Combi Boiler Thermostat Use

robcole86

Morning!

I've read a lot of different post regarding combi boiler use and plenty regarding energy saving but none exactly fit what I wanted to ask so here goes.

I usually get home from work about 6pm and my partner about 5pm. We set the digital thermostat to come on at about 4:30,sometimes earlier in the winter to about 21 degrees. My normal use then is to leave that on that setting for the remainder of the evening, never turning the heating off properly until we go to bed about 9:30-10ish.

I understand that would mean the heating will go off an on as required but I want to ask it is more efficient or cheaper to say let the room get to temperature then turn the heating off until back down to a temperature whereby it is cold again eg start at 21 let it get to 19 before turning it back on? Or is it simply cheaper to use the thermostat for long periods as I do set at 21?

Thanks a lot
Rob

r2015

then turn the heating off until back down to a temperature whereby it is cold again eg start at 21 let it get to 19 before turning it back on

That is what the thermostat does.

robcole86

Well, not quite as in the thermostat will be at say 21 and if it even drops by half a degree the boiler will fire up ensuring it stays at 21. So either I do that OR let it drop by a significant amount before turning on again.... There's a not a huge difference here I know I was just wondering whether it'd make a difference to energy usage etc

r2015

If you want your temperature to vary by 3 deg then do it manually, I don't see the point.

thozza

robcole86 wrote: »

Well, not quite as in the thermostat will be at say 21 and if it even drops by half a degree the boiler will fire up ensuring it stays at 21. So either I do that OR let it drop by a significant amount before turning on again.... There's a not a huge difference here I know I was just wondering whether it'd make a difference to energy usage etc

Electronic (room) thermostats are designed to cycle the boiler to achieve the desired set temperature. Most have have a cycle rate adjustment built into them, this sets the thermostat to only turn on and off a certain number of times an hour (say 3-5), they also have a setting which controls the minimum on/off time and also the set temperature difference, usually around 1.5 deg C, Honeywell explain thus:

A TPI room thermostat works by continuously measuring the room temperature and calculating a difference between measured and target temperature. When the difference is greater than 1.5 degrees C (known as outside proportional band) it fires the boiler continuously. When the room temperature gets within 1.5 degrees C of the set point you have chosen on your room thermostat, the TPI software in the thermostat comes into action. It performs a series of calculations where it calculates how long the boiler needs to be fired to reach and maintain the set temperature. The calculation is based on the previously learnt characteristics of
the room in which the controller is placed and the current measured temperature. This ‘smart’ firing of the boiler will mean that the boiler is fired just long enough to achieve the set temperature and no longer, thus increasing energy efficiency.

Electromechanical thermostats operate on a similar 'bandwidth' principle, but are not capable of some of the more sophisticated control.

If your thermostat is calling for heat often, then switching off quickly, it would be worth checking it it is functioning correctly. It might be worth replacing it with a modern thermostat which should offer a higher level of efficiency and will require no manual intervention.

macman

The longer the boiler is running, the more gas it will burn. It takes a fixed amount of energy to heat the house by x degrees, everything else being equal.
A combi is no different to a conventional boiler in this respect.

C_Mababejive

#6 Agreed,,boiler fires,gas in burned,cost is incurred.

You could fit a more sophisticated programmable roomstat which has smart/anticipatory type capabilities but then your exiting RS might already be of this type. The real answer is to invest in cutting heat loss from your home.

Pincher

Condensing boiler are most efficient when recovering the heat from the combustion plume. This means continuous operation at low boiler output, so the return flow is low enough in temperature to pick up the residual heat from the plume.

Ideally, you want to have thick insulation, so the heat loss is minimal. The boiler is simply replacing the heat you are losing. Less loss, less heat needed.


What you want to do is easily done by having a programmer with a BOOST button. The timer should get the house/room up to 21 degrees from 16:30, then goes off say 18:00. From then on, you just stab the boost button if you sneeze. Psychologically soothing, because you think you are doing something, but ultimately pointless.

Cardew

If you prefer the temperature to be 21C then setting it to 19C will save money, but you will be less comfortable as it is not your preferred temperature.


On the other hand if you set it to 19C initially and let the thermostat, do its job, you will save gas and hence money.

robcole86

Thanks everyone, much appreciated #5 thozza is correct - I've read into my digital thermostat and it seems that the thermostat is simply anticipating the loss in heat over the next hour to be x therefore is coming on accordingly beforehand to ensure the temperature stays the same.

Thanks a lot
Rob

Pincher

robcole86 wrote: »

it seems that the thermostat is simply anticipating the loss in heat over the next hour to be x therefore is coming on accordingly beforehand to ensure the temperature stays the same.

The house is ALWAYS losing heat. The only problem is, a lot of boilers are over sized for the house, so it can only go down to say 10kW, when you are only losing heat at 5kW. So, there is no choice but to switch off, and then come back on again.