Worth replacing an old oil boiler?

[nospam]

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?

[Chris Hogg]

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.

[Michael Chare]

Is the boiler listed here:

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.

[Michael Chare]

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

[S Viemeister]

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.

[Chris Hogg]

Mistral make both apparently,

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.

[Andy Burns]

To be allowed to fit a domestic non-condensing boiler, you must pass an assessment procedure ...

[NY]

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.

[DJC]

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.

[nospam]

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.

[tabbypurr]

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.

[John Rumm]

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

[harry]

You need to check the oil tank as well. See if there is water in the bottom (there's usually a drain tap ofr this purpose). If it's a Steel tank there may be corrosion.

[Jeff Layman]

?

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.

[The Natural Philosopher]

Not nearly as much as getting the insulation sorted.

Boiler should be the last thing you tackle.

[The Natural Philosopher]

If its a non insulated house you can double the oil consumption tho.

[Chris Hogg]

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.

[tabbypurr]

you misread, I said pretty much the opposite

NT

[nospam]

It was only a SWAG based on: a boiler cost of around £2200, labour needed (these boilers are surprisingly heavy - around 270kg!) and replacing some pipework at the same time. Because immediate boiler replacement isn't obviously worthwhile I think we'll plan to live there and see what the actual oil consumption is. There are two wood burners (and I plan to open-up a third, currently closed) fireplace so their use is going to make a big difference to oil demand.

(In case you don't know, SWAG is Scientific Wild-Arsed Guess. I've always liked the term and have used it most of my professional life ;-) )

[nospam]

The window frames are steel, mostly single-glazed but some have been double-glazed. One of the early tasks will be tidying-up the windows and looking for ways to fit (thin) double glazing panels to them - expect another thread on this once we've moved-in!

Apart from windows and doors I don't think there's much scope to improve the insulation, but I'll certainly be investigating what can be done. The construction appears to be rendered concrete block but I don't know yet whether there's a cavity. The loft is large (purlins, so no obstructions), high, fully boarded and with boards on the outside of the rafters (Sarking boards?). Lifting the floorboards would be a helluva job and adding decent insulation between the rafters would be very expensive.