Oil Boiler - best way to use

rosscouk

Hi there,

I moved into my end of terrace three bed room house about a year ago and I installed Grant 15/21 oil conventional boiler to run my eleven radiators (all with thermostats but all at maximum). Oil usage has been around 1700 litres with about 200 still in the tank from that. I am working on what I still need to insulate as the house is often far from warm.

In terms of the usage I have left the Grant at the output the plumber suggested, with the dial set to about a third of maximum power output. The thermostat for the house is in the hall but I had to move it closer to the transmitter (its wireless) as the signal kept dropping. Its currently set at 20.5 C although the house never really reaches that temp even if the heating is left on all day. We close the door next to the thermostat as the back of the house (two story extension) is quite cold and with the door closed the rest of the house is warmer.

So, my question, should I up the output of the boiler with the thinking being the house might reach the temperature quicker and it will then keep it there occasionally adding hot water to the system. Or should I leave it as it is although the boiler maybe on more trying to reach the unattainable temperature?

Obviously I am concerned with oil usage so I don't want to burn loads more. Whats the best approach?

Any help is greatly appreciated.

bernithebiker

I don't think it will make much difference. Sounds like the boiler is struggling to maintain room temperature anyway, so your consumption will be proportional to how warm you can get it in your house.

Having said that, boilers generally are at their most efficient when working at lower temperatures, so probably best to keep it on all the time at a medium level.

Obviously insulation is key. Then go for some kind of wood burner.

malc_b

Oil boilers are either on or off so if you set the water temperature on the boiler below max then all that happens is the boiler cuts out when the thermostat demands heat. Also, radiators output more the hotter they are. And the worst way to run an oil boiler is have it short cycle as you lose a bit of oil at each firing.

Of course, how well or poor the house is insulated will govern the amount of energy you need to put into the house for a comfortable temperature. By setting the boiler temperature to max you'll improve the burn time and so raise the efficiency and with hotter rads you'll provide the power the house needs. But if you want to save real money insulation is the way to go.

bernithebiker is thinking of condensing boilers when he says "boilers generally are at their most efficient when working at lower temperatures" which you say you don't have. Unless the water temperature is low condensing doesn't happen which I guess could be an 8% loss (best non con is 85%, best con is 93%).

Cardew

malc_b wrote: »

bernithebiker is thinking of condensing boilers when he says "boilers generally are at their most efficient when working at lower temperatures" which you say you don't have. Unless the water temperature is low condensing doesn't happen which I guess could be an 8% loss (best non con is 85%, best con is 93%).

I don't think the OP has made that statement. What he wrote was:

moved into my end of terrace three bed room house about a year ago and I installed Grant 15/21 oil conventional boiler to run my eleven radiators (

A boiler installed a year ago in a 3 bed terrace would almost certainly be condensing. I suspect by 'conventional boiler' he means it isn't a combi boiler??

http://www.discountedheating.co.uk/shop/acatalog/Grant_Vortex_15_21_Oil_Condensing_Utility_Boiler.html

smallblueplanet

malc_b wrote: »

Oil boilers are either on or off so if you set the water temperature on the boiler below max then all that happens is the boiler cuts out when the thermostat demands heat. Also, radiators output more the hotter they are. And the worst way to run an oil boiler is have it short cycle as you lose a bit of oil at each firing...

Do you actually have something to back this up with or is it just your guess? I ask because quoting efficiency stats for boilers of such high figures makes me wonder, I remain to be convinced that such figures are accurate rather than 'manufacturers figures'.

rosscouk

Thanks for the replies.

No it is not a combi boiler as I have a hot water tank and I understand it is a condensing boiler and I was told that most are now.

I also checked to see what the output of the boiler was set to, there is knob marked "Heating Temperature" and it looks to be set about 1/3 of the way around. I recall my plumber saying that this is the most efficient. As I didn't want to 'loose' the setting I have been running on all year I put a pencil mark at 12pm on the dial (inline with a marker on the boiler) and then tried turning it down. To my surprise the knob will not turn down and therefore I assume the knob is set to minimum 'Heating Temperature'. If I try and push it up to maximum, it only turns about 1/4 turn. With the knob on maximum it only pushes my pencil line to about 2pm. So not much play at all.

