View Full Version : Info needed re oil fired boilers

14th Jan 2009, 11:47
Greetings one and all,
I never tire of the vast array of knowledge displayed here and now turn to you all for advice / hints / tips etc for buying a new oil fired boiler.
The current one is starting to "play up" and is nearly 14 yrs old.
I have to say that if I was starting from scratch, oil wouldnt be my fuel of choice - but I'm afraid that the current infrastructure is set up for it - so (for now) - it stays.
So what should I look for? - what should I be asking? - whats the latest in this field?
I need it for hot water and Central heating.

14th Jan 2009, 13:03
Having gone through the flail about 18 months ago as this house was being built.
1. Condensing or coventional? Condensing uses less fuel but is more expensive, efficiency about 90 and a bit%. My current Boulter conventional came out if it's last service before Christmas at 87%. Is the price differential worth the more expensive option.
2. Inside or outside? Outside (in an insulated box) gives more room in the house but efficiency drops a bit (According to the Energy Saving Trust). Inside can warm your airing cupboard, the circulating pumps generate noise (not a lot but you'll be aware of them).
3. "Sizing" the boiler is critical. Most plumbers will say "x radiators, hot water,towels... um call it Y kilowatts". This might be bigger or smaller than you need. Do some research, measure your room sizes, check insulation levels, double glazing? then you can have a better idea of what you need. There are on-line calculators to help. Plumbers work on the basis of assymetric information and won't tell you what's best for YOU.
The Ancient Mariner

Rather be Gardening
14th Jan 2009, 14:38

We're going through the same process. Present boiler is a Worcester Heatslave 20/25, about 12 years old, and has had to have the water tank and pump replaced these past 2 years. Looking at getting a condensing boiler, with solar hot water panels. The Grants brand comes out well in 'Which' surveys and was also recommended by the plumber who services the existing one. Here's a link:
Grant Engineering - Home | Efficient Heating Solutions (http://www.grantuk.com/)

14th Jan 2009, 14:45
My daughter lives in Cornwall and they have oil fired heating
and hot water.
During the recent cold weather the heating went t*ts-up due
to the fact that they live in a house some 100yds away from
the oil storage tank. Which is situated near a small lane.
The pipe that delivers the oil to the heating unit froze solid
and no oil was delivered to the heater. Despite the pipe being
really well lagged.
Just managed to survive using the wood-burner in the lounge
and the electricery.

14th Jan 2009, 15:08

If you have the capital and the roof space/location, now could be a good time to look at installing a couple of solar water heating panels - you might find you get quite a good payback, and rarely need to use the boiler in summer. Plumbing them in as you get a new boiler would make a lot of sense. They won't help in winter to any extent, so you'll still need the same max output from the boiler.

And join me in praying that the oil price stays low - my last deliver was 37.5p/litre, a massive fall from 52p.

14th Jan 2009, 15:29
We have oil heating too. We don't have a choice of gas as we are living in woodland and very rural. Our boiler is at least 25 yrs old, it's serviced each year and has worked ok until...

...our boiler decided to die on us on 30 Dec! However, the problem wasn't the boiler itself, but the filter in the oil tank.

The filter of the oil tank (where the oil passes through before it leaves the tank to run through the pipes to the boiler) can become contaminated with water over time, and in very cold weather, this water freezes thus cutting off the oil supply to the boiler.

The heating engineer who came out on the 2nd Jan did a thorough test of the oil tank, and thankfully the oil was fine, it was just the filter. He cleared it all out of the debris that had collected, as well as the ice, performed a full service on the boiler, and now our boiler is running at 3% more efficiency than it was prior to the problem. It also 'sounds' much smoother too.

So, it may be a good idea to periodically check the filter in the oil tank - it appears to be a problem experienced by others too, as a couple of days later, exactly the same thing happened to the boiler of someone I know!

btw, the last delivery was in Nov, and cost 45ppl.

Hope this helps.

14th Jan 2009, 15:36
...... and now our boiler is running at 3% more efficiency than it was prior to the problem.

