Heat one room only, using gas combi boiler. Wasteful?

macman

It's the dew point that determines the return temp at which the boiler will run in condensing mode.
Typically this is at around 55C in the UK.

Yorkshire_Pud

chris_n said:

Just be careful running a 2kW load for an extended period of time through a plug, especially so with an extension. Plugs can start to warm up especially if anything is at all loose, especially fuse holders. Usually heating appliance manufacturers say not to use an extension.
I'm sure it's not a problem if you use good equipment and check regularly for signs of anything getting hot. Just something to bear in mind.

Thanks extension would only be so I can use my plug in big sized electricity use measurer as socket in an awkward place, I can plug the radiator in to a, glug, adaptor or take the adaptor out (good idea I think), only has a little radio sharing. I tend to keep the kw down below 2 and rad has a thermostat on it too but good advice anyway as I never take it for granted if it plugs in it’s safe!

Yorkshire_Pud

QrizB said:

ariarnia said:

i remember reading somewhere there had to be at least 10 degrees of difference between the in and out flow for the 90 plus % efficiency to happen. 

That's folklore, not fact. Whether the boiler condenses properly or not is really down to the return temperature being cold enough. It doesn't matter whether it's going out at 70C and coming back at 50C, or going out at 52C and coming back at 50C.

i was actually wondering about efficiency with condensing boilers if only one rad is on.

The issue is that one radiator might only be able to dissipate (say) 1Kw, while your boiler might only be able to modulate down to (say) 5kW. This means that the boiler will cycle on and off, being on only 20% of the time. Cycling reduces efficiency for various reasons (including the purge air that is blown through your combustion chamber with each cycle).

So if only one radiator in use better to set the flow down towards the 45C optimum and open the radiator thermostat up higher rather than higher flow temp and restricted thermostat on the rad?

chris_n

Yorkshire_Pud said:

QrizB said:

ariarnia said:

i remember reading somewhere there had to be at least 10 degrees of difference between the in and out flow for the 90 plus % efficiency to happen. 

That's folklore, not fact. Whether the boiler condenses properly or not is really down to the return temperature being cold enough. It doesn't matter whether it's going out at 70C and coming back at 50C, or going out at 52C and coming back at 50C.

i was actually wondering about efficiency with condensing boilers if only one rad is on.

The issue is that one radiator might only be able to dissipate (say) 1Kw, while your boiler might only be able to modulate down to (say) 5kW. This means that the boiler will cycle on and off, being on only 20% of the time. Cycling reduces efficiency for various reasons (including the purge air that is blown through your combustion chamber with each cycle).

So if only one radiator in use better to set the flow down towards the 45C optimum and open the radiator thermostat up higher rather than higher flow temp and restricted thermostat on the rad?

You would still get the boiler cycling problem though. I have never believed in this heat one room only thing. If you only heat one room you get the boiler cycling problem and efficiency the rest of your house becomes the outdoors (maybe not quite but significantly lower temperatures) with only internal walls and doors with no seals between you and the cold. As soon as you open the door the temperature tries to equalise so half of your heat is lost. If you allow radiators in the surrounding spaces to become warm you can keep the boiler running efficiently and benefit from 2.5 to 3 times (allowing for cost difference and efficiency) the heat that your electric radiator can produce for the same cost. This will help keep internal walls etc warmer so your heat won't dissipate as quickly.

ariarnia

we find having the hole house heated to a lowish temp (16 in our case) works well for us and doesn't cost much. we then have a wood stove in the lounge but you could just have the rad in the one room higher. 

we found when we tried heating the hole house to 10 (the lowest we've tried) then the heat loss from the lounge was a lot faster than at 16. and we find 16 a comfortable temp for getting ready for bed. to much lower and no one wants to get up in the morning

Yorkshire_Pud

chris_n said:

Yorkshire_Pud said:

QrizB said:

ariarnia said:

i remember reading somewhere there had to be at least 10 degrees of difference between the in and out flow for the 90 plus % efficiency to happen. 

That's folklore, not fact. Whether the boiler condenses properly or not is really down to the return temperature being cold enough. It doesn't matter whether it's going out at 70C and coming back at 50C, or going out at 52C and coming back at 50C.

i was actually wondering about efficiency with condensing boilers if only one rad is on.

The issue is that one radiator might only be able to dissipate (say) 1Kw, while your boiler might only be able to modulate down to (say) 5kW. This means that the boiler will cycle on and off, being on only 20% of the time. Cycling reduces efficiency for various reasons (including the purge air that is blown through your combustion chamber with each cycle).

So if only one radiator in use better to set the flow down towards the 45C optimum and open the radiator thermostat up higher rather than higher flow temp and restricted thermostat on the rad?

You would still get the boiler cycling problem though. I have never believed in this heat one room only thing. If you only heat one room you get the boiler cycling problem and efficiency the rest of your house becomes the outdoors (maybe not quite but significantly lower temperatures) with only internal walls and doors with no seals between you and the cold. As soon as you open the door the temperature tries to equalise so half of your heat is lost. If you allow radiators in the surrounding spaces to become warm you can keep the boiler running efficiently and benefit from 2.5 to 3 times (allowing for cost difference and efficiency) the heat that your electric radiator can produce for the same cost. This will help keep internal walls etc warmer so your heat won't dissipate as quickly.