In terms of how the boiler runs when on, it does turn on, runs for a few minutes and then turns off, repeating this cycle whilst on, although it never reaches the 20.5c set in the hall. In fact that's probably too hot so have just move down to 19c, as when it hits 19c (when not too cold and left on for longer periods) the house is quite warm then.

So basically, would I burn more oil if i turned up the boiler or would I be burning less as the house would reach temperature sooner and therefore the boiler would turn off more quickly? Obviously I could test, but there are lots of variables.

malc_b

Yes, I assumed conventional boiler meant not condensing but I should have considered the age as well, my mistake.

With a condensing boiler you get better efficiency with lower water temperature, strictly lower return temperature so you always run in condensing mode during the first part of a burn, up until the radiators get hot.

Running for 2 minutes at a time is short cycling and not efficient. Setting a lower boiler thermostat means you short cycle but stay in the condensing range. I suppose that is better, you could ask the maker if it more efficient to go non condensing or to short cycle.

Do all your radiators warm up equally at the same time? You might want to try "balancing the radiators" (google that for instructions) to ensure that you are delivering maximum heat into the house. Balanced rads will mean you are taking max heat out of the input water so have the coolest return water and so stay condensing mode for longest.

The other question is how long you run the heating for? The heat loss of a house depends on the difference between inside and out, so say 20C inside to 0C outside. Now turn off the heating say overnight or during the day and inside temperatures falls to say 10C. So for the 8hrs you have CH off the average inside temperature is still 15C, the average loss is 75% of that with the heating on. That heat has to come from somewhere, the fabric of the house. That debt has to be repaid when the CH heating is switched on meaning it has to work harder. Running 16/24 reduces the cost to 85-95%.

Typically a CH system is designed to work to a -1C outside, running 24hr. The only allowance for the heat debt is the fact that you pick the next size up rads, next size up boiler, and the outside temp being above -1C. So in winter you need to run longer hours to keep the house warm.

malc_b

smallblueplanet wrote: »

Do you actually have something to back this up with or is it just your guess? I ask because quoting efficiency stats for boilers of such high figures makes me wonder, I remain to be convinced that such figures are accurate rather than 'manufacturers figures'.

Which figures? Radiators are specified at 60C above ambient, so 80C for a 20C room which is 85C water in 75C water out in round numbers (used to be 20F so 12C is usual figure now). For water at 50C the radiator output is about 50%.

Boiler efficiency figures are from sedbuk. Short cycling is said to be inefficient because the oil pump runs then the spark occurs so you lose some unburnt oil at the start and while the flame establishes itself. I've no figure for how much that is. My CH controller has an oil boiler mode with a 15min cycle, i.e. for 50% power it burns 7.5min every 15min, so it is a known effect.

rosscouk

I have just pushed the boiler output up to half way - we will see what happens.

Cardew

rosscouk wrote: »

I have just pushed the boiler output up to half way - we will see what happens.

Yes your Grant 15/21 is a condensing boiler.

The aim of condensing boilers is to get them operating as much as possible in condensing mode where their efficiency is higher. That, as stated above, is by having a lower return water temperature. See:

http://www.plumberparts.co.uk/how-condensing-boilers-work/



You say that the house temperature never reaches 20.5C with the water temperature recommended by the plumber set on your boiler.

In that case you need to raise the water temperature on your boiler - or get bigger radiators;)

The other important factor is that the output of the boiler modulates. i.e. it turns the output up or down as required.

rosscouk

again, thanks for all replies.

I have just been in the kitchen and timed what the boiler was doing. It seems to run in 3 minutes cycles with 1.45mins on and 1.15 mins off. Temperature has gone up to 17c at the thermostat since turning boiler up with radiators definitely hotter to the touch.