Back Boilers - heating water and CH at same time cheaper?

ReflexReaction

Just a thought, but should I be running my hot water and my central heating at the same time? I have a Baxi back boiler, and I just wondered if having them both heating up at the same time actually saves money?

I would imagine as the heating element is hot anyway, then there would be good savings in doing this? Or have I missed the point?

I used to have a combi boiler in my old house, so I am trying to understand the best ways to run a back boiler. The back boiler we have heats up both our CH system and a HW tank in the loft. We are often running out of hot water, so I've set the HW to come on for a few hours a day now - 1.5 in morning and 1.5 in evening - does this sound like too much?

Thanks for any help as always,

RR :beer:

macman

No, it doesn't save money, because heating up the DHW as well means using more gas to do so. Any residual heat used to heat the water is not used to heat the house.
The only 'saving' is that the heat lost from the hot tank is not actually wasted, but serves to heat the house a little.
A combi is entirely different, as it heats the DHW only on demand, and while doing so does not provide any CH at all.

ReflexReaction

Cool, thanks for the reply. So there is no benefit, nor negative impact of heating the HW at the same times as the CH with a back boiler.

HappyMJ

ReflexReaction wrote: »

Cool, thanks for the reply. So there is no benefit, nor negative impact of heating the HW at the same times as the CH with a back boiler.

The savings would only be pennies anyway due to the boiler already being hot and not having to heat up a few litres of water in the pipes before heating the water in the cylinder. So set the hot water however you want. I'd personally set the hot water to 24/7 operation so that you never run out of hot water and when a bath is taken the water is immediately reheated.

ReflexReaction

Surely that would be expensive?

HappyMJ

ReflexReaction wrote: »

Surely that would be expensive?

Well yes and no depending on your definition of expensive and convenience..I've tried it. The cylinder loses about 2kWh of heat per 24 hour period when set to a constant temperature. If no water is drawn off the boiler automatically comes on about twice a day and increases the temperature of the water about 5 degrees it then takes another 12 hours for the water temperature to drop and the thermostat to request the boiler for more heat. If hot water is drawn off the thermostat detects the drop in temperature and immediately reheats the water but the standing losses are 2kWh per day. I'd rather have hot water available at all times for hand washing etc and as gas only costs 3.5p/kWh the increased energy usage is only about 1kWh per day as opposed to the heat loss compared to a warm rather than hot cylinder. Yes it costs more but it isn't much at about £1 per month. Is it expensive? Maybe...but I don't think it's much.

ReflexReaction

I see! I guess my next question is how to ensure that the boiler waits until the temp has dropped 5c before attempting to re-heat the water? My back boiler is either on or off - if I turn hot water on, it seems to do things

southcoastrgi

it depends if your back boiler & system is fully pumped ? because alot of back boilers work on a gravity system so whenever your heating is on so is the hotwater (a pump kicks in for your heating the h/w just works by gravity circulation)

ReflexReaction

Well, the system has seperate controls - it allows me to have the hot water on without the central heating - suggesting both are seperate and pumped?

I would be keen to leave the hot water on all day if it was really only going to cost me £1 a month!

Cardew

At this time of the year the 2kWh heat loss from the tank every 24 hours isn't 'lost' as such because it warms the fabric of the house.

ReflexReaction

My tank is in the loft so yep it's deffo lost