How do you work out boiler efficiency :confused:

Windy Militant
14th Jan 2009, 15:42
3. "Sizing" the boiler is critical.
Interesting point raised during the recent cold snap. My mums house built god knows when, with three foot thick stone walls, oil fired boiler added in place of solid fuel burner about ten years ago, nice and toastie boiler running about capacity.
Brothers house built 1980's, boiler running flat out house bearable temperature.
Nephews house built circa 2003, heating flat out, house cold.
Nephews house was built by a housing association so probably built down to a price, so the boiler installation and insulation was minimum allowable under building regs, which was fine over the last few mild winters but not sufficent for the sustained cold weather we had over the last month or so.
So a little overcapacity may not be a bad thing! ;)

14th Jan 2009, 16:08
Quote: How do you work out boiler efficiency http://static.pprune.org/images/smilies/confused.gif

I've no idea! The Heating Engineer did it for us! Efficiency is running at 86%, as opposed to 83% prior to the problem we had, and admitedly a good service. We have a Trianco.

Here is a good website, that shows the efficiency of boilers, with a good search tool.

14th Jan 2009, 16:10
Thanks to all for answers so far!

AA - Already installed the solar panels - Brand new system installed last spring - evacuated tubes, mega tank in loft and very nice fuzzy feeling in very sunny (yes even in winter) weather when the hot water is coming warmed by the sun.
Next project to put either photovoltaic cells on workshop to power that- Might even go for a small turbine to top up battery bank! planning permission is no longer needed for small (domestic) turbines!:ok:
Its just that our current boiler is starting to show its age and is not V reliable.

Any more help and pointers most welcome.

14th Jan 2009, 16:27
Ideas? Heres one. Particularly effective with a non-condensing and highly reliable boiler which I dont want to get rid of. The new fangled ones break down every other week.

Parts List.
1. Old Turbo heat exchanger from scrappy.
2. Bits of pipe.
3. Pretty grill inside - to keep wife happy.
4. Old fan from boiler.
5 Thermostat/Fan ON-OFF.

Put em together and what have you got. Heaps of hot, 120C FRESH AIR coming into the house - for nowt (apart from a bit of electricity.) Not perfect, but Im a cheapskate. :)


14th Jan 2009, 17:31

Not an attack; would you like to send us a diagram of how that system works. Viz;what heats the air and how do you duct it around the house?
The Ancient Mariner

14th Jan 2009, 21:16
Not an attack; would you like to send us a diagram of how that system works.

Attack! What mean this. :confused: Anyway, I put the thing together in a fit of boredom a couple of years ago. You asked for a diagram and, incredibly, with a bit of searching, I have one. Bear in mind, boredom and shed were the key words.


14th Jan 2009, 21:34
Another option is a Ground Source Heat Pump but I think that it takes a few years to get pay back.

Ground source heat pumps - Heat pumps & ground loops - Energy Saving Trust (http://www.energysavingtrust.org.uk/Generate-your-own-energy/Types-of-renewables/Ground-source-heat-pumps)

14th Jan 2009, 21:35
Wow!!!! Or should I say " Oh [email protected]"! Only today I said to SWAMBO (She Who Always Must Be Obeyed) - "If only we could tap all this hot air coming out of the wall!!!!"... The prob bieng- she knows I have posted this on PPrune and will prolly check out the answers.... Ok - Its off to the scrappy in the morn. Thanks mate...

Seriously- What a brill idea.:ok:

14th Jan 2009, 21:41
Saintsman- Thanks for that. I have looked into this option but really only viable on a new build project, ie before the house is built on top of the unit, (unless one has acres of land surrounding ones estate!!:8)

14th Jan 2009, 22:28
Quote: How do you work out boiler efficiency http://static.pprune.org/images/smilies/confused.gif

The last time we had our oil fired boiler serviced the engineer talked me through everything he was doing, and showed me how the efficiency is measured. He used an special electronic thermometer - the probe was placed into the flue through an aperture inside the boiler. This measured the exhaust gas temperature which was (somehow) converted to a digital efficency reading by the thermometer...the efficency was taken when the reading stabilised. I think ours was 86%, not bad for a million year old boiler.

