I have two questions that I am sure you can help me with.
I have been told that it is a requirement to have a room thermostat on the heating system even if every radiator has a thermostatic valve. Is this the case? It would seem to be a nonsense.
Because of the proposed ground floor location of our new hot water cylinder our Aga will not be able to heat it on a gravity thermosiphon. One installer said a simple slow pumped system would work (with expansion tank etc of course) - another said it would not. Any views?
There should be a lock-out for the boiler. The normal way is not to have a TRV in one room and to put a room thermostat in there. The boiler will then be turned off completely.
I have a natural gas Aga, although don't use it for hot water.
With a gravity arrangement, the heat transfer is relatively slow. You don't say which fuel type that you have on the Aga, but the NG one has a maximum input of around 5kW. My concern would be that pumping the circuit would result in greater heat transfer rate than gravity and that the heat in the cooker store would then be depleted.
You could call Aga-Rayburn's technical support in Telford. I have found them pretty good.
The Aga is a great cooker, but if you have an alternative means other than electricity to heat the water, then that would be better. You could then go for a fast recovery cylinder which could take substantially more heat transfer.
Interesting responses thank you. Giving Aga a call sounds a great idea and I will do that. The pumped system will need to be turned right down so as not to exceed the modest heat output capability of the Aga which is oil by the way. I don't really want to run a 240,000 BTU boiler just to heat a water cylinder in summer. The boiler will feed something like 28 radiators so the prospect of all being shut down sounds unlikely - a no-flow switch closing down the boiler sounds much more sensible than a room thermostat in one room.
This probably wouldn't be too bad if a fast recovery cylinder is used. These are able to take around 30kW of heat from a boiler, and this is a 57kW boiler, so the cycling would not be too bad.
I am not sure that this would work very well. TRVs tend to reduce flow rather than cutting off completely unless the radiators are oversized for the conditions. In effect, this would result in flow continuing and the boiler cycling. By monitoring the temperature in the room, the cycling period of the boiler will be much longer because the room will cool slightly before the room thermostat signals heat needed again.
It's difficult to say without trying it though. You could start with the flow switch idea, putting a valve in line with the switch and another bypassing this valve and the switch so that you can adjust the flow rate through the switch and hence the sensitivity of the whole thing.
If it doesn't work and a room stat is needed, you could use a wireless one if you are bothered about the wiring. Initially this could be just placed in the room that you think should be the monitored one and the TRV full opened to disable its operation.
Indeed. I love my Rayburn, but it is turned off in the summer. I have an immersion heater which I can use, and the open fire in the living room (which is lit on coolish evenings) also heats water via the back boiler.
Well I run a 10KW boiler in sumnmer just to heat the water.
Its very cheap as it comes on about once or twioce a day for 5-10 minutes, and it means I can switch the aga off, which is mandatory in the summer otherwise it gets insufferably hot..
Not at all - I only know one person who switches theirs off! It depends on the architecture, windows and all sorts of things. the last thing one needs is a second cooker in the kitchen for when the Aga is off.
If your Aga heats water for the radiators/HW circuit continuously then the standard system (as descriped by TNP and Andy H) is not applicable, since the room stat cannot turn off the heat source (though it could operate the circulating pump). OTOH if your Aga has a separate heating boiler inside it (I don't know if Agas have this arrangement but I know that some Aga-like ranges do) then you should treat it like a normal CH boiler with a room stat arrangement.
Thermostatic radiator valves are a bodge. They use a thermostat fitted to attempt to limit the amount of boiler cycling that is need for the radiator valves to work.
The boiler has no way of knowing if any radiator needs heat ( other than the one in the room with the thermostat) so expect to waste a lot of energy compared to a system with individual room stats and motorised valves.
Its odd that the government thinks my 84% efficient boiler with individual stats and valves is less efficient than a condensing boiler with no proper control system. Maybe it needs some new advisors rather than the trade bodies it listens too.
To answer some confusion, the room stat etc would be on the boiler heating system - not the Aga.
At present we have two 110,000 boilers on two separate heating circuits and I want to rationalise with a single circuit and efficient modern boilers - we have a rambling Victorian place with 28 radiators. Both installers I have spoken to think we will need a boiler of up to 240,000 BTU capacity.
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Ah so IMHO perhaps what you should think about is a large hot water cylinder with two indirect coils. One fed from the Aga output and one fed from the heating system. During especially hot weather an immersion heater might be a useful extra also. In this way the Aga could heat the water in the cylinder with its slow but useable heat, The main heating system could under time/temperature control supply any additional requirement and you have the option of an immersion if and when needed. If the cylinder is sized appropriately your Aga should be able to look after all your needs except under occasional heavy demand periods. I'm surprised by the loading you suggest for the house even if it is rambling. Have you done any calcs or tried a heatloss program yourself? I have done a fair amount of work on a house which did have a 210,000 BTU boiler installed by others but it was never running for any appreciable length of time before its stat was satisfied. The house pipework was left over from a coke boiler and under the ground floor was in 4" Cast iron pipe, reducing to 3" & 2" branches around the (three) floors and serving big old cast iron school type rads. The house was bloody huge and could have been a stately home if out in the country rather than in a town. Draining down was an all day job as was filling up again so the boiler may have been deliberately (grossly) oversized simply to speed up the time taken to raise the water temp from cold to working. I think the old pile would have benefitted vastly from repiping to seperate the floors into independent controlled zones with smaller pipe and new rads to reduce volume and speed up the response times but client (as usual in these cases) wasn't interested in changing
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