CH and DHW at same time - more efficient?

liviboy

Hi there,


Bit of a daft question but will help to solve a 'pub argument'.


Is it more efficient to have the CH and DHW both on at the same time. Its a hot water cylinder tank - no combi boiler obviously.


Both the tank and CH have thermostats so when either gets to temp the heating will adjust accordingly.


I don't think it makes any difference as the energy needed is the same but my "bar" friend insists otherwise...


Cheers all :-)

Andy_WSM

I'd have said marginally more efficient to have them both on at the same time as the water in the heating circuit is being heated anyway and if it's a condensing boiler the cooler return temperature caused by heating the tank and the radiators at the same time will make the boiler condense (more efficient) for longer.

Realistically though - the savings in a month probably won't buy the pint you discussed this over!

liviboy

Andy_WSM wrote: »

I'd have said marginally more efficient to have them both on at the same time as the water in the heating circuit is being heated anyway and if it's a condensing boiler the cooler return temperature caused by heating the tank and the radiators at the same time will make the boiler condense (more efficient) for longer.

Realistically though - the savings in a month probably won't buy the pint you discussed this over!

Perhaps not - but your post is worth a pint for me haha! :beer:
Cheers for the quick reply:j

AndyPK

Certainly will small boilers its best to have the hot water on at least 10 mins before the heating, so get the water hot quickly.

Small boilers struggle to heat both up from a cold morning start.

If your talking about the evening with both pinging off the thermostats then its not much different

Cardew

That is a variation on the normal question posed. Some people think that if the CH is on to heat one radiator, it is as cheap to heat all 20 radiators!


As indicated above, you don't 'get owt for nowt'. It still takes the same amount of energy for the CH and the hot water, regardless of them being on together or separately. There might be marginal increases in efficiency.

dogshome

Have oil fired Heat & Hot water so whilst not the same fuel, I had the same problem of high fuel cost with the Hot Water cylinder needing to be full of hot water first thing in the morning, with the boiler also heating the rads at the same time in winter.

I reasoned that the boiler had only so much output, and doing 2 things at once meant that it wasn't at peak efficiency for either of them. My solution was to set the timer for hot water only for 90 mins in the early hours of the morning, with heating thermostat set to zero last thing at night

This cut my oil consumption by 20% - Of course it's a bit chilly for the first one up in the morning who has to turn the heating on, but as that is usually me and I pay the bills, I'm happy to accept that.

AndyPK

I would have thought you would only need between 30-60mins.

You probably want to get yourself a programmable room stat. This is a timer and thermostat in one. It will then turn your heating on for you in the morning after your ~90mins.
It will also allow you to set lower temperatures during the day, so very worth while if your home during the day.

Something like this: (but these can be painful to programme)

http://www.ebay.co.uk/itm/DRAYTON-DIGISTAT-3-22083-7-DAY-PROGRAMMABLE-ROOM-THERMOSTAT-/321575416362?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item4adf63722a

http://www.ebay.co.uk/itm/DRAYTON-DIGISTAT-3-22087-MAINS-POWERED-/301367892801?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item462aed1b41

http://www.ebay.co.uk/itm/DRAYTON-DIGISTAT-2-24-HOUR-PROGRAMMABLE-THERMOSTAT-MAIN-/311163466339?pt=UK_DIY_Materials_Plumbing_MJ&hash=item4872c9b263