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

Cardew

coey said:

Don't believe in thermostats , only got one as legally obliged to. Use timer [ 8.30-10.30 / 16.30-22.30 ] plus manual interventions as required. central thermostat fitted in hall and set to 25 [ which it will never reach nor do i want it to reach ] ALL rooms fitted with Thermostatic radiator valves which control desired temperature in each individual room ONLY when that particular room needs heating......Can't believe TRV's have not been mentioned more , in my opinion mandatory fitting of TRV's should come way before any ridiculous ideas like heat pumps.

TRV's have been mandatory on all new installations for years.

Yet again this thread, like all previous threads on this subject, has morphed into posters describing their method of controlling their heating,

 

QrizB

coey said:

Don't believe in thermostats

Fortunately, thermostats (like gravity but unlike fairies) work whether you believe in them or not.

JSHarris

coey said:

Can't believe TRV's have not been mentioned more , in my opinion mandatory fitting of TRV's should come way before any ridiculous ideas like heat pumps.

What's "ridiculous" About heat pumps, out of interest?

We heat our 1,400 square foot detached home with one.  Fantastically cheap to run, the heating part of our annual electricity bill is around £200.  Our total electricity bill for the year is about £750, but that includes heating our hot water (which is directly electrically heated via a thermal battery), cooking, lighting, charging my EV, etc.  Installing the heat pump was far and away the very best decision I've made and its performance has exceeded my expectations.  I'd heard all the horror stories about them not working in cold weather, being noisy, etc, but that's complete BS.  Our heat pump has worked fine when we've had cold weather well below freezing, it never misses a beat.  It's also so quiet that I've had people stand next to it and not realise it's been running.  Best of all was that it was very easy to install (I did it myself, took less than a day and I've never fitted one before) and it wasn't expensive (I bought it from a wholesaler, cost under £1,000 delivered).

FreeBear

coey said:in my opinion mandatory fitting of TRV's should come way before any ridiculous ideas like heat pumps.

TRVs are a requirement in Building Regulations when fitting a new boiler (or heat pump).

markin

Reed_Richards said:

I hope nobody would dispute that, @Qyburn.  But what has kept this thread running and running is the suggestion that because of the way some heat sources operate, the extra energy used to bring the house back up to temperature is more than the energy saved in allowing it to cool.  Gas boilers and heat pumps tend to work less efficiently when working harder so this is indeed a theoretical possibility, and there is a paucity of actual evidence one way or the other.

The is a very clear US DOE study on air/air heatpumps in new identical homes that shows that people that set constant 24/7 temps saved almost 50%, from memory Vs the people that used on/off.

.........

This thread has been bumped almost every year from 2012.

...

victor2

markin said:

Reed_Richards said:

I hope nobody would dispute that, @Qyburn.  But what has kept this thread running and running is the suggestion that because of the way some heat sources operate, the extra energy used to bring the house back up to temperature is more than the energy saved in allowing it to cool.  Gas boilers and heat pumps tend to work less efficiently when working harder so this is indeed a theoretical possibility, and there is a paucity of actual evidence one way or the other.

The is a very clear US DOE study on air/air heatpumps in new identical homes that shows that people that set constant 24/7 temps saved almost 50%, from memory Vs the people that used on/off.

.........

This thread has been bumped almost every year from 2012.

But that then raises the question (and not for the first time!), when is having it on 24/7 more costly. If you're going away for the weekend, do you leave your heatpump on to save money?

This thread has indeed been like a phoenix rising from the ashes annually when it starts to get cold! Didn't think it was going to appear this year, but it hasn't let us down.

QrizB

Here is an extract from the report that @markin refers to:

https://www.energy.gov/eere/buildings/articles/building-america-technology-solutions-new-and-existing-homes-long-term

The extract states:

Most of the test houses were run using a constant set point; however, one homeowner controlled the MSHP by turning the unit on and off in response to perceived comfort and occupancy of a given space (first or second floor).

So the on-off house (only one, of 8) wasn't controlled by a thermostat; it was switched manually by the occupant based on their subjective opinion of the temperature being too hot or too cold.

I'm not at all convinced that this can be applied to the general case of eg.

victor2 said:

 If you're going away for the weekend, do you leave your heatpump on to save money?

JSHarris

We don't really have much choice, as the house thermal time constant for a 1°C indoor temperature change, for a 12°C inside to outside temperature differential, is a bit over 48 hours.  Means that it's not practical to turn the heat pump off, or even down, if we're away for a few days.  Given that it's pretty cheap to run (it draws between 600W and 800W when running, perhaps 1,100W for the first five to ten minutes when it starts up) and it only comes on at most for 7 hours overnight in very cold weather (it's normally only on for three or four hours, the cost of having it on on the very few occasions when I could turn it off isn't really worth worrying about.  A typical winter day's heating costs less than 50p, and that seems a small price to pay to come back to a warm and comfortable home.

QrizB

JSHarris said:

We don't really have much choice, as the house thermal time constant for a 1°C indoor temperature change, for a 12°C inside to outside temperature differential, is a bit over 48 hours.  Means that it's not practical to turn the heat pump off, or even down, if we're away for a few days.  Given that it's pretty cheap to run (it draws between 600W and 800W when running, perhaps 1,100W for the first five to ten minutes when it starts up) and it only comes on at most for 7 hours overnight in very cold weather (it's normally only on for three or four hours, the cost of having it on on the very few occasions when I could turn it off isn't really worth worrying about.  A typical winter day's heating costs less than 50p, and that seems a small price to pay to come back to a warm and comfortable home.

"I have a home that only cools by 1C every 2 days and only needs 2-3kWh a day to keep warm. I don't turn my heating off when I go away for the weekend because it's cheap to run."

Sorry but I'm not sure that really advances the dissussion.

JSHarris

QrizB said:

JSHarris said:

We don't really have much choice, as the house thermal time constant for a 1°C indoor temperature change, for a 12°C inside to outside temperature differential, is a bit over 48 hours.  Means that it's not practical to turn the heat pump off, or even down, if we're away for a few days.  Given that it's pretty cheap to run (it draws between 600W and 800W when running, perhaps 1,100W for the first five to ten minutes when it starts up) and it only comes on at most for 7 hours overnight in very cold weather (it's normally only on for three or four hours, the cost of having it on on the very few occasions when I could turn it off isn't really worth worrying about.  A typical winter day's heating costs less than 50p, and that seems a small price to pay to come back to a warm and comfortable home.

"I have a home that only cools by 1C every 2 days and only needs 2-3kWh a day to keep warm. I don't turn my heating off when I go away for the weekend because it's cheap to run."

Sorry but I'm not sure that really advances the dissussion.

In my view it does, as the thermal time constant seem to be a critical consideration.  If your home takes a couple of days to warm up after having the heating turned off for a time, then that makes for a pretty uncomfortable time when you get home, turn the heating on and then wait around in a chilly home for the rooms to become warm (which is a direct consequence of having a long thermal time constant).

We can mitigate this to some degree by opting to use additional heating, like fan heaters that warm the air up quickly, but they would be very costly to run, and would cost a great deal more than just leaving the heating on and keeping the house warm when we're not at home.