The colder the exhaust gases going out of the flue the more efficent, as this means the heat being generated isn't going straight outside..

14th Jan 2009, 23:41

So often in Pprune a simple question seems to generate "defensive" aggro, it was an attempt to defuse that. However, another question, where do you take the warmed air to? In the commercial versions of your system there is usually a set of ducts and ceiling vents to take the air to each room. I take it yours is a simpler and cheaper approach. No?

Ta for the diagram. I spent some time after my earlier p**t and had more or less worked it out. Is the fan timed into the boiler firing?
The Ancient Mariner

14th Jan 2009, 23:59
I don't know for sure if it applies to oil, but you're no longer allowed to fit a non-condensing gas boiler in the UK. I think it's the same for oil. The oil boiler in our Norfolk hideaway is condensing - but that was there when we bought the place.

They don't last as long (all that acidic condensation eats up the innards). I doubt if the extra efficiency of the condensing bit offsets the cost of making a whole new boiler every 8 or so years. Our old gas boiler here (non-condensing) is over 30 and still going strong. Long may it continue...

15th Jan 2009, 00:09

mini haus converted to a condensing oil (kerosene) boiler last year, very straightforward, half day job.

Heating bill has halved.

Investment recovery was initially two years, with the sudden decrease in oil prices it will be longer but still 40%+ reduction in consumption vs 30 yr old boiler with 2 yr old burner.

Downside is a condensate plume that can be embarrassing if you live in close quarters to your neighbours...

Scumbag O'Riley
15th Jan 2009, 06:59
One hates to question forget's excellent idea, but that heat exchanger must modify the airflow out of the flue, and one wonders if that causes some sort of 'backpressure' which can interfere with the boiiler. I realise there is probably a fan in there pushing the products of combustion out, but from bitter experience of boiler malfunctions due to incompentent CORGI engineers, messing with the flue can have negative consequences.

15th Jan 2009, 08:17
There is only one proper way to work out the size of boiler you need and that is to calculate the heat loss from the outside walls and roof of your house. I did this using info from a company called, I think, Sherborne heating, (or maybe Shelborne) in the UK for five apartments I converted.

When I got to Canada and was building a house the locals wanted to do their usual "Oh, it is x square feet so you want Y BTU." I used the old details I had and did a heat loss calculation. We had the house for ten years with a condensing gas hot air furnace. When the furnace fan needed the bearings reoiled I stripped it easily and it was mint clean. The local engineer had never seen a clean one before, even after a year. Apparently things are usually so gunged after a couple of years they do not even sell the exhaust fan by itself because it can not be split without breaking it up. The point is the local, "BIG is big enough" causes the furnace to cycle too often so acid condensate forms too often and does not get blown or evaporated out. IT is important not to oversize the furnace.

Take the heat loss at your coldest expected outdoor temperature and add only 10% (as the furnace must raise the temperature from overnight setback to be comfortable when you get up in the morning,) Size your furnace accordingly. It is not difficult. The first time I did it Excel had not even been invented! (Now it would take about ten minutes.)

A small aside on heat recovery as shown. It is simple and probably effective if you use a non condensing furnace, however I would suggest a cast Iron section of flue through the H exchanger or VERY regular inspection as, like the heat exchanger on a GA plane, any perforation of the metal there opens the inhabitants to possibility of carbon monoxide poisoning. Same of course for the heat exchanger in the actual furnace.

Mostly modern furnaces must have the intake and flue balanced against the exhaust fan though it is particularly important on condensing furnaces. On the one we had installed the actual commissioning had to be done by a registered installer to get the warranty and he measured the temperature of the exhaust, the flame in the chamber and the heat gain across the furnace heat exchanger.

15th Jan 2009, 09:24
However, another question, where do you take the warmed air to?

To keep things (very) simple the hot air is pushed through a vent in the utility room ceiling and directed through the door to the kitchen. Where it goes after that is anyones guess.

Is the fan timed into the boiler firing?

