Oil Boiler - best way to use

Cardew

malc_b wrote: »

That's not good for efficiency as you waste oil at each start and stop.

I don't know as I don't have any figures for the loss due to short cycling.

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Likewise I have not seen any figures 'for the loss due to short cycling'

However the comment by the Director of Worcester is interesting;

we don’t see any great difference in efficiency between an on/off burner and a modulating burner.

However, as you say, he is arguing strongly that 7% is not representative.

malc_b

Cardew wrote: »

Likewise I have not seen any figures 'for the loss due to short cycling'

However the comment by the Director of Worcester is interesting;

However, as you say, he is arguing strongly that 7% is not representative.

There are so many variables.

First off, there is no difference if you don't have oil condensing boiler, do have the boiler set to max, and do have a smart controller. In that set up you get almost no short cycles so there is no difference between modulating and not.

So only oil condensing boiler is of interest and then, assuming you set boiler thermostat to max any difference depends on how long you are in non condensing mode. That depends on how big your radiators are, their age, and probably how smart the controller is (and how you have it set).

The reason radiator size affects is of course it govern how hot they need to be to output the power the house needs. Their age will affect how much water is in the system as older radiators held more water. More water means the boiler burns longer in condensing mode heating the water up so more water makes it more efficient. I think. The most efficient is keeping the radiators at a constant temperature just high enough to give the power required, say 50C. Inefficient would be heating the rads up really hot then letting them go really cold, say 80C down to 20C so average 50C. So have a lot of water in the system would help.

Likewise how the controller runs the CH could also affect things. It's hard to see how you come up with a figure for modulating vs on/off without making a whole lot of assumption about the CH system which are likely not to be true for many houses.

rosscouk

I just re-read the thread and I am not sure I understand it all although that's likely to be me!!

Essentially I understand that if I have the boiler output low (minimum in my case) the return water for the CH will be a lower temperature and therefore two things are likely to happen; the boiler will be short cycling (which is bad for oil economy) although the boiler will be able to condense because of the lower temperature, so there may be a saving there. If I put the output of the boiler up (half way for me currently) I am likely to burn more oil to get it to temperature but when it is there (currently set to 18c in my hall) the boiler will generally be doing longer burns and this is more efficient however it will not necessarily be able to enter condensing mode as the return water is already reasonably hot.

There is no doubt the house feels warmer and generally more pleasant, however it remains to be seen how this higher output effects oil usage. Currently the boiler is set to come on for a hour or so in the mornings and four hours in the evening although generally it has been on alot more when we have been at home due to the weather, so its not a 'true' like for like test.

There are other measures to consider such as radiator size and insulation and the like. I am going to work my way around each room checking radiator size.

In the short term, I plan to change the drafty stable door in the kitchen and install one extra radiator to the kitchen. How would an additional radiator (going from 11 to 12) effect oil usage?

I then need to think about lowering the thermostatic rad valves a little in the bedrooms. If the house is warming faster it doesn't make sense to heat all the bedrooms as fully as the main rooms down stairs.

Somewhere in this is the ideal solution of oil usage, boiler settings, insulation, radiator settings, thermostat settings, radiator size and I am working towards that.

I am just wondering if I could lower the output of the boiler a bit and still get similar outcomes, it may just be a case of trying it.

Funnily enough, one day after going to higher output on the boiler my watchman has now gone to '1' telling me I am not far from needing a refill. I have used about 800 litres since the beginning of October.

malc_b

rosscouk wrote: »

I just re-read the thread and I am not sure I understand it all although that's likely to be me!!

Essentially I understand that if I have the boiler output low (minimum in my case) the return water for the CH will be a lower temperature and therefore two things are likely to happen; the boiler will be short cycling (which is bad for oil economy) although the boiler will be able to condense because of the lower temperature, so there may be a saving there. If I put the output of the boiler up (half way for me currently) I am likely to burn more oil to get it to temperature but when it is there (currently set to 18c in my hall) the boiler will generally be doing longer burns and this is more efficient however it will not necessarily be able to enter condensing mode as the return water is already reasonably hot.

Yes, that's physics for you.

rosscouk wrote: »

There is no doubt the house feels warmer and generally more pleasant, however it remains to be seen how this higher output effects oil usage. Currently the boiler is set to come on for a hour or so in the mornings and four hours in the evening although generally it has been on alot more when we have been at home due to the weather, so its not a 'true' like for like test.

There are other measures to consider such as radiator size and insulation and the like. I am going to work my way around each room checking radiator size.

In the short term, I plan to change the drafty stable door in the kitchen and install one extra radiator to the kitchen. How would an additional radiator (going from 11 to 12) effect oil usage?

Instead of number of radiators think of house heat loss. If your CH heat maintains the room design temperatures then doubling the number of radiators will not change oil usage. The oil you burn heats the house so if it stays at the same temperature then the amount you use is the same. However, with a condensing boiler, more radiators means lower water temperature so longer in condensing mode (or being in condensing mode later in the heating season).

