 +0000, snipped-for-privacy@thanks.com wrote:

Do they make condensing oil-fired boilers now? AIUI they used not to, as the benefits in terms of improve efficiency were marginal (oil, having a composition with less hydrogen and more carbon than gas, per molecule or per unit weight, doesn't generate as much water vapour when burnt, so the energy to be recovered by condensing that vapour is less).
But there may be other benefits in a new boiler, especially if you have mains gas available and install a condensing gas boiler. If no mains gas, you could always install an LPG boiler but that would mean a gas tank in the garden and an expensive gas supply relative to mains gas.
--

Chris

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On 18/03/2017 19:00, Chris Hogg wrote:

I suspect you would find it difficult to buy a domestic non condensing oil boiler. Are you aware of any?
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Michael Chare

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On Sat, 18 Mar 2017 20:07:49 +0000, Michael Chare

Mistral make both apparently, https://www.mistralboilers.com/ but the situation has obviously changed since I formed the opinion expressed above. According to WHICH*, "Typically, a new condensing oil-fired boiler will have an efficiency of 92% to 93%, compared with 85% for a new non-condensing boiler and 60% to 70% for older systems." So it would be worth the OP's while to replace it anyway if it's an older boiler, even if he doesn't get a condensing one. * http://www.which.co.uk/reviews/boilers/article/oil-boilers
--

Chris

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wrote:

When we replaced our old Grant oil boiler with a new one (old one's heat exchanger rusted through) we were told that Grant no longer made a non-condensing one in the size that we needed. We've been pleased with the new boiler, though we get more "singing" from the radiators as the water-plus-Fernox is circulating - and that's with the pump turned to minimum speed. The increase in noise may be more due to the addition of Fernox (which may have loosened/dissolved deposits) than the change of boiler. The boiler itself is quieter (less of a thump when the burner initially lights up).
This is for an outside boiler, rather than a wall-mounted or under-worktop one in the kitchen etc.
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On 18/03/2017 22:01, NY wrote:

Interesting. How do you find having an external boiler? How does the condensate drain avoid freezing when the system is outside?
We may have to go down that route as the position of the old boiler is not suitable for fitting a replacement (basically it was put in place and an extension built around it).
No easy way to install a replacement upstairs without either knocking walls down or dismantling the boiler and reassembling it in situ.
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Martin Brown
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On 18/03/2017 20:07, Michael Chare wrote:

Big old cast iron oil boilers seem to be more reliable than the more modern ones which seem to be forever having electronics failures if my neighbours experiences are anything to go by.

I think you would also have to get special dispensation to fit one that wasn't condensing today. Alter it at all and you are supposed to comply with modern fire safety and bunded oil tank rules too.
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Martin Brown
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On 3/18/2017 3:00 PM, Chris Hogg wrote:

Yes, they do. We've had a Grant condensing oil-fired boiler for a few years now, and are very pleased with it. I don't have the figures to hand, but our oil usage has dropped considerably.

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On 18/03/2017 18:36, snipped-for-privacy@thanks.com wrote:

Is the boiler listed here:
http://www.homeheatingguide.co.uk/efficiency-tables.php?make=Mistral
You can also find the efficiency of new boilers.
Clearly the cost of installation will be less if DIY.
Then there there is the question of how much oil you will use, and you have to make assumptions about the price of heating oil.
FWIW I replaced my previous boiler with a new more efficient but non condensing one. I am sure that the boiler has paid for itself.
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Michael Chare

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On 18/03/2017 20:02, Michael Chare wrote:

That's an interesting link; I'll make a note of the model number when I'm next there.
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On 18/03/17 18:36, snipped-for-privacy@thanks.com wrote:

I moved last year. The oil-fired boiler here is 30 years old, regularly maintained by the same local man since installed. Parts are still available it may last a few years yet, whereas a new boiler may not last more than 10. It may only be 70% efficient but a new 95% efficient one is unlikely to shave more than £150 pa off my oil bill. So I plan to keep it until it breaks.
--
djc

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On 18/03/2017 18:36, snipped-for-privacy@thanks.com wrote:

After a bit of googling I think I can answer my own question. An efficiency improvement of 25% on 2000 litres/year (no idea whether that's correct) at 41p/litre is about £205, so that pays back at 15 years. If that's correct, and unless there are any grants, it's worth keeping the old boiler going for as long as reasonably possible.
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On Sunday, 19 March 2017 00:09:43 UTC, snipped-for-privacy@thanks.com wrote:

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It always struck me that one could improve the efficiency of old boilers by just turning down the gas or oil feed some, checking the exhaust stays at at least 120C so it doesn't condense (which would rot the exchanger). But I don't think such things are allowed.
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On 19/03/17 01:30, snipped-for-privacy@gmail.com wrote:

?
How can increasing the exhaust gas temperature increase efficiency? Surely that is just more heat wasted up the flue. It might prevent condensation, but at the expense of reducing efficiency.
--

Jeff

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On Sun, 19 Mar 2017 08:22:38 +0000, Jeff Layman

I don't think he's proposing to actually increase the exhaust temperature, the opposite in fact by turning down the oil feed rate, but avoiding it getting _too_ low and so allowing moisture to condense, resulting in corrosion of parts not intended to cope with hot and wet.
--

Chris

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On Sunday, 19 March 2017 08:22:41 UTC, Jeff Layman wrote:

you misread, I said pretty much the opposite
NT
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On 19/03/17 09:36, snipped-for-privacy@gmail.com wrote:

Agreed. I saw 2 + 2 = 5 (I should be in politics...)
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Jeff

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On Sun, 19 Mar 2017 15:15:49 +0000, Jeff Layman wrote:
====snip===

Or computer programming (2+2=5 #but only for large values of 2). :-)
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Johnny B Good

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On 19/03/2017 00:09, snipped-for-privacy@thanks.com wrote:

£3k for a boiler? Sounds a bit steep, or was that including commercial fitting as well?
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Cheers,

John.
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