Heating Oil Consumption

lohr500

Fair point also Reed_Richards.

I guess if the water hits the tank thermostat temperature well within the time setting window, then the only risk is that if the water  temperature drops by a few degrees during the remaining time, it could cause the boiler to fire up again for a short period to restore the tank temperature. That short burn time is possibly not very efficient as all the water in the pipework/boiler jacket will need heating up to operating temperature again. And if the boiler temperature cools down sufficiently whilst the water heating circuit is energised, it will fire up briefly, even if the tank thermostat is not calling for heat.

Probably doesn't make a lot of difference though and hopefully with a well insulated tank, the heat loss over 15 to 30 minutes should be minimal. It will also depend on the sensitivity and hysteresis loop of the tank and boiler thermostats as well. 

I think in my case, the bigger saving is determining when to use electricity and when to use the boiler, based on the relative costs of off-peak electricity and the price of oil.

When the bottom of our ancient jacket insulated immersion cylinder rotted through in February I had it replaced with a modern encapsulated insulation version which will also be helping to minimise heat loss from the cylinder.

Alfster

lohr500 said:

My gut feel says the tank thermostat setting shouldn't be higher than the boiler flow thermostat setting.
Otherwise the tank will never reach its set temperature and this will cause the boiler to cycle on and off frequently.

I run my boiler with a 60 C flow temperature and the tank set to 55 C. For a boiler to condense effectively (and so help with efficiency) the return water temperature needs to be below 54 C.  When our central heating is running, I am seeing a return temperature of between 45 and 50 C. The lower the return temperature below the magic 54 C, the more efficient the condensing process. Adjusting the flow and return temperatures involves playing around with the boiler thermostat setting, the circulation pump speed and the balancing valves on the radiators. It took me a while of trial and error to fine tune our system, but hopefully worth while to save on oil consumption. You can buy reasonable quality Brannan clip on analogue pipe temperature gauges for about £10 each and use these to check the flow and return temperatures.

Are you sure your immersion tank is only 50 litres? That sounds quite small.

On the oil price, I had hoped that prices would fall this summer on the back of some resolution to the terrible events in Ukraine. But unfortunately this seems increasingly unlikely and my own view now is that we are going to be stuck with high prices for quite some time. I bit the bullet a couple of months ago and filled our tank at £0.95 per litre including the 5% VAT. Best price in my area today is £1.03. 

Very useful info thanks. Should the flow and return temperatures from the boiler you mentioned for central heating be the same as the flow and return temperatures when using just the hot water? So if I put the boost on the hot water I want to be seeing 60 out and less than 54 back? Thanks 

Alfster

dunstonh said:

Heating a water cylinder doesn't take that long for a well lagged cylinder just needing bringing back up to temperature.  If your controller has separate timers for heating and water, then you probably only need 15-30 minutes for the water.

So, reduce the time the boiler is on for hot water.  Start at 30 minutes.   If you notice no reduction in temperature then reduce it to 25 minutes and repeat until you find the point where the water starts losing temp and go back to the point it doesn't.

Ours comes on for 20 minutes twice a day. And the oil use is tiny from May through to October.  it doesn't drop a bar on the Apollo meter.      Our immersion heater has no timer on it. So, it would need turning on/off manually and that risks being in longer than necessary wasting any tiny differences in price.

(We are heavy off-peak electricity users as we have an electric Aga which works like a big storage heater).

Same here. 30amp AGA.   Although we are lucky that our economy 7 timer is currently 8.56am to 3.56pm.  A few more powercuts and it will move to the evening and we will get cheap rate during peak hours.

Wait hang in, with the new price cap
increase you get a cheaper night economy 7 rate? We have an economy 7 meter but it’s still charged 30p rate for day or night so redundant now. 

lohr500

It is difficult to achieve the same flow and return temperatures when running the central heating vs just hot water.
When the central heating is running there is a lot more opportunity to dissipate heat through the radiators so the return water temperature will be lower.
But oil consumption is highest when running the central heating. So I set my system up to be optimised when the central heating is on.  If my flow temperature is 60 C, then even when heating the water only, there is a good chance the return will be below the magic 54 C, with a tank thermostat set to 55 C.
I believe modern gas boilers and controls can modulate the boiler output and even control the circulation pump speed to optimise the flow/return temperatures, but this isn't the case for most oil boiler installations.

dunstonh

Alfster said:

dunstonh said:

Heating a water cylinder doesn't take that long for a well lagged cylinder just needing bringing back up to temperature.  If your controller has separate timers for heating and water, then you probably only need 15-30 minutes for the water.

So, reduce the time the boiler is on for hot water.  Start at 30 minutes.   If you notice no reduction in temperature then reduce it to 25 minutes and repeat until you find the point where the water starts losing temp and go back to the point it doesn't.

Ours comes on for 20 minutes twice a day. And the oil use is tiny from May through to October.  it doesn't drop a bar on the Apollo meter.      Our immersion heater has no timer on it. So, it would need turning on/off manually and that risks being in longer than necessary wasting any tiny differences in price.

(We are heavy off-peak electricity users as we have an electric Aga which works like a big storage heater).