No, the boiler and wiring are completely unchanged. The new thermostat is simply attached externally to the boiler casing. When the boiler fires the casing warms up and eventually trips the fan thermo. By then, the heat exchanger matrix is hot. When the boiler switches off the fan continues until the casing has cooled down. The thermo is set for this to coincide with the heated air coming in dropping to about 70F.

Scumbag, that heat exchanger must modify the airflow out of the flue.

The boiler is fitted with a very sensitive pressure differential switch. If airflow through the boiler and flue is out of spec the boiler wont fire.

15th Jan 2009, 10:10
This as discussed is caused by free water freezing in the bottom of the fuel tank. To keep this water out of the fuel line your tank should be inclined away from the fuel outlet pipe so that the water collects at the low point on the other end of the tank. (it should have been installed this way) At this end of the tank there should be a valve which allows you to drain this water off occasionally. (I used to check it after every fill.) If there is no valve then there will be a plug which you can remove and when the level is low and fit a valve. If your tank is not inclined then you should incline it by jacking up the oil outlet end (use a wooden batton or the jack will burst the tank) Then fit a 4 cm spacer between the tank base and the main support and set tank back down on the support. If your tank is inclined and you are still getting water in the oil outlet line then your oil supplier should be contacted as you oil is water contaminated. If you are being supplied by road tanker ask the driver to blow the hose after pumping to ensure what was metered to you actually arrived in the tank He does this with exhaust gas from his engine. (Check what you received by marking the level on the tank gauge glass before and after delivery and check against the meter ticket, there have been fiddles in the past.)
The "efficiency test" by sampling the flue gas is an oxygen check to check the burner combustion efficiency. ( it is not a central heating system efficiency) If you are burning oil this will be poor if the atomising tip on the burner is in poor condition. These are easily damaged by the cutting action of the oil passing throught the brass tip and are the main reason for poor combustion. The tips are easy to change and cost about a fiver. I used to change mine every three months.
If your boiler has a vertical flue, then you can buy an economiser, which replaces the first length of flue pipe (it is the same size and has the same screwed connections) When fitted,the water returning to the boiler from your Central heating system, is piped through the economiser first before entering the boiler and is therefore preheated by the boiler exhaust gases. With a clean burner tip and an economiser your oil consumption should fall by approx 30%. You will find the economisers on the net.

15th Jan 2009, 10:50
Oilandgasman! :uhoh: That's blown it! We've got a pro on the thread. ;)

... is piped through the economiser first before entering the boiler and is therefore preheated by the boiler exhaust gases.

I had something similar in mind to pre-heat the intake air but, although I never got around to it, I still think it would make a big difference to s. Biggest advantage is that gains are made all year round for hot water/heating, rather than just hot air in winter.


cockney steve
15th Jan 2009, 13:54
Forget.....I thought of that, too, but it is FLAWED LOGIC
hot air is less dense, therefore, for a clean, efficient burn, you have to reduce the fuel or increase the air.

The air supply quantity is CRUCIAL! We've already heard in previous posts, about acid flue gases. too much airflow will also pull heat up the chimney....too little and condensate will eat away the flue and the boiler.

I had many fascinating conversations with a retired power-station engineer friend,who was the "top dog" on shift, -he ran coal, oil and Nuclear...can't remember if we discussed gas, but he knew all the stuff about the boiler we were recommissioning.

To the thread-starter.... As Keef and others have pointed out, you need a lot of fuel-saving to recoup the cost of a new installation....this is another government con!

New , high efficiency boiler......" well, guv. it's pressurised and your old radiators and pipes won't take it".....so a complete installation.

Old oil-boiler....on the commercial sizes, AFAIK, completeburner/controller modules can be slotted into a standard hole....the boiler itself being just a big jacket wrapped round the flames to collect the heat.

Yes, eventually it will rust/burn /erode and leak....but until it does, the "wearing" bits can be replaced.......also, bear in mind, some of the new boilers are sealed, throwaway units

A friend installed a new one Ravenheat?...not sure, but it was over a year before it was commissioned, so warranty out......6 weeks, wire shorted to casing/coverplate....new circuit -board, 150 or -so.

another 2 months ...gas valve US...."about 180 guv." just for part....so he consulted with a "man in the trade" binned the boiler, substituted a Worcester-Bosch, which was RATED at 5,000 BTU more.

the difference was astounding! approx 50% quicker to warm the house and the lukewarm shower has been transformed , he can't turn the dial above 2/3 now!

