Deleted 6 December 2022 at 12:09PM edited 12 January at 11:56PM in Green & ethical MoneySaving 35 replies 1.2K views

zeupater

Hi

Just an update ... 

The timing of this discussion has been quite fortunate .... having mentioned the number of points we can measure temperatures yesterday I gave them cursory check today and found that one area which seems to be cooler (compared to normal differentials) than it should be .... seems that some laurels have grown taller than I thought & must have been casting afternoon shadows across a large window for the past few weeks whilst the sun's arc is low ....

.... not going out to sort it now as it's still a little chilly, it may even have to wait for the normal spring garden tidy-up, but we'll see how it goes ... weather-station was registering -5C here at 7am ... thank goodness for remote monitoring as I wouldn't be going outside just to check ...

Sunny, 19.9C 20.8C with 38% humidity where I'm sitting, so a little dry, but at least that means nothing should be getting damp elsewhere ... still no logs or gas, just the small heat-pump running on solar - may be different tomorrow as the solar thermal suffers with lack of photons and hours at this time of year and MrsZ's shower temperature threshold is perilously close ...  

Z 

QrizB

Deleted_User said:

QrizB said:

Deleted_User said:

So really - our insulation isn't bad in the least. It's a warm house - it was also a warm house when we used gas CH. I just want to get an idea of what's possible with latest technologies.
...
As I've said, I know what I have.

Is your house of traditional construction, or something more modern?

We've got a 1950s semi with brick cavity external walls and single brick internal walls. all those bricks give us a lot of thermal mass.

Back-of-an-envelope and subject to revision, I think our walls contain around 50 tonnes of bricks which gives a heat capacity of roughly 11kWh / deg. C. So for each degree C that pur house cools, we'll be losing 11kWh of heat.

If your house is eg. wood-framed, or made with lightweight block, you'll have a lot less thermal mass. With equivalent insulation it will cool more quickly.

It's a timber framed, 20 year old house. It's always been a warm house.

I have no concerns about the insulation in my house. It's warm and cheap to heat (whether by gas  CH as in the past, or by woodburner now).

That's great for you, and now we all understand why your 20-year-old timber-framed house cools down so much more overnight than my 1950s brick-built semi does. Despite its insulation, it has less thermal mass.

I suspect many of the people you're comparing yourself to in the opening post:

Deleted_User said:

I'm reading lots of comments on these boards relating to how well / long a home should hold onto heat, and how low an unheated home should go. Some of it sounds a bit suspect to me (even the best insulted house will eventually be the same temp as outside if there's no heat source).
...

This week the lounge is 15 - 16 degrees in the morning and continuing to drop fast. The rest of the house is ranging from 10 - 13 degrees. The (posh, rarely used)) lounge that was 10 degrees when I got up has now dropped to 8! (It's still not above freezing outside). As  the day goes on I'll open more and more internal doors and by tea time the whole house will be warm.
As I say, it's all dry and comfortable. Our 3kw logburner is very economical with wood and coping well - we get most of our wood for free. But do we spend our money stocking up on extra fire wood so we can toss it in the fire with gay abandon for future years -  or do we invest in more insulation?
I would love to know how a similar sized bungalow that's new built with state of the art insulation would do.

... also have homes of traditional construction which cool down less overnight as a result.

zeupater

Deleted_User said:

[...]
One person insisted that in a well insulated house with no heat source, temperatures should never drop to 12 degrees - even when it's very cold outside!  So better than a high spec thermos flask?

As I say, it all sounded highly suspect to me. Which is why I was keen to get real world examples of what people are achieving in houses with state of the art insulation. So not theory or advice - just their hard numbers. 

I know the theory, but to people that actually have state of the art insulation - how much did it cost them to retrofit it, and how well does it really work (i.e. how quickly does the house cool when heat sources are switched off). ?

Hi

Well, sitting here in a property which you would classify as being better than a "high spec thermos flask", maybe I could propose a significant reason ..... THERMAL MASS .....