So effectively the increased efficiency of my boiler gives me more heat to more areas of the house via more radiators for the same spend on gas as just heating one room. If not exactly then as a general principal. A cycling boiler burns more fuel for less heat output?

Im going to draught strip the door from the hall (freezing) to the sitting room (warm with the radiator on) I could feel the very cold air being pulled in to the sitting room last night whenI had the open fire going and heating off to see how warm I could get it. I know an open fire pulls more cold air in because it needs air to burn but it was good to accentuate the problem for research. It has a baffle so I can close the chimney when not in use but when in use it takes about 12 hours to stop smoking so the chimney stays open and any gas heating goes up the chimney. I’m very quick going from room to room but ultimately I would rather go from one room to another without feeling I’m in the ice age from a warm place. I did always have low heat on in rooms but this year became scared of the insane cost of energy.

This is a work in progress for me I’m trying to learn what works and what doesn’t. The energy saving trust says it can be economical to heat one room if that room is less then a quarter of the house floor area.

Im going to put a few rads on tonight and see if my useage goes up. No smart meter so not an exact science!

QrizB

Yorkshire_Pud said:

chris_n said:

You would still get the boiler cycling problem though. I have never believed in this heat one room only thing. If you only heat one room you get the boiler cycling problem and efficiency the rest of your house becomes the outdoors (maybe not quite but significantly lower temperatures) with only internal walls and doors with no seals between you and the cold. As soon as you open the door the temperature tries to equalise so half of your heat is lost. If you allow radiators in the surrounding spaces to become warm you can keep the boiler running efficiently and benefit from 2.5 to 3 times (allowing for cost difference and efficiency) the heat that your electric radiator can produce for the same cost. This will help keep internal walls etc warmer so your heat won't dissipate as quickly.

So effectively the increased efficiency of my boiler gives me more heat to more areas of the house via more radiators for the same spend on gas as just heating one room. If not exactly then as a general principal.

In my opinion it will still cost more to heat extra rooms than to only heat one, just not as much more as you would think.

Yorkshire_Pud said:

A cycling boiler burns more fuel for less heat output?

I wouldn't go that far. A cycling boiler burns more fuel for a given heat output than a different non-cycling boiler would, but it still burns less fuel than that particular boiler would if it ran continuously at its lowest output.

chris_n

Not the increase efficiency but the fact that electricity is 3 times the price of gas. If you run your oil filled radiator at 2kW for one hour you will have 2kWh of heat added to your room for the cost of 2 units (kWh) of electricity so 70p.
If you run your boiler and it modulates to 6kw and run that for 1 hour it will add 5kWh ish (allowing for efficiency reduction)  for a cost of about 65p. Note that when you first turn the boiler on it will not modulate until the system is up to temp but you will still get more heat into the house for the same money.
 Many people panic when they see what the first half hour has cost, totally missing that subsequent half hours will be maybe a third of the cost. If you only have one radiator turned on and can't dissipate the 6kW of heat then your efficiency will be less so you maybe only get 4kWh for the same cost as your 2kWh radiator. 

Astria

Another thing you need to remember is that rooms are typically very poorly insulated, but your property is typically very well insulated, so having one warm room and all the other rooms unheated, that room will lose heat very quickly. The higher the temperature of the other rooms, the less heat you'll lose in your heated room.

If your room is small and you radiators are old, they might only be outputting 500W.

Remember to think about condensation - the lower the temperature of a room, the less amount of water can be contained in that air, so you need to manage the humidity in that room to ensure condensation doesn't cocur.

Yorkshire_Pud

Astria said:

Another thing you need to remember is that rooms are typically very poorly insulated, but your property is typically very well insulated, so having one warm room and all the other rooms unheated, that room will lose heat very quickly. The higher the temperature of the other rooms, the less heat you'll lose in your heated room.

If your room is small and you radiators are old, they might only be outputting 500W.

Remember to think about condensation - the lower the temperature of a room, the less amount of water can be contained in that air, so you need to manage the humidity in that room to ensure condensation doesn't cocur.

My property is not well insulated being old with solid walls. I don’t mind slightly draughty bedroom as warm in bed and some fresh air. Sitting room is single story with suspended floor and two external walls. Radiator is quite new, double and 1.6 metres long and heats the room up really well but I think Inpay for the privilege in gas used. I’m going to draught strip the internal door to sitting room. I may well move to the kitchen for daytime life  from December as it has a solid floor and in the summer is the coolest room in the house therefore the best insulated and should use less gas, decent old rad on an internal wall and some low level skirting heating. Door to outside weather stripped andI think  I will get a thermal curtain behind it to trap air and decrease conductivity of cold air, probably a pelmet over so the top isn’t an escape route.

Today I’m trying the low level heat in each room and will look after 24 hours, suspect it will increase my gas use a lot even if the place is more pleasant to be in the lack of insulation to external walls means it will always leach heat out unless I refit the whole house, not something I can contemplate right now hence my one cosy room idea!