What is best way to run high efficiency boiler?

bwanger2012

Hiya everyone, long time lurker and wondered if anyone can offer any advice. I have read all sorts of posts on here and other internet forums, but cannot seem to get an answer to my specific question. If you turn the flow temperature up on a high efficiency boiler, to say, 70 -75 degrees, the return temperature exceeds 55, so the boiler is no longer fully condensing, so my question would be, not in terms of % efficiency, but in terms of ££ for an average cost of gas, how much more would this cost? I know its kind of a "how long is a piece of string" question, but in other people's experience, does it make a huge difference? I normlly run the boiler on a 60 degree flow, but now the weather is colder it takes ages for the house to warm up, so I turned it up to 70 (80 is max) and its much warmer now, return hovers around 57-60 degrees, flue gases exit flue at approx 49 degrees (measured with laser thermometer). We are on a tight budget, so i cant afford to be hit with a huge catchup bill come the new year, but we don't want to be cold either, so it's striking that balance! Thanks again in advance.

daveyjp

To see what the difference may be take gas meter readings. You just need to ensure the internal starting air temp and external air temp are similar two days running.

rogerblack

The difference will be small.
Perhaps 10% at the absolute outside.
The most economic way of maintaining the house at a constant temperature is to keep the boiler on 24h, and adjust the output to maintain as low a loop temperature as possible.

If you want to turn the heating up/down automatically, it gets way more complex to work out.
Speaking in general, it's 'always' going to be cheaper to heat a property rapidly from a colder temperature, than to start heating it earlier than you need slowly so it reaches temperature at the same time.
Even taking into account the lower efficiency.

Cardew

daveyjp wrote: »

To see what the difference may be take gas meter readings. You just need to ensure the internal starting air temp and external air temp are similar two days running.

The problem with that comparison is that the heat absorbed by the fabric of the house on the first day distorts the figures for the second day.

The OP 's question has been raised before on MSE without a satisfactory answer.

Indeed what is the effect of varying the heating load e.g. heating reception rooms only during the day and in the evening turning on bedroom radiators; or with a system boiler(i.e. not a combi) heating hot water.

I suspect there is no 'one size fits all answer' to the dilemma; but my gut feeling is the differential between 60C and 70-75C will be quite small and hopefully well below the 10% mentioned above.

gas4you

By setting the boiler to 70c, the rads heat up more, the rooms heat up quicker so will turn the room thermostat/trv's off quicker, thereby saving you some money.

If the boiler temp is too low, then it will chugging away all day and the rooms will never get warm enough to shut the stats off.

With a flow of 70c, the return should be around 50c with proper balancing.

Cardew

gas4you wrote: »

With a flow of 70c, the return should be around 50c with proper balancing.

Surely the problem is you can balance the system with all radiators in use; but what happens to the return temperature if most of the radiators are switched off? - the latter situation would be normal most of the day.

bwanger2012

thanks guys, well I'm leaving it set to 70. We've also noticed the house is warm yet the boiler isn't firing as much so all good

gas4you

Cardew wrote: »

Surely the problem is you can balance the system with all radiators in use; but what happens to the return temperature if most of the radiators are switched off? - the latter situation would be normal most of the day.

In theory each radiator should be set for a 20c drop, therefore the system itself should achieve this drop whatever radiators are in use.

Whether this works in practice is another thing, as we all know about theory!!

Personally I just get as close as I can in the time available.