Thermostatic Rad Valves V Room Stat


Postby jp1 » Thu Dec 13, 2007 7:57 pm

I have a situation where I have a very cold conservatory with a single rad. controlled by a TRV. My heating system is controlled overall by a room stat at the bottom of the stairs in a small hall that heats up quickly so cuts off before enough heat gets into the conservatory.

If I change my heating system over to TRV's rather than a room stat. does anyone know whether it is more or less efficient than control by a standard room stat.?
Would I remove the room stat. or just set it to max and allow the TRV's to do their job?
I've been told I would need to leave one radiator with a standard rad valve, possibly the bathroom. Is this true and if so what would control this?
Any advice greatly appreciated.
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Postby htg engineer » Thu Dec 13, 2007 9:06 pm

have you tried turning your room thermostat to max ? a conservatory in this weather will never get warm, your boiler will stay on continously as alot of heat will be lost and it will cost alot in gas. How about re-positioning the room stat ?

My conservatory has no radiators, just heavy curtains between living room and conservatory, the conservatory is freezing but the living room is warm. I also don't have a room stat, I use the boiler stat to control the temperature, it is set to max at the moment.
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Postby marrtin » Thu Dec 13, 2007 9:09 pm

There needs to be at least one rad left without a TRV so that there will always be water circulating which is required to protect the boiler and pump. Ususally this is where the room stat is otherwise it may never reach temperature to switch off the heat.

It is universally agreed that thermostats are required to maintain a balanced and efficient system. In fact, hew combi's are fitted without a timer and are controlled by a room stat!

The point is do you want the heat on in July? Ok, so you say you would turn it off. So I say what do you do whilst away in Spain for a fortnight this Christmas? Leave it on or turn it off?

How does the rest of the house feel? warm or cold? If the temps are about right, moving the stat to the conservatory will just make the rest of the house warmer. The problem probably is the rad there is too small for the type of room.
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Postby robertw63 » Tue Dec 18, 2007 12:12 pm

The problem is that the heat losses from the conservatory are probably much greater than those from other rooms and also that the radiator in the conservatory is probably too small (as most of them are!).

Unless your conservatory is very new is will not conform to the latest U values. If you do as you suggest it will still never get hot, the repositioned thermostat will never be satisfied and your house will cook.

What you really need is a larger radiator in the conservatory. In a typical conservatory (which has 3 outside walls and no loft insulation!) you might need a radiator up to 3 times the size that a similar sized bedroom might need. This isn't really practical so you have to settle for a lower temperature I'm afraid.
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Postby DONFRAMAC » Wed Dec 19, 2007 1:18 am

A month ago I saw a new conservatory, which was glazed to the best you could expect in a living-room, ie 12 mm air-gap, with heat-reflective Pilkington K glass. I expect the roofing was triple- layer polycarbonate panels.
Re-glazing to these standards is a simple upgrade ; --- my sister had it done 3 years ago, and she had the ceiling lowered, using a metal frame and square panels and downlighters.
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Postby ericmark » Sat Dec 29, 2007 5:10 am

Old boilers turned off and on as the room thermostat controlled it. But modern boilers measure the temperature of the return water and adjust the boiler to suit the demand. Fitting thermostatic radiators valves to an old system can never replace the room thermostat but on a new system with anti cycle software in the electronic control then the thermostat would be better placed outside so the system shuts down in the summer. Really a manual off switch for summer is all that is required. A room thermostat will only mess it all up. But the setting of flow rates is now very important and the use of fan assisted radiators really messes up the system as with these the water is not turned off when room becomes warm only the fan so the returning water gets hotter and turns down the boiler before the rest of the house is warm.
If you look at a modern boiler it has a range output like 8 to 25Kw where old ones had single fixed output.
If you fit thermostatic radiator valves to old system you must have one radiator without but new system has built in bypass in boiler. Since the old one switches off on output water not return it can take quite some time to reset and switch back on again with new system if set up right in winter it never turns off it only reduces output.
With the new system when out of the house if the system is turned off with a timer then if one or more radiators are left full on and not trimmed in correctly it can take a very long time to heat the house as the few radiators with too much flow turn the boiler output down but once everything is warm and the thermostatic valves start to work then it works very well so often one finds people never turn it off because it takes so long to re-heat being unaware why.
Using room thermostats with built in timers with not work of course with new system as it only controls one room.
So thermostatic radiator valves v Room thermostat all depends on the type of boiler fitted.
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