Does 'water and heat' setting burn more oil?

kathykate_2

At the moment we have our oil boiler on for one hour morning and night to heat water only. This may sound like a daft question but If I switch it to 'water and heating', will it burn more oil? Only reason I ask is that in the winter when it is set to to this, it doesn't seem to be burning more than if it was just doing the hot water. Was wondering if I can squeeze a little heat out of it on these chilly days! Cheers!

malc_b

It the energy is going into the hot water then it isn't heating the house so yes it does use more oil. The owt for nowt principle.

However, if it is being woefully inefficient heating the hot water then adding the house load may help that and therefore you'll heat the house with what goes to waste. Oil boilers have a constant power output, unlike some gas ones which can vary. And the best way to run them is one for as long as possible. Starting wastes oil. So if heating the water is a load of on/off/on/off etc. you could be wasting a load of oil. Adding the house load will give on..............off which is better.

FYI my timer is set to heat my water on 10min, off 10min, repeat 4 times at 5am, 2 times at 2:30pm. With only the hot water as load. I found (trial and error) that with this the boiler runs solid for the 10mins. Any longer or shorter wait and it cycles every 2 mins. The heating bursts are just enough to ensure the tank is full of hot water for when it is needed.

kathykate_2

Cheers again for info.

From what you're saying I'm gathering this... if the boiler is switching on/off/on/off whilst heating the water, it would be best to add the heating to it so it just goes on....... keeps on.... then finally off.

Thing is, even with our heating added, our boiler always does the on/off thing, it never stays on burning constantly, even when the inside temperature is less that what the thermostat say we want it to be.

Also am not clear about the times you've worked out is best for just water is it like this? On (for just water) at 5am, off at 5.10, on at 5.20, off at 5.30, on at 5.40, off at 5.50, on at 6pm, off at 6.10, on at 6.20 and off at 6.30.

Then again on at 2.30pm, off 2.40, on 2.50, off 3pm, on 3.10, off 3.20?

Just want to be clear as maybe these settings will be good for us too! Coz that means a total 'on' time of 80 mins whereas we are doing 120 mins at the moment.
Double cheers!

malc_b

The boiler will never run constantly unless the weather is really cold. Look at this way. Say firing the boiler wastes 10p of oil. If the total burn is 30p of oil then that's 66% efficiency to start with, let alone other boiler losses. But if the total burn is 100p of oil then that is 90% efficiency, 26% decrease in oil usage.

Yep your times are right. A right pain to put in on the timer. On my system the boiler runs continuously for those 10mins. The water heats up and at some point the tank thermostat tells the system job done so the last burn will to be shorter than 10min. The only way you can tell if it works on your system is to try it.

I should mention controls as you may not have some of these. All boilers will have a water temperature cut-out. When water flowing through the boiler reaches 80-90C (AFAIR) the burner turns off. When it cools down the burner fires up again. Very old systems just have that and the boiler sits there going on/off/on etc. with hot water tank being gravity fed (not pumped) so takes ages to warm.

Modern systems are fully pumped, even the hot water tank. And when the pump is off the boiler is switched off too so it doesn't sit there heating itself. There should also be a thermostat on the hot water tank to tell the system when the hot water tank has reached temperature. This should have a wide on/off difference so once the tank is hot it doesn't turn on again for quite a time.

On mine if I run the hot watee continuously the boiler water temperature stat cycles the boiler every 2 minutes. With my 10/10 I run for 10minutes continuously.

The final control is the hall/lounge thermostat. This turns on the heating when it is cold and off when it reaches temperature. You can get more intelligent versions of these that work out the boiler needs to run for say 50% of the time to keep the house at the set temperature, then they give 7.5min of burn every 15min. That's more efficent than quick on/off/on.