Same here. 30amp AGA.   Although we are lucky that our economy 7 timer is currently 8.56am to 3.56pm.  A few more powercuts and it will move to the evening and we will get cheap rate during peak hours.

Wait hang in, with the new price cap
increase you get a cheaper night economy 7 rate? We have an economy 7 meter but it’s still charged 30p rate for day or night so redundant now. 

Our billing shows 0.31414 for day and 0.18590 for night.   You haven't moved to a single rate tariff by any chance? (which would still use the day/night readings but charge them both at the same rate)

QrizB

Alfster said:

Wait hang in, with the new price cap
increase you get a cheaper night economy 7 rate? We have an economy 7 meter but it’s still charged 30p rate for day or night so redundant now. 

As dunstonh says, you'll only be charged the same for day and night if you've switched to a single-rate tariff rather than E7.

And 30p/kWh sounds like it's a legacy fixed rate; variable rates are currently around 28p/kWh for a single-rate tariff or 20-something night, 30-something day for E7, while new fixes are all 30-something night / 40-something day.

For example, EDF's standard variable rates are here and Octopus here; other suppliers are similar (as you'll see from those two examples, some suppliers have wider day/night spreads for E7, and some have narrower ones).

Alfster

dunstonh said:

Alfster said:

dunstonh said:

Heating a water cylinder doesn't take that long for a well lagged cylinder just needing bringing back up to temperature.  If your controller has separate timers for heating and water, then you probably only need 15-30 minutes for the water.

So, reduce the time the boiler is on for hot water.  Start at 30 minutes.   If you notice no reduction in temperature then reduce it to 25 minutes and repeat until you find the point where the water starts losing temp and go back to the point it doesn't.

Ours comes on for 20 minutes twice a day. And the oil use is tiny from May through to October.  it doesn't drop a bar on the Apollo meter.      Our immersion heater has no timer on it. So, it would need turning on/off manually and that risks being in longer than necessary wasting any tiny differences in price.

(We are heavy off-peak electricity users as we have an electric Aga which works like a big storage heater).

Same here. 30amp AGA.   Although we are lucky that our economy 7 timer is currently 8.56am to 3.56pm.  A few more powercuts and it will move to the evening and we will get cheap rate during peak hours.

Wait hang in, with the new price cap
increase you get a cheaper night economy 7 rate? We have an economy 7 meter but it’s still charged 30p rate for day or night so redundant now. 

Our billing shows 0.31414 for day and 0.18590 for night.   You haven't moved to a single rate tariff by any chance? (which would still use the day/night readings but charge them both at the same rate)

That’s a very good rate. When I plugged my details into uswitch which usually comes back with lots of different tariffs and companies it came back saying it could find nothing at all that would be better ☹️  

dunstonh

Alfster said:

dunstonh said:

Alfster said:

dunstonh said:

Heating a water cylinder doesn't take that long for a well lagged cylinder just needing bringing back up to temperature.  If your controller has separate timers for heating and water, then you probably only need 15-30 minutes for the water.

So, reduce the time the boiler is on for hot water.  Start at 30 minutes.   If you notice no reduction in temperature then reduce it to 25 minutes and repeat until you find the point where the water starts losing temp and go back to the point it doesn't.

Ours comes on for 20 minutes twice a day. And the oil use is tiny from May through to October.  it doesn't drop a bar on the Apollo meter.      Our immersion heater has no timer on it. So, it would need turning on/off manually and that risks being in longer than necessary wasting any tiny differences in price.

(We are heavy off-peak electricity users as we have an electric Aga which works like a big storage heater).

Same here. 30amp AGA.   Although we are lucky that our economy 7 timer is currently 8.56am to 3.56pm.  A few more powercuts and it will move to the evening and we will get cheap rate during peak hours.

Wait hang in, with the new price cap
increase you get a cheaper night economy 7 rate? We have an economy 7 meter but it’s still charged 30p rate for day or night so redundant now. 

Our billing shows 0.31414 for day and 0.18590 for night.   You haven't moved to a single rate tariff by any chance? (which would still use the day/night readings but charge them both at the same rate)

That’s a very good rate. When I plugged my details into uswitch which usually comes back with lots of different tariffs and companies it came back saying it could find nothing at all that would be better ☹️  

That is the exc-VAT rate.  Inclusive of VAT is 0.195195 and 0.329847 respectively.  It is the Bulb variable rate which is at the current cap level.

EcoScruples

I've been taking readings over the last few months and i use 1.2 litres of oil on average a day to heat my water cylinder using 2 x 30 min periods running my Oil boiler once in the morning, once in the evening. This gives me enough hot water to do the average stuff needed.
I normally do this for 6 months of the year when i dont run the heating.
Using my Immersion heater I need to run it around 50 mins a day to heat the cylinder. This again gives me all the hot water I need for general usage.

With solar it makes more sense to use electric to heat water in spring, summer and the boiler in autumn, winter (As I run the heating anyway so no extra cost).

Reed_Richards

EcoScruples said:

With solar it makes more sense to use electric to heat water in spring, summer and the boiler in autumn, winter (As I run the heating anyway so no extra cost).

That doesn't seem right.  There will always be an extra cost to heat your hot water with your oil boiler, but when you run your heating as well you won't be able to tell what it is.