Anyone should beware and do a LOT of research ....otherwise you are liable to buy a "pup"...Yes! even well-known and advertised brands,

edit:- forgot to say, you can get heating-tape to go along the underground pipe, unfortunately it needs electrickery but your oil will never "wax"

15th Jan 2009, 14:05
Forget.....I thought of that, too, but it is FLAWED LOGIC.

Oh no it ain't.

A furnace, oven, or boiler will consume less energy when supplied with preheated air. Boiler efficiency typically improves 1% with each 40F rise in intake air temperature.

IAC - (http://www.ceere.org/iac/assessment%20tool/ARC2411.html)

If you need diagrams or parts for your boiler this is a gold mine. :ok::ok:

PartsArena (http://www.partsarena.com/baxi/)

PS. Come to think of it, the 1% with each 40F rise in intake air temperature is probably the reason I didn't bother. :hmm:

15th Jan 2009, 18:55
Why don't you run the boiler at the regular temperature and use a simple heat exchanger and a second circuit to heat the extension floor?

Running the boiler at a "non design" temperature seems like an invitation to future problems.
The floor heating temp should be down close to the actual room temp of the floor or it will be uncomfortable and may cause ankle swelling etc.
If the floor is concrete running the temp higher may cause cracking.

A simple thermostat controlled pump and secondary circuit via a heat exchanger sized to heat the floor only to (say) 23C and controlling a simple motorised valve to cut off the H/E which is in parallel to the radiators would do it at very little cost.

16th Jan 2009, 10:13
Agree all that ChrisVJ states drop me a PM if you wish. It might be cheaper and simpler to go for rads in the extension. As you are on propane I suspect you are out in the sticks a tad and mains gas is not an option.

16th Jan 2009, 20:02
Looks like a very neat job forget, but I'd be very surprised indeed if this type of home made modification was legal under the gas regs in the UK, particularly a modification which affects the flue....

Loose rivets
16th Jan 2009, 20:46
Just astonished at the money folk spend these days. Bro had a condensing thing, fat end of a grand it cost. Slung it out in a very few years. So two hi-tec thingies, how will he ever recoup that? Oh, and he had numerous breakdowns cos of PCBs failing.

My house had an oil burner when I moved in. My mate that owned the house got his oil billed to his company. It owned the house BTW. 500 galls, 35 quid. That's not a mistake. I got the same deal...I'm not kidding with this, by telling them I was a...cringe, can't believe I did it...by telling them I was a pilot.:rolleyes: 'We buy thousands of tonnes of fuel' I told them. LOL I even got green shield stamps! Yards of them.

I converted to gas and got Big Bessie that I mentioned in the Best bargain type thread the other day. 60 quid, and so powerful. Cleaned it out twice in twenty five years. Oh, and changed the thermocouple for a generic one. I put a modern system in to sell the house. It was cr*p. and saved about twenty %...all by keeping the house freezing I would think.

16th Jan 2009, 21:04
....... but I'd be very surprised indeed if this type of home made modification was legal under the gas regs in the UK, particularly a modification which affects the flue....

Blues, Purely out of interest, a friend of a friend, industrial Health and Safety inspector, came to look at it. He didn't have a problem. The pressure differential switch was good enough to know the flue was happy, and a perforated matrix means fresh air into the exhaust - not the other way round.

Scumbag O'Riley
16th Jan 2009, 21:40
My understanding of these things (gained by myself as I watched CORGI engineers not have a clue how to fix my buggered boiler) is that the pressure switch is a check to make sure the fan is running, not that the flue is OK.

In fact with my boiler the flue was the problem and was causing the pressure switches to fail, but only every six months.

16th Jan 2009, 21:48
pressure switch is a check to make sure the fan is running, not that the flue is OK.

It's smarter than that. It measures the pressure diff between two points, which is dependent on airflow, which is dependent on the flue being clear.

