Heat curve advice

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paulmapp8306

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Looking for some advice on heat curve setup.  Only recently installed a new system with a weather compensatory, but my room temps are all over the place.

As I understand heat curves (after some internet searching),  the higher the curve, the hotter the water in the heating system is for any given outside temperature - and the lower the curve the cooler the heating water is.

From my understanding of heating/thermo dynamics (though Im an electronics tech not a plumber/heating engineer) - a high curve will result in hot radiators.  This will raise the room/house temp quickly from a base point, which n the face of it is a good thing.  BUT Im thining that it means once he "set" temp is reached the overshoot is greater than a low heating curve.  Once the boiler stops heating - the hot water in the rads are still heating up the rooms.  Because there hot they still heat quite quickly, and will take longer to cool to room temp and below.  This means the room temp will keep going up for a while.

A low heat curve will result in a muck more stable room temp once the "set" temp is reached - because once the temp is reached and the boiler shuts off, he rads are cooler than with a high heat curve.  The room still heats up but more slowly, and the rads cool quicker to room.below room temp.  This should (in theory) result in a more stable room temp as the room temp wont go as high before the rads stop having an affect.  The down side is it takes longer to reach the room temp from a  lower than "set" temp (say set back temp).

Im guessing that the "ideal" is as low a heat curve as you can get - while still getting a cold room up to temp in a reasonable time.  Not only go you get the more stable room temps - but use less gas getting there.

Is that about right?  or am I all wrong here.  The installer set curve is 2.4 - but despite setting the room temp to 21.5 Im often getting to 24 deg before the rads cool and the room temp falls again.  That makes the 21/21.5 when the rads turn back on actually feel cool.   Im guessing lowering the heat curve will work better (Im trying 1.5 for tomorrow as a start point).

So - am I right be to thinking this way - or do I have it totally wrong.  If wrong - how should I be setting the curve?

Thanks

 
Well your heat curve is set too high. Personally I am very skeptical.  Unless you have a really old poorly insulated house, you should not need anything other than a fixed temperature and a room thermostat.

 
Thinking further - IF I have the theory right - the ideal heat curve once you reach you "set" temperature will be only just higher enough for the rads to put out the same heat the room/house looses thus keeping the temp stable.  This will obviously vary, depending on room/house size, drafts, how much glass there is - single/double/tripple glazing etc as well as how many rads you have, and what there heat output is.  Probably why there is no advice on "x" is the ideal heat curve.

Obviously you can have that heat curve, unless your heating is on 24 hours a day, or youll never  raise the room temp from the set back/overnight temperature.

Seems ideally a heating system would have 2 heat curves.  a "high" one that kicks in when the heating comes on and the room temp is down near/at/below the set back temp - and a second "low" one for when you reach the "set" room temp.  Then either have the boiler switch between the 2 when you get close "say 1 deg below" the "set " temp OR for the curve to gradually lessen from max to min as you approach the set temp.   Not sure any exist, and certainly dont think mine has that (it has an adaptive curve - but I think thats more an intelligent "learning" of the single curve that best suits the house rather than altering the curve dynamically).

So - I guess its trial and error - but Im aiming for the lowest heat curve that has the house up to temperature when we need it (so say the heating comes on an hour before we get up - it has to reach the set temp from set back in that hour) but no higher (or were burning too much gas, and going over temperature with wider swings).

Please put me right if Ive totally got this wrong - but please if Im right, let me know so I dont keep "fiddling" trying to get things right...when Im doing it wrong.

Thanks.

Well your heat curve is set too high. Personally I am very skeptical.  Unless you have a really old poorly insulated house, you should not need anything other than a fixed temperature and a room thermostat.


I have the room thermostat, but I dont think I can just set a "fixed" temp as the whole system works with the outside stat as well.

 
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Its a Vaillant Ecotec 418 (normal open vent boiler), a VRC700f control, VRC20 outdoor thermostat, and VR70 wiring centre.

 

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