That said most people add radiators because a room is too cold so if the new radiator raises the room temperature (to be more comfortable) then that will increase oil usage of course.

rosscouk wrote: »

I then need to think about lowering the thermostatic rad valves a little in the bedrooms. If the house is warming faster it doesn't make sense to heat all the bedrooms as fully as the main rooms down stairs.

Thermostatic valves will be full on until the room nears the set temperature then they'll turn down so if you have the bedroom set 21C but it only reaches 18C then it makes no difference if you set 18C on the valve. The radiator will still be full on when warming up the house in the morning.

If you find some radiators are hot while others are cool when warming up the house then you need to "balance the radiators" (google that) so they all have equal shares.

malc_b

It might be worth while if I post my house details and oil usage for comparison. I have a 1978 house with extensions so it a mix of brick/block, brick/celcon, solid floor slabs and insulated floor slabs. Last extension was 12 yr ago. Loft insulation is 270 and 150 (I think). It's a 5 bed in the south (near M4) and in a rural but not exposed location. Fully double glazed uPVC but mostly not to the latest (U=1) standard. Old walls have been cavity filled with polystyrene bits.

Calculated house loss is 7290 W for -1C outside. There are 16 rooms and 16 rads. Boiler is not condensing, oil fired, 12/15kW with a 15kW nozzle. Rads are 130% oversized in the main. Calculated degree days estimates a 2200 l pa. I reckon I use about 1500 l pa so the degree days is a bit out (or its the mild winters we've had recently). This year I'll probably use 1000 l as I now supplement the oil with E7 in early hours rather than use oil (convectors on time clocks). E7 is cheaper than oil, plus as I only have small oil tank it avoids a mid winter fill up. HW is also on E7 now rather than oil.

Silent_Dancer

In Winter turn the boiler heat output to full. The boiler needs to work harder to cover the heat loss from your house. Your heating system will be designed on the assumption of an 80C flow temperature the max setting on your boiler.

If you're still having problems after doing this there could be problems with sludge in the radiators, air in the system or a boiler fault.

In Spring and Autumn turn the heating dial this will reduce the flow temperature the boiler will condense more saving money. The lower temperature will improve the comfort of the home as the boiler does not overshoot.

ilikecookies

Very interesting thread indeed - with so many variables it's hard to know what's best. If I were starting from scratch I'd definitely be oversizing the radiators in the 50-75% range but for most of us we have to operate what we have and of course oversizing has a cost attached too!

Just speaking from experience I turn up the boiler stat up gradually as the temperature gets colder. In theory I accept this is less efficient as the boiler will probably not be condensing as much but it brings the house up to temperature much quicker. The alternative is to maintain the lower temperature but run the heating for MUCH longer which overall I think may use more oil because of the increased cycling. I'm not sure if we'll ever get to the bottom of which is the most efficient way to operate.

It's probably worth throwing another spanner in the works. My internal stat is a Honeywell DT90E which has a feature called TPI which I think is becoming increasingly common across all manufacturers. This aims to maintain a steady temperature and I can't fault its performance per se: for example when I set my stat to 19.5 degrees the stat is VERY efficient at maintaining this exact temperature slipping above or below very rarely. The downside is that it calls for heat VERY regularly to maintain this temperature. In theory this is more efficient than letting the temperature drop to say 18 before firing back up to reach the setpoint of 19.5 degrees. However a lot of folks report that they think this accuracy reduces efficiency as it leads to more, and shorter, firings (even firing above the setpoint as it anticipates the best operation). The settings can be adjusted (to set a maximum number of firings per hour, plus the length of the firings) but these stats do still fire more than traditional "less intelligent" stats.

At the end of the day it all seems like swings and roundabouts! When fuel/heating costs were lower I don't think we really thought too much about it but now costs are so much higher we perhaps over-analyze it!

ilikecookies

Also in specific reference to the OP - do you know what output (15kw, 18kw or 21kw) you're boiler is set too? I suspect it will be the middle setting as I think this tends to be the factory default. Getting a plumber to increase the output (which requires a nozzle change and pump pressure change) may also help you get up to temperature faster. Of course you'll use more oil though - catch 22!

Cardew

ilikecookies wrote: »

I'm not sure if we'll ever get to the bottom of which is the most efficient way to operate.

I think that sums it up perfectly.

Indeed even if you could find out the most efficient method of operation, most of us would probably sacrifice one or two percent of efficiency to have the CH more effective in it's primary role of providing comfortable heating.

Probably the most fuel efficient way to drive our cars is to not exceed 30mph in top gear;)

murphydog999

I found this thread a couple of days ago and looked at the thermostat dial on the non-condensing, at least 12 year old oil boiler we inherited. It was in what I would call an 8 o'clock position - pretty much off! - so I turned it to 1 o'clock and the difference in the house - as you would imagine - has radically changed.

The next morning I am awoken by a loud drumming/vibration noise from the ceiling below a water tank. I turned the heating off, it stopped, waited a few hours, turned it back on, about half an hour later it started again. I have turned the dial on the boiler to 12 o'clock and it hasn't happened since, but the house isn't as toasty - I was really enjoying this new heat as well!

I haven't been able to get hold of our usual plumber yet, so could anyone shed any light on what's happening? I'm thinking water got too hot - heating and water heating and tied in together for some reason???