Is there a ball park figure for the %age increase in energy use for a typical residential property for every degree the internal temperature is increased above 20deg. C..
I realize there is a whole bunch of variables that will alter the answer but I am looking for a rough guide number.

I use a rule of thumb for heating energy use, one degree higher =5% extra 2 degrees 7 and three is close on 15% additional heating bill - on average when it is very cold outside costs can be higher

Note, heating energy as opposed to total energy use (I include most lighting energy in heating energy use)

My attempt to come up with the inverse of this - how the boiler run time varies with outdoor temperature and wind - for the rental house I'm now in:

https://edavies.me.uk/2021/02/heatreq2/

As I mentioned earlier, if you live near me then you need heating every day, whether incidental or deliberate, the proportion depending what base temperature you specified.

If I can insulate enough, I can reduce my non-incidental heating demand maybe even to 1000HDD, so then each degree of heating becomes more significant, as I mentioned.

If you live somewhere else, then you can adjust your base temperature and recalculate, as I mentioned, which will account for however many days you have when the average temperature is above 21degC. There are several other adjustments you can make for improving accuracy, like Ed has done, but I understand that isn't what PiH is looking for.

Thanks for the answers so far.

The story behind the question is that I have a tenant who has made the life style choice that in the winter he likes to sit in the lounge (and move around the house) in shorts and a tee shirt and for this he wants a temp. of 26 - 27 deg. My resources can't keep up with this ! I just don't have enough forest to sustain this rate of energy usage (all heating is done with wood), quite apart from what I would consider the ethical issues of squandering resources with the attendant pollution.

I can quantify the central heating which they want on evenings and over night (1800 to 0600) which last month amounted to 1450kWh but in addition to this there is a wood burning stove which is lit about 1400hrs when they come home from work and is run flat out until they go to bed about 2300hrs. The wood stove is close to impossible to quantify as wood is so variable, I just see the rapidly diminishing pile. The energy is charged for by a kWh meter for the CH and the WBS by volume of wood.

I would consider about 20degC to be a reasonable domestic temp. (our tourist regs. stipulate that property should be capable of heating to 20degC)The answer from Will implies a 12% increase in energy from 15 to 16 and the reply from Tony implies that a 3deg increase = +15% so putting those together running 6 - 7deg higher is probably going to use something around 30% to 40% more energy

Next question is - what to do about it !

Posted By: Peter_in_HungaryThe story behind the question is that I have a tenant who has made the life style choice that in the winter he likes to sit in the lounge (and move around the house) in shorts and a tee shirt and for this he wants a temp. of 26 - 27 deg. My resources can't keep up with this ! I just don't have enough forest to sustain this rate of energy usage (all heating is done with wood), quite apart from what I would consider the ethical issues of squandering resources with the attendant pollution.

I can quantify the central heating which they want on evenings and over night (1800 to 0600) which last month amounted to 1450kWh but in addition to this there is a wood burning stove which is lit about 1400hrs when they come home from work and is run flat out until they go to bed about 2300hrs. The wood stove is close to impossible to quantify as wood is so variable, I just see the rapidly diminishing pile. The energy is charged for by a kWh meter for the CH and the WBS by volume of wood.

I would consider about 20degC to be a reasonable domestic temp. (our tourist regs. stipulate that property should be capable of heating to 20degC)

What does your contract say? i.e. the lease? Does it make any promises about fuel supply, who and how much? Is the CH a wood-burning boiler or somesuch?

Assuming no legal problems, just tell him the maximum quantity of wood you are willing/able to supply. Perhaps advise him where he might be able to buy more.

<blockquote><cite>Posted By: Ed Davies</cite>My attempt to come up with the inverse of this - how the boiler run time varies with outdoor temperature and wind - for the rental house I'm now in:

<a href="https://edavies.me.uk/2021/02/heatreq2/" rel="nofollow">https://edavies.me.uk/2021/02/heatreq2/</a></blockquote>

I realise from your article that you are not happy with your 2019 heatreq equation, but just for interest I put a few figures together in an Excel spreadsheet and came up with a plot of heatreq vs wind speed for three typical winter scenarios where t = -5C, 0C and +5C and wind speeds from 0 to 25 m/s (plotted as mph equivalent). Intuitively the plots "feel" correct (no pun intended!) as there is an exponential effect with increasing wind speed. I'm not sure how to interpret the results as it surely cannot mean for example that at 0C and a wind speed of 55 mph the heat requirement to maintain an indoor temperature of approx 20C would be nearly 5 times as much as that required when there is no wind at all at the same exterior temperature?

As you can see from my last post our wood pellet consumption increases significantly when the external temperature gets down to around 0C, combined with a strong N/NE wind, so anecdotally at least there is a definite correlation.

Posted By: djh

Posted By: Peter_in_HungaryThe story behind the question is that I have a tenant who has made the life style choice that in the winter he likes to sit in the lounge (and move around the house) in shorts and a tee shirt and for this he wants a temp. of 26 - 27 deg. My resources can't keep up with this ! I just don't have enough forest to sustain this rate of energy usage (all heating is done with wood), quite apart from what I would consider the ethical issues of squandering resources with the attendant pollution.

I can quantify the central heating which they want on evenings and over night (1800 to 0600) which last month amounted to 1450kWh but in addition to this there is a wood burning stove which is lit about 1400hrs when they come home from work and is run flat out until they go to bed about 2300hrs. The wood stove is close to impossible to quantify as wood is so variable, I just see the rapidly diminishing pile. The energy is charged for by a kWh meter for the CH and the WBS by volume of wood.

