Room losing heat fast

Andy499

So today I managed to get my office room up to 16.5 degrees which is what my thermostat is set at, which lives in my office room.

the rest of the house was… meh… living room (door closed, 2 people in there) was warm enough, kitchen was cold, hallway and landing cold, bathroom ok, bedrooms ok.

but as soon as my temp hit 16.5 the heating shut off and within 2 minutes it drops to 16.4 so heating comes on again, takes 10 mins to get it back to 16.5 and then goes off again. Repeats…

now it’s off for the night, but I have lost 1.5 degrees in that room already (1 hour). There are no draughts, blinds are closed, door is closed.

loft is insulated (not amazingly but around 6-8 inches)

im testing a “low and slow” heating approach so my flow temp on the boiler is only at 54-58 degrees. 

can anyone advise what I should do? Or should I just go back to heating the house for 2 hours a day? Once in the morning from about 11 degrees and once at night from around 13?

thanks

Lorian

If you are able increase the hysteresis on the thermostat to at least 0.5c to stop the short cycling. But because if the cold snap you are really facing increasing  your thermostat temperature and boiler flow temp and of course the extra cost.

FreeBear

Lorian said: If you are able increase the hysteresis on the thermostat to at least 0.5c to stop the short cycling.

If the boiler/thermostat supports modulation, enable it - The boiler will still run, but at a much lower level and hopefully provide enough heat to counter the heat loss.

markin

The important thing is what is the gas usage so far on the test?

If too many rads around the house are too low could the boiler actually be hitting its temp quickly and not being shut off by the stat, if you have a thermonitor in the room it could be + - up to 1 - 1.5c

tacpot12

I think the problem is the hysteris on your thermostat. The room is not losing heat that fast. We've got out lounge at 17C during the day and have the heating set to go off at 8:30pm. By 10:30 we are down to 15C, so we've lost 2C in 2 hrs. Your room is losing heat a bit faster, but I bet it is smaller than our lounge, so has more surface area to lose heat through relative to its volume. The room probably has less thermal mass than our lounge which has solid brick walls on three sides. e.g. if its internal walls are timber stud with plasterboard, this is going to lose heat more quickly than solid brick/plaster wall. Loses will be greater if the rooms on the other side of the walls are lower than 16.5C.

Ideally, your thermostat should have a hysteris of about 1-1.5C, so that the boiler is off for about 40 minutes to an hour once the office room has reached 16.5C. So the room will fluctuate between 15/15.5 and 16.5C. I can guarantee that  you won't be able to tell the difference, unless you look at the thermostat. 

Also your thermostat should be located in the room that is the hardest to heat (you might interpret this statement as meaning the room that has the smallest radiator compared to the actual heat loss of the room - an oversized radiator in a room with a high heat loss like a hallway might mean that the hallway is not the hardest room to heat). Ideally, you want the thermostat to turn off the boiler and pump ONLY when ALL the other rooms are up to temperature. The TRVs in the other rooms should prevent those rooms from getting any warmer than you want them.

You could turn your thermostat up to, say 21C, and use the TRV on the radiator in the office room to limit the temperature in the room to 16.5C, then the boiler would never be turned off by the thermostat. The temperature in all ahe other rooms would still be controlled by the TRVs. With the controls set this way, the boiler & pump will basically be running all the time. However, the rooms are all losing some heat and this heat needs to be replaced by the boiler. The TRVs adjust the flow through the radiators so that the leat loss from the room is exactly met by the amount of heat that the radiator needs to keep the room at the set temperature (despite being simple devices, they work in a very clever way). They can only do this to a point though - if the room needs more heat than the radiator can provide for its size, then once the TRV is fully open it can do no more. Also, if the water in the heating system isn't very hot, even with the TRV fully open, it can't replace all the lost heat, but assuming radiators are sized correctly and the flow temperature on the boiler isn't turned down stupidly low (or you are thinking about a time when the system has just been turned on), TRVs can do a great job of extracting just the amount of heat needed to replace that lost from the room.

The effect of all the TRVs doing their thing is that the water flowing back to the boiler is that the temperature of the water returning back to the boiler is going to eventually settle down to a temperature that reflects the amount of heat being lost from all the rooms. This temperature will be different on a cool day vs. a cold day. The water returning to the boiler on a cool day might be 60C and on a very cold day it might be 45C. The boiler will be set to produce water at a certain temperature (called the flow temperature), say 70C. A modulating boiler will automatically adjust the gas valve and fan speed that that the burner raises the temperature of the returning water to exactly the flow temperature that is set. (You can also get pumps that modulate to reduce the flow rate if there less demand from the radiators - the more the TRVs shut down the flow because the room is at the right temperature, the more restriction is felt by the pump so it reduces its speed) So on cold days, the boiler will use more gas and run the fan faster than on cool days. A boiler that cannot modulate can only produce a fixed amount of heat, and so they use a on/off cycle to heat the water to an average flow temperature of what ever is set as the flow temperature . Again the same concept of thermostat hysterisis comes into play - if the thermostat on a non-modulating boiler is set for an average flow temperature of 70C, the boiler might fire until the water is upto 75C, and then it will turn off, but the pump will keep the water circulating, the TRVs will take heat out of the water and return it at a lower temperature. When this temperature is below say 65C, the boiler will fire again to raise the returning water temperature until it is at 75C (so the boiler might run for 10 minutes or so) and then will turn off again, and the cycle repeats so that the boiler delivers an AVERAGE flow temperature of 70C. The hysterisis on the boiler's thermostat is 10C (75C- 65C).   

On cooler days, a non-modulating boiler will spend more time off that it will on cold days because the radiators are taking more heat out of the water so the boiler has to run for longer to get back to 75C before it can switch off for a rest. The boiler can also be turned off by a room stat reaching its set-point, but above I have tried to describe how thinkg work when the room stat is set to a temperature that is higher than the TRV in the room is set for - assuming you have a TRV on the radiator in the room with the Thermostat. We have such a setup. Our thermostat is in the hallway (which is the hardest room to heat), but there is also TRV on the radiator in the hallway - the thermostat was only installed a couple of years ago when our old boiler was replaced.  So although the boiler and pump are "On" all the time, seen from the perspective of the room thermostat, the boiler and pump are actually either being turned on and off by the thermostat within the boiler to produce an average flow temperature, or being modulated to produce the actual flow temperature required. (Our boiler is a modulating one). 

I should also mention that I'm a curious householder, not a heating engineer, and so the above is just what I think I know about heating systems. Hope it helps.