A flask containing 1 litre of liquid would have a mass of it's structure plus 1kg, with the centre of that mass being only a few inches from the ambient temperature .... generally, heat being lost from where it's needed will be as a result of it rising as a result of thermal expansion until it's vertically confined by either a solid obstruction or thermal stratification ...  or ... creates a thermal gradient from the centre of the mass to the outside ..... don't worry about radiant or convected heat as that really describes the dispersion of heat/energy only after it's reached the outside of the 'container' , it's heatloss through conduction we'd be concerned about for the moment.

Okay, so we have a small container containing a litre of boiling water sitting on a table in an ambient 0C ... we have 100Wh.t of stored energy differential, but importantly, because of the distance from it's core (100C) to the outside (0C) is so small the thermal gradient is steep ... ie there's very little resistance to the transfer of heat through the materials, and little energy available to be transferred in the first place  .... because temperature differential in a house at 20C would be far lower and the internal dimensions would be far greater, the resistance to thermal conduction will be far greater and the thermal gradient will, on average, be extremely shallow .... also, the stored energy will be far greater, not 100Wh with a steep gradient, but many thousands, or even tens of thousands times more heat stored in mass which is reluctant to give it up, and that's before the planet below the insulated space starts replenishing lost heat ... this is what someone was probably trying to explain about dropping below 12C, which is at the top end of the the average UK ground temperature range at 1m depth and will certainly act as additional thermal mass, but it's probably ambitious to claim it's a temperature floorpoint if there were no passive heat-source (solar gain etc) ...    

So, what happens if we improve the already high resistance to conductive flow further  to prevent the heat escaping, ie through insulation? ...well, that's where the science behind what we've been describing comes in and guesswork should leave the building (pun intended!)        The resistance to heat transfer of materials is generally referenced as the r-value which related to heat transfer over distance ... you may see insulation material specifications mentioning their r-value, however, a more useful denomination is related to the thermal transmittance per unit of area for a given temperature difference ... this is normally referenced as the u-value and measured as the transmittance in watts per square metre of area covered for 1 degree C (/K) difference between the two sides of the material .... with this you can quickly calculate the likely heat loss through any material & then recalculate what it would be with different/additional materials  ... for example a poorly insulated loft with a current u-value of 3 will lose 3W/square metre for each degree differential between in house and the uninsulated space, so for a 100sqm loft with the house at 22C and the loft at 2C the heatloss is 6000W (3x20x100), that's 6kW in 1hour, so 144kWh per day.

Fine, following so far .... lets add insulation to the <2002 standard of u=0.25 and we get 12kWh (0.25x20x100x24) on the same basis .... improve that to a really good  u-value of 0.08 and it drops by a further ~2/3 to about 4kWh per day .... whilst averaging ZERO C outside! ...

Okay, so how do you justify the expenditure on the insulation? ... well, simply take the average daily temperature for the heating season for the area you live in and apply that to the difference between whatever the current insulation levels and whatever you propose to increase it to and calculate the energy saving potential at the temperature you heat your house to ... apply your specific heating source energy cost/kWh and you have valued your annual saving ... get prices for the improvement materials (or job) and then divide this by the annual saving .... you now have a current price ROI ...

... that's all you need to do - if the investment return period doesn't make sense, don't do it, if it does make sense, why delay as not doing anything is probably costing you money? 

This doesn't only apply to loft insulation, it applies to all aspects of the home, the walls, windows, doors and everything else will have thermal transmission data which can be applied ... that's how overall heatloss is calculated, so you could model the whole house yourself and use that to justify any changes that you can think of ....

Countering the obvious ... Yes, but ... in the example you're still needing 4kWh/day of heating just to cover heatloss through the roof ... yes, true, but if the low angle winter sun's shining through the windows today, 4kWh doesn't represent too many hours of solar gain if there's enough glazed area! .... 

 .... After all The cheapest form of energy is the energy you don't use!

