is it cheaper to reduce rads or boiler temp

joesoap1 · 6 Dec 2010

Hi, Been monitoring my gas consumption

and as I have 11 rads running at lowest setting on boiler, 50 degrees, I was wondering if I turned half rads off and upped boiler to 70 degrees, which would be most economical? All rads are trv except small bathroom 1, and at this weather, rads always on, rooms never come up to temp to shut trv.s down. big rooms;Any advice appreciated, on how boiler copes?

ianniann · 6 Dec 2010

A condensing boiler will run more efficiently pushing low temperature water into a lot of radiators (or a few oversized radiators), but this won't save you more than about 5%. With a non-condensing boiler it won't make much difference. Turning off radiators (or turning down the TRV) in rooms you don't need warm will save more, but if you need to heat up the room again later each day (eg. a bedroom) then it isn't really worth the effort. If you do plan to leave some rooms colder then make sure you shut the doors.

D_Hailsham · 6 Dec 2010

joesoap1 said:
Hi, Been monitoring my gas consumption and as I have 11 rads running at lowest setting on boiler, 50 degrees, I was wondering if I turned half rads off and upped boiler to 70 degrees, which would be most economical? All rads are trv except small bathroom 1, and at this weather, rads always on, rooms never come up to temp to shut trv.s down. big rooms;Any advice appreciated, on how boiler copes?

Systems are traditionally designed for a lowest outside temperature of -1°C and a room temperature of 21°C.

With temperatures dropping to -8°C or lower, the highest you will get your room up to is about 15°C - unless the system is considerably oversized.

If you are running the boiler at 50°C the rad output will only be 35% of the manufacturer's stated output and at 70°C it will be 82%.

TRV's will only work if the radiators are giving off enough heat to bring the room up to temperature. If you are running at 50°C, this will never happen.

Turning rads off is not effective as the room will still get heated by transmission through the internal walls.

What controls do you have apart from the boiler thermostat and TRVs on the radiators?

ianniann · 6 Dec 2010

Turning rads off is not effective as the room will still get heated by transmission through the internal walls.

You keep saying that but I have to wonder if you've ever tried it? Turn off all the radiators upstairs and see if it warms up nicely just by heat coming from downstairs. It doesn't. I used to live in a house without central heating.

Of course the unheated parts of the house won't be as cold as outside, but it will be a whole lot colder than if you had the heating on. That's the whole point of TRVs, after all! If every room in the house warmed up to the same temperature just because the walls weren't insulated then TRVs would be pointless. My point: if you don't need a room to be heated then don't heat it.

The rest of the reply is correct. If the rooms don't stay warm with the radiators at 50C then make them warmer (and insulate too if you can). When the weather warms up you should turn the boiler temperature back down to the lowest level that works well for you.

joesoap1 · 6 Dec 2010

D_Hailsham said:
joesoap1 said:

Hi, Been monitoring my gas consumption and as I have 11 rads running at lowest setting on boiler, 50 degrees, I was wondering if I turned half rads off and upped boiler to 70 degrees, which would be most economical? All rads are trv except small bathroom 1, and at this weather, rads always on, rooms never come up to temp to shut trv.s down. big rooms;Any advice appreciated, on how boiler copes?

Click to expand...

Systems are traditionally designed for a lowest outside temperature of -1°C and a room temperature of 21°C.

With temperatures dropping to -8°C or lower, the highest you will get your room up to is about 15°C - unless the system is considerably oversized.

If you are running the boiler at 50°C the rad output will only be 35% of the manufacturer's stated output and at 70°C it will be 82%.

TRV's will only work if the radiators are giving off enough heat to bring the room up to temperature. If you are running at 50°C, this will never happen.

Turning rads off is not effective as the room will still get heated by transmission through the internal walls.

What controls do you have apart from the boiler thermostat and TRVs on the radiators?

