Energy myth-busting: Is it cheaper to have heating on all day?

david1946

Sued1951 said:

I have warm air central heating, which I believe is more efficient as it sucks in the air, heats it up and chucks it back out again. My house can warm up in 5 minutes. I dont heat water to heat radiator to heat air so the whole process is quicker. I also have a direct from the mains water heater so that means no tanks and I only heat the water I need. My energy bills are very low as my house is very well insulated including cavity wall insulation. I use very little electricity as I have solar panels. I dont think that there is anything else I could do to conserve energy and keep my bills down apart from having storage batteries for my solar. As these are very expensive I am not sure that they would be cost effective enough for the investment needed.

I used to have warm air heating and it may seem efficient as it heats the air direct but how much heat are you losing due to the needed ventilation for the gas burner?

I replaced my gas warm air heating with a combi and radiators and my yearly average gas useage dropped from 24,000 kWh a year to 14,000 kWh a year.

You also use about 1kWh of electricity less a day because there is no fan.

Cardew

4caster said:

Correction: "economical", not "ecumenical". God forgive me!

I have done my Son, but three Hail Marys would be appropriate!

rp1974

Blasphemy,such Godless times. .

orrery

4caster said:

The trouble with having a "main thermostat" is that it will override the radiator thermostats in all other rooms. I don't want the radiators in the bathroom or dining room to go cold just because the lounge has attained the temperature set on the main thermostat. The whole point of having adjustable thermostatic radiators in each room is to heat each room to the temperature required for that room. An overriding main thermostat thwarts that intention.

It is indeed a very slight problem, but not having a main thermostat gives you a bigger problem. As the rooms come up to temperature the radiator stats close down, the water flow is restricted and the boiler has to reduce power. This means that the return temperature to the boiler will steadily increase and the boiler will cease to be condensing and it's efficiency goes to pot, and some will end up going over-temperature and cycling on and off. It also means that the boiler will fire up on warmer days when it just isn't necessary. Clever 'smart' thermostats will shut down the heating when you leave the house, suspend the heating when sun is expected, bring the heating back on as you approach home, allow you to set it remotely, shut off the heating if someone has the front door open, pull forward the start time if the temperature is very cold etc etc. They can also run in 'proportional' mode as you approach the set temperature (say, within 1 degree C) - this means that the system will turn on and off by variable time periods which helps to alleviate the problem you highlight and helps keep the boiler in condensing mode. Certainly, the lounge wouldn't be a good choice for the main stat.

You then need the system to be properly balanced - where the isolation valve (the one on the other end of the rad from the stat) is turned to reduce flow on radiators that come up to temperature first, and force flow to other radiators that may struggle.

Once that is sorted, with a decent smart controller, you can just get on with your life without having any concern for the heating - it just sorts itself out, and saves money in the process.

anothergrumpyoldman

I don't see the benefit of thermostatic radiator valves (TRV).  For one thing they are too close to a heat source (the radiator), they are expensive to buy and fit and, more importantly, they aren't necessary.  When the primary (wall) thermostat is calling for heat the TRV will do it's job because hot water is being pumped around the system.  However, when the primary thermostat is not is not calling for heat no water is being circulated so, even if a TRV thinks the room it's in is too cold, no heating will take place.  The best approach overall is to place the wall thermostat away from a heat source and balance the other radiators using standard manual control valves to give the preferred temperature in the other rooms.  This system will make the best job of providing a steady temperature for the times the boiler is running, but it does take a bit if time and effort.

Cardew

anothergrumpyoldman said:

I don't see the benefit of thermostatic radiator valves (TRV).  For one thing they are too close to a heat source (the radiator), they are expensive to buy and fit and, more importantly, they aren't necessary.  When the primary (wall) thermostat is calling for heat the TRV will do it's job because hot water is being pumped around the system.  However, when the primary thermostat is not is not calling for heat no water is being circulated so, even if a TRV thinks the room it's in is too cold, no heating will take place.  The best approach overall is to place the wall thermostat away from a heat source and balance the other radiators using standard manual control valves to give the preferred temperature in the other rooms.  This system will make the best job of providing a steady temperature for the times the boiler is running, but it does take a bit if time and effort.