I would consider about 20degC to be a reasonable domestic temp. (our tourist regs. stipulate that property should be capable of heating to 20degC)

What does your contract say? i.e. the lease? Does it make any promises about fuel supply, who and how much? Is the CH a wood-burning boiler or somesuch?

Assuming no legal problems, just tell him the maximum quantity of wood you are willing/able to supply. Perhaps advise him where he might be able to buy more.

The contract gives the price / kWh for the CH which is a wood burning boiler with a TS where the kWh is measured by an inline kWh meter and the wood for the stove is priced / m3. There are no amounts of fuel specified.

Reading through the WBS manual it would appear that the amount of wood being used puts the stove outside of the operating specifications. I suspect they are running the stove with the door wedged open to get a hotter burn (I caught them at this once on a casual visit and mentioned it but without barging in it is now difficult to prove) However the amount of wood used , putting the stove out of spec. would mean that they are failing in their duty of care of the property which would be a breach.

I will be telling them that the amount of wood they are using is beyond my forest management plan and they will have to source their own supply.

The attitude of heating the house to shorts and tee shirt temps. in the winter goes against my ethics. But at least they don't smoke in the house, (also in the contract) but they put on a dressing gown to stand outside to have a fag.

<blockquote><cite>Posted By: Ed Davies</cite>Posted By: Jeff B: “I'm not sure how to interpret the results as it surely cannot mean for example that at 0C and a wind speed of 55 mph the heat requirement to maintain an indoor temperature of approx 20C would be nearly 5 times as much as that required when there is no wind at all at the same exterior temperature?�

55 mph (24.59 m/s) is pretty extreme. There have been gusts here this winter just over that (maximum 25.7 m/s on Nov 18th) but the highest sustained wind was 18.5 m/s (41.38 mph) for the same half hour.

Agreed, though, that the equation probably breaks down at the higher wind speeds though that's not obvious from the scatter plots in my earlier posts on the subject such as<a href="https://edavies.me.uk/2019/01/continuous/" rel="nofollow">https://edavies.me.uk/2019/01/continuous/</a>. Of course, a house with reasonable airtightness would be expected to have smaller numbers for those parameters.</blockquote>

I can see now that this is a fiendishly complicated business! There are cold days with or without wind or cold days with intermittent wind. A further complication in my case is that we have solar thermal so the difference between a cold sunny day and cold cloudy day can have a big impact on the DHW heating requirement which in turn affects the amount of pellets burned! (Note: our wood pellet boiler serves both C/H and DHW).

Attached is a plot of pellets consumed vs degree days for February (1st to the 18th). The r squared value (correlation coefficient) is pretty poor but there is a visual trend at least. I realise the degree day figure does not take the wind chill factor into account but I was just interested to see if this would work. Also degree day data are readily available for my postcode.

There are two major outliers (circled) and when I looked into these apparent anomalies I found that the lower one at 12.9kg/8.08 degree days was on the sunniest day of the month (9 kW PV against the average of 3.5 for the month), hence reduced heating demand for DHW. The higher one at 22.9kg/7.00 degree days was on the 14th Feb, the day after the coldest day of the month (13th Feb, with 25.5kg pellets used) and the house was still "cool" from the night before and therefore required more heat.

I haven't done the calculation but I suspect that leaving these two outliers out would improve the r squared value quite a bit!

Leaving out the two outliers, r squared = 0.64. (was 0.42).

Posted By: meThey both look the same distance from your trendline so shouldn't affect the R².

Sorry my typo - should have said they shouldn't affect the trendline, not the R².
I tinker with this kind of stuff to look busy and avoid decorating....

Posted By: owlmanAs you say Peter there are so many variables, so as to make any calculation a bit of a nightmare.
However, the nearest rough guide/ rule of thumb I got to on an internet calculator, was; in order to achieve approx 21-22 degrees C. 1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).

Our place is 180 sq.metres, so multiply by 2.4 (average room height) = 432 cu.metres. Divide by 14 = 31. So 31 kW required to keep house at 21C when outside temperature = 0C. We burn approx 22 kg of pellets on such days, equivalent to 100 kW, so either the formula is very dodgy or our house is appallingly insulated!

Posted By: owlman1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).

Hmm, so if our property was averagely insulated, we'd need about 30 kW. As it is we need 1 kW (about 3.5 kW for 7 hours). So clearly, estimating how average your insulation is, is quite important.

Posted By: djh

Posted By: Jeff BWe burn approx 22 kg of pellets on such days, equivalent to 100 kW

So many kg of pellets would be equivalent to so many kWh, a measure of energy. kW is a measure of power, so so many kg of pellets per day is indeed a power, but I'm not sure that's what you meant. 100 kW would make your place very toasty indeed, no matter how poorly insulated, I think.

The 100kWh output is spread over about 11 hours, which is the total time the boiler runs every day. Yes, if I set fire to the whole 22kg of pellets in my fireplace the place would indeed be pretty toasty (for a short time anyway!).

Posted By: owlmanAs you say Peter there are so many variables, so as to make any calculation a bit of a nightmare.
However, the nearest rough guide/ rule of thumb I got to on an internet calculator, was; in order to achieve approx 21-22 degrees C. 1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).

Does that mean 1 kW per hour for every 14 cu.metres? If so, then for my 432 cu.metre house I would need 432/14 = 31kW every hour? If so, then my average of 9kW per hour doesn't seem too bad!