Scumbag O'Riley
16th Jan 2009, 22:10
Not wanting to dismantle my boiler :) but ....... from memory ...... it measures the pressure at a venturi in close proximity to the fan. So it only says the fan is blowing air. It doesn't say where that air is eventually going. It could be coming back into the boiler housing, and then out into the room.

That was the problem with my boiler, the products of combustion were coming back into the boiler housing and frying the components, but not quickly enough to fail while the engineer was there.

Boiler fails. Diagnostics point to pressure switch. CORGI changes pressure switch. Works. CORGI thinks its fixed, invoice.

Boiler fails. Diagnostics point to pressure switch. CORGI changes pressure switch. Works. CORGI thinks its fixed, invoice.

Boiler fails. Diagnostics point to pressure switch. CORGI changes pressure switch. Works. CORGI thinks its fixed, invoice.

Whereas all along the flue was incorrectly installed, and was frying the pressure switch.

But only slowly :)

16th Jan 2009, 22:20
I'll have a natter with my dad. He's a CORGI registered gas installer, see what he says.

The installation may well be perfectly safe operationally (i.e. no significant flue obstruction) but I don't imagine the regs will allow for any non-authorised modifications to any part of the installation, as this would be carte blanche for anyone at all to do all sorts of dodgy stuff with btheir boilers!

EDIT: Sorry forget, quote on viewing photos "...should be classed as ID, immediately dangerous,there should never never never ever be any restriction on flue gases,POC,products of combustion,whether from a powered fan or not."

Also asked if the system had been submitted to CORGI for approval.


11th Jan 2012, 23:15
Holy thread resurrection, Jet Blasters! I have a question about my oil fired hot water and central heating system. We moved into an old house (renting) with oil fired HW/CH about 4 months ago. Never been oil fired before.
CH seemed a bit crap do the system has been chemical flushed. Slightly better but some rads do not get as warm as others. Had the boiler checked out today and it seems to be tip top: CO and CO2 well within limits and running at 93% according to the bloke's probe in the flu.
We have used about 500 litres of keep in the last 2 months running the CH a couple of hours in the morning and 3 in the evening. HW is on an hour in the morning and evening. Even so, it is clearly much more expensive than gas fired.
My question is what is the most efficient way to set this up? Should I leave it on and run it on the thermostat to keep the water tank warm as the engineer proposed? Or do I suck it up and use just the immersion heater in the summer to defray the cost?

12th Jan 2012, 01:54
No, Know anything about parachutes?

12th Jan 2012, 23:22
I do. Or rather, I did. I have not jumped for ages.

13th Jan 2012, 15:56
I had the water trap freeze last year when it was -11.5 deg C. Used a hot air gun to unfreeze it, but all the cold oil froze it again in 20 minutes. Hot air gun again, wrap the water trap in roof lagging with a 22 ohm 25 watt wirewound resistor included, and two wires into the laundry where the boiler is. 12 volts from a lab power supply and no more trouble.

Worst part was the snow dropping down my neck as I installed the lagging.

13th Jan 2012, 16:20
I use oil fired CH/HW and for the CH it is on the whole time from around November until April and is controlled by a main thermostat, with thermostatic valves on individual radiators in the conservatory. The HW comes on twice a day for an hour each time.
You don't say how big a house you're heating but mine is 1400 square feet and I'm running eight radiators. You seem to be burning a lot of oil. Coincidentally I just bought 800 litres this morning but I last filled my 1100 litre tank last April.

B Fraser
13th Jan 2012, 19:33
I'm in the process of buying a new place which is about 3200 square feet with high ceilings. Not owning my own oilfield (although see the devolution thread), I am considering a wood pellet combi boiler to replace the oil burner supplying the house from an outbuilding. The downstairs rooms will have log burners installed. I know a bit about log burners however does anyone have any experience with wood pellet systems driving hot water and radiators ? I'm opting for this type as there's little control over moisture content with wood chips and I can get resupplies of wood pellets blown into a silo in an adjoining shed.

13th Jan 2012, 21:05
Beaufort1 Don't know the square footage but it is an ok sized 4 bed detached with 12 rads.