Welcome to the forum.

Whilst I would agree that TRVs have their limitations, and you give a good example of when a TRV thinks the room is too cold when the primary thermostat is not calling for heat, I do not agree with other points in your post. More importantly neither do the 'authorities' as TRVs are mandatory on all new installations.

Using the standard manual control radiator valves to control the temperature in a room is not a solution. When that valve is open the water, at the temperature set by the boiler, will enter the radiator. The radiator will get up full temperature, as long as the pump is running. The length of time the pump is running depends on the primary thermostat. So on a cold day when the pump is running for a long time the other rooms will get up to full temperature regardless of how little the standard valve is open.

Of course you could walk around the house day and night switching on/off the standard valves to control the temperature, but that is exactly what a TRV does automatically.

orrery

anothergrumpyoldman said:

I don't see the benefit of thermostatic radiator valves (TRV).  For one thing they are too close to a heat source (the radiator), they are expensive to buy and fit and, more importantly, they aren't necessary.  When the primary (wall) thermostat is calling for heat the TRV will do it's job because hot water is being pumped around the system.  However, when the primary thermostat is not is not calling for heat no water is being circulated so....

Yes, in some sort of perfect world, that makes sense. But ...

Situations change in each room - I might light the log burner, the window may be left open, the sun may well be shining on one side of the house, heating all the rooms on that side. My bedroom TRVs shut down early, as there is always heat coming upstairs.

TRVs of quite 'soft' in operation. As they approach the set-point, they start to restrict water flow so the radiator becomes warm instead of hot, and in that way they tend to provide an automatic balancing of the system - rads that are well supplied start to restrict early and water is forced to remote rads which then do their job.

In the case you highlight, the TRV will open more in cold room when the main stat shuts the system down, so it gets the lions share when the system comes back on. If the central stat is smart, it will be running the system in proportional mode most of the time, so each rad will get a regular burst of heat from the boiler, the amount required will be moderated by the TRV. It works, and it works well.

Talldave

There's a significant difference between a system with "wall" thermostat and manual TRVs and a system with smart TRVs. In the latter case, any TRV can call for heat against its own temperature schedule and any form of overall thermostat is unnecessary. 

The cost of the two alternatives reflects the level of cleverness and customisation possible.  With the fully smart system you can keep bedrooms warm at night whilst letting other areas cool and then reverse the focus of heat to the living areas during the day.

richardc1983

Talldave said:

There's a significant difference between a system with "wall" thermostat and manual TRVs and a system with smart TRVs. In the latter case, any TRV can call for heat against its own temperature schedule and any form of overall thermostat is unnecessary. 

The cost of the two alternatives reflects the level of cleverness and customisation possible.  With the fully smart system you can keep bedrooms warm at night whilst letting other areas cool and then reverse the focus of heat to the living areas during the day.

How does that work if all the rooms are up to temp what will tell the boiler to turn off and the pump to stop if there is no main thermostat?

matelodave

richardc1983 said:

Talldave said:

There's a significant difference between a system with "wall" thermostat and manual TRVs and a system with smart TRVs. In the latter case, any TRV can call for heat against its own temperature schedule and any form of overall thermostat is unnecessary. 

The cost of the two alternatives reflects the level of cleverness and customisation possible.  With the fully smart system you can keep bedrooms warm at night whilst letting other areas cool and then reverse the focus of heat to the living areas during the day.

How does that work if all the rooms are up to temp what will tell the boiler to turn off and the pump to stop if there is no main thermostat?

It sort of relies on the return water being hot enough to shut the boiler down and then leaving it cycling away all day keeping hot just in case something wants some heat in which case the boiler has to control the pump.
I guess that a proper smart system would also have a boiler control to enable the boiler when something calls for heat and shuts it down when it's been satisfied. A basic electronic RAD valve wont do that.