Hi, Thanks for reply.No Hoeywell, been in house 15 years, boiler was not long in before, so I didn,t bother.The shape and size of the house,to me, doesn,t merit one.Dormer bungalow, z shaped, conservatory,which in summer is where we are,. Now in lounge, conservatory frozen inside a couple of times in last 2 weeks, never before,double glazed throughout. Loft just done again last year.12" now.No cavity insulation, random stone, also,suffer with condensation.badly.Had a large Dehumidifier running 24/7 for last 3 months, hardly any water now in it, cuts out ,signifying air dry, but windows still wet, God knows why?It,s a cold house, plenty air bricks, .trying to reduce it with both heating and dehumid, exceptionally cold,-17 here last night.To run all rads at 50c, 24/7 is working out at approx £7+ per day.Electric £1.50 per day.mostly for dehumidifier.I do go round tuning some off, when sun shines in room.It,s like chasing your tail.Contemplating boiler chane next year.Got Vokera rs80 flowmatic, good boiler.Iffy??about changing.serviced every year.Think that,s about all.cheers.Open to suggestions.PS Need to keep all doors open for dehumidifier to operate effectively.Catch 22.& it,s 13 rads, not 11.Seneility creeping in;;

tryitandsee · 6 Dec 2010

Try and get rid of the source of water vapour in the bungalow. Perhaps a mechanical vent in bathroom, kitchen and any other room for drying clothes etc. Try and take out moist air but not let cold air in!

gas112 · 7 Dec 2010

Dhailsham is getting mixed up if it is minus 8 outside it does not mean it will only get to 15 . The -1 to 21 degrees is within an hour so with a lower outside temp it just takes longer.

CH is designed that each room next to each other will be heated to a certain temp and heat loss through what walls floors and glass areas taken into account. So there is a heat transferance through walls ceilings etc.

Running at 50 will never get the house hot better to turn boiler up and have the roomstat lower that is where you will save money as the house will get warm/hot and the roomstat will turn the boiler off

joesoap1 · 7 Dec 2010

tryitandsee said:
Try and get rid of the source of water vapour in the bungalow. Perhaps a mechanical vent in bathroom, kitchen and any other room for drying clothes etc. Try and take out moist air but not let cold air in!

Got Cooker fan, bathroom extractor fan,& dehumidifier, and still condenstion.Dry clothes in tumbler/ in shed.Lots of windows in the house.Every winter is the same, that,s why I invested in the dehumidifier last year.It,s set to auto, so cuts out when humidity is low, yet wndows stream with water, and dehumidifier swithed itself off.It's aconundrum.Only two in the house.cheers

joesoap1 · 7 Dec 2010

gas112 said:
Dhailsham is getting mixed up if it is minus 8 outside it does not mean it will only get to 15 . The -1 to 21 degrees is within an hour so with a lower outside temp it just takes longer.

CH is designed that each room next to each other will be heated to a certain temp and heat loss through what walls floors and glass areas taken into account. So there is a heat transferance through walls ceilings etc.

Running at 50 will never get the house hot better to turn boiler up and have the roomstat lower that is where you will save money as the house will get warm/hot and the roomstat will turn the boiler off

Hi, never had a room stat, as described, house such a strange shape, + condensation means I need all doors open for dehumidifier to operate efficiently.CANNOT get rid of condensation, just that type of house, lots of glass.Baffles me where it all comes from.If I change boiler to condenser, in spring, will have roomstat fitted then.House is more, Open Plan, so roomstat not effective???? or am I wrong???cheers

D_Hailsham · 7 Dec 2010

gas112 said:
Dhailsham is getting mixed up if it is minus 8 outside it does not mean it will only get to 15 . The -1 to 21 degrees is within an hour so with a lower outside temp it just takes longer.

That will only be true if the system is considerably oversized. Most systems are oversized by 10-15% to provide faster warming up times, but if the outside temperature drops too much all the spare heat is used up and the heating up time gets longer.

An example:

House needs 22kW (no oversizing) to maintain a temperature of 21°C when it is -1°C outside. If the boiler is system is oversized by 15%, i.e 25.3kW, it will be able to maintain 21°C when the outside is -4.3°C, but the heating up time will be longer. If it is -8°C outside the 22kW boiler will still only be able to raise the temperature by 22°C, i.e to 14°C and the 25.3kW will get it up to 17.3°C. It doesn't matter who long you wait, the house will never reach 21°C.

joesoap1 · 7 Dec 2010

D_Hailsham said:
gas112 said:

Dhailsham is getting mixed up if it is minus 8 outside it does not mean it will only get to 15 . The -1 to 21 degrees is within an hour so with a lower outside temp it just takes longer.

Click to expand...