HTH - Z

jacko220

Deleted_User said:

I'm reading lots of comments on these boards relating to how well / long a home should hold onto heat, and how low an unheated home should go. Some of it sounds a bit suspect to me (even the best insulted house will eventually be the same temp as outside if there's no heat source).

But anyway, I'm trying to figure out for myself what's worth improving and what isn't. My insulation is decent - there's no problems as such. It's a question of whether my money is best spent on increasing my wood stores or adding some insulation to result in LESS wood usage for years to come.

Variables that I can think of include:

• Detached, semi, terraced, flat
• Size of house
• Part of the country (how cold does it get outside?)
• Number of exposed, N/E facing walls
• Construction
• Current levels of insulation

We're in Scotland with a 20 year old timber framed 4 bed bungalow with very exposed N/E facing walls full of windows and bi-folding/french doors at the back. The house is pretty warm - well built. The extension is colder so it's likely we can do more there. But where will we get the best bang for buck (loft insulation? insulating wall paper? thermal blinds?)

Currently night time temps are -3 and we're getting maybe 4 degrees during the day. The house is being kept nice and warm by a logburner (running flat out all day).

Last week when it was a few degrees warmer we weren't needing to light the fire until lunch time. The main lounge (where we live) would still be 18 degrees when we got up in the morning and most of the house would be around 14 - 16 degrees.

This week the lounge is 15 - 16 degrees in the morning and continuing to drop fast. The rest of the house is ranging from 10 - 13 degrees. The (posh, rarely used)) lounge that was 10 degrees when I got up has now dropped to 8! (It's still not above freezing outside). As  the day goes on I'll open more and more internal doors and by tea time the whole house will be warm.

As I say, it's all dry and comfortable. Our 3kw logburner is very economical with wood and coping well - we get most of our wood for free. But do we spend our money stocking up on extra fire wood so we can toss it in the fire with gay abandon for future years -  or do we invest in more insulation?

I would love to know how a similar sized bungalow that's new built with state of the art insulation would do. 

You have "lightweight" wall, the timber frame and Rockwool, they are good at insulation providing you maintain the heat, however when you turn the heating off it will lose heat rapidly, You require thermal mass in the middle of the bungalow, which you probably have with the chimney to the log burner. Does the floor feel cold, I suspect it is insulated for the date you give but I am not knowledgably about Scottish Bldg Regs. If you have any question I would only be to pleased to answer them. 

zeupater

Deleted_User said:

. If you have any question I would only be to pleased to answer them. 

Here's one....

We purchased  thermal lining paper from someone that bought it but couldn't be bothered hanging it - so we got it very cheap (£10 a roll with free glue).

Where would you hang it?

1. On the walls of the main living areas where we have the most heat (even though they are already well insulated)?
   
   or
   
   
2. On the North and East facing walls of the house - mostly rooms we don't use as much in the winter (so don't heat as much)  but definitely cooler walls?
   
   

https://www.screwfix.com/p/wallrock-white-thermal-liner-wallpaper-750mm-x-10m/98119?kpid=98119&amp;ds_rl=1243321&amp;ds_rl=1241687&amp;ds_rl=1245250&amp;utm_source=bing&amp;utm_medium=cpc&amp;utm_campaign=MPX_UK_SHP_MAN_S_ALL_Decorating&amp;utm_term=4584138879768134&amp;utm_content=S - All Decorating&amp;ds_rl=1245250&amp;gclsrc=ds&amp;gclsrc=ds

Hi

Unless you are experiencing condensation/damp on the cooler walls where you're not heating as much you should be looking at the external walls in areas where the int/ext deltaT is the greatest as this will allow unabsorbed energy to find it's way to other areas when your internal doors are left open ..

.... however, although there's plenty of claims & anecdotal information regarding this type of product, there doesn't seem to be much in the way of published specifications of what that performance may be whenever I've looked  .... having 'said' that we have a similar product in one room and it does make the wall feel warmer when touched ... and yes, that is subjective/anecdotal too!

HTH - Z