That will only be true if the system is considerably oversized. Most systems are oversized by 10-15% to provide faster warming up times, but if the outside temperature drops too much all the spare heat is used up and the heating up time gets longer.

An example:

House needs 22kW (no oversizing) to maintain a temperature of 21°C when it is -1°C outside. If the boiler is system is oversized by 15%, i.e 25.3kW, it will be able to maintain 21°C when the outside is -4.3°C, but the heating up time will be longer. If it is -8°C outside the 22kW boiler will still only be able to raise the temperature by 22°C, i.e to 14°C and the 25.3kW will get it up to 17.3°C. It doesn't matter who long you wait, the house will never reach 21°C.

Hi, by system I presume you mean boiler output? If I change, 30kw is what I deem to require for 13 rads.Do you think so?

D_Hailsham · 7 Dec 2010

joesoap1 said:
D_Hailsham said:

gas112 said:

Dhailsham is getting mixed up if it is minus 8 outside it does not mean it will only get to 15 . The -1 to 21 degrees is within an hour so with a lower outside temp it just takes longer.

Click to expand...

That will only be true if the system is considerably oversized. Most systems are oversized by 10-15% to provide faster warming up times, but if the outside temperature drops too much all the spare heat is used up and the heating up time gets longer.

Click to expand...

Hi, by system I presume you mean boiler output? If I change, 30kw is what I deem to require for 13 rads.Do you think so?

No; the system is the boiler and radiators. If you have 13 rads you will only have about 20kW at the most. There is no point putting a 30kW boiler onto 20kW of rads as you will still only get 20kW of heat. You have to match the boiler to the rads; though not for combi boilers as they are sized for hot water requirement.

You should do a boiler sizing calculation using Boiler Size Calculator and check the output of your rads using Stelrad Elite Catalogue. Then Post the results.

joesoap1 · 7 Dec 2010

D_Hailsham said:
joesoap1 said:

D_Hailsham said:

gas112 said:

Dhailsham is getting mixed up if it is minus 8 outside it does not mean it will only get to 15 . The -1 to 21 degrees is within an hour so with a lower outside temp it just takes longer.

Click to expand...

That will only be true if the system is considerably oversized. Most systems are oversized by 10-15% to provide faster warming up times, but if the outside temperature drops too much all the spare heat is used up and the heating up time gets longer.

Click to expand...

Hi, by system I presume you mean boiler output? If I change, 30kw is what I deem to require for 13 rads.Do you think so?

Click to expand...

No; the system is the boiler and radiators. If you have 13 rads you will only have about 20kW at the most. There is no point putting a 30kW boiler onto 20kW of rads as you will still only get 20kW of heat. You have to match the boiler to the rads; though not for combi boilers as they are sized for hot water requirement.

You should do a boiler sizing calculation using Boiler Size Calculator and check the output of your rads using Stelrad Elite Catalogue. Then Post the results.

Hi, Thanks for reply.My boiler is 28kw heating input,24kw output.vokera rs80 combi.1bathroom/1 shower-room.never used together;What Valiant-eco is comparative?cheers

gas112 · 7 Dec 2010

DHailsham i guess every house i work in must be oversized then because no one has had trouble getting there house hot even in this weather.
I suggest you do a little more reading on heating design the 21 figure is within the hour not a max temp with minus 1 outside , it was minus 12 last night and my heating had no trouble achieving mid 20`s and its not over sized

joesoap1 · 8 Dec 2010

gas112 said:
DHailsham i guess every house i work in must be oversized then because no one has had trouble getting there house hot even in this weather.
I suggest you do a little more reading on heating design the 21 figure is within the hour not a max temp with minus 1 outside , it was minus 12 last night and my heating had no trouble achieving mid 20`s and its not over sized

Hi Gas112, As an experiment yesterday I monitored my CH.All 13 rads on, @, 50 degrees, lowest boiler setting was £10 for 24 hours, gas used.turned boiler up to half, 75 degrees, plenty hot enough, and spare capacity, £15 per day.That's not cheap, £100 pw, and it was -10c here.When I bought this house, there was 6, rads. I added another 7, so boiler was way too big at first, but plenty big enough now, with spare.Temps won,t dip much lower than last two weeks in thiscountry???Does that seem excessive consumption, and do you think I would benefit greatly from a change to a condenser?

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is it cheaper to reduce rads or boiler temp

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