Heat Loss and Insulation



Heat Loss

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Introduction

If you have thermostatically controlled heating in your home, and most of us do, then your boiler will be controlled by the temperature measured in a heat lossparticular area in your home i.e. where the thermostat is placed! Regardless of how well insulated you home is the boiler will burn fuel and supply heat to your radiators until the temperature set on this thermostat is reached, before switching itself off. This does not mean that all of the rooms in the house are at the main thermostat temperature, their temperature will be dependent on the heat loss from the room, the radiator heat output of each room and the individual radiator thermostat (if you have them fitted). So the more you can do the reduce heat loss from your home the more rapidly the desired temperature will be reached and the earlier the boiler will switch off, ultimately reducing the amount of fuel you burn and amount you pay.

 

Solid Wall Insulation

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ROI
14.1-Years

If you have a very old house with solid walls then you are losing a lot of heat through the walls. Solid walls transmit heat at, at least twice the rate that uninsulated cavity walls do. Throughout the heating and insulation section of this site an average house is used and assumes that the walls have cavities, such that a three bed house with no insulation measures, is approximated to use 20,000kWh per year and the 5 bed house is approximated to use 30,000kWh. With a solid wall house the starting point is higher about 20% higher. So for this section we will use the numbers 24,000kWh for the smaller house and 36,000kWh for the larger house for the calculations.

There are two types of insulation for solid walls, external and internal. They are both expensive and both have their pros and cons, the energy savings trust has a good list of these on their site, they seem only to consider the savings if you are gas heated however (we assume). The main problem with internal insulation is the disruption to the house and the fact that your rooms will end up being a bit smaller, if however you are planning to redecorate it may be an idea. With the external wall insulation the whole house is likely to alter in appearance, this may be an advantage to some!

 

Cavity Wall Insulation

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ROI
2.1-Years

If you have cavities in your walls which are not already filled with insulation then you have a great opportunity to save quite a lot of money. Most household heat is lost through the walls and anything to slow this down helps. The story is similar to loft insulation, you can reduce your energy bill for heating by up to 25%, but again more realistically 20%. The table below calculates the effect of only insulating your cavities considering several main household fuels and estimates a payback time for the investment. For a larger house cavity wall insulation will cost £ 500 and for the smaller house about £ 350.

 

Loft Insulation

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loft insulation
ROI
1.8-Years

Since heat rises it follows that heat loss through the roof is a large contributor to energy waste in your house.  By installing modern 290mm thick insulation in your loft space you could save up to 25% of your heating bill but perhaps more realistically by 20% .  By upgrading old thin insulation you may also be able to save an additional 7 or 8% of you bill.  The cost of installing the new thick insulation or of an upgrade is fairly modest at about £ 300 for a smaller house and about £ 450 for a larger house.

The savings you could make by only installing loft insulation are given in the table below with various fuel types and their currents costs. The payback time for various installation costs is given in the second table. The reductions in CO2 emissions from your property will also substantially reduce.

This table shows savings with installing modern approximately 290mm thick insulation and the reduction of carbon dioxide emissions for 4 different energy demands, Check your bills to see what you use.
Financial savings by installing loft insulation - per year
CO2 emission reduction - kg per year
Below average energy use for heating per year
smaller house or warmer area
Average energy use for heating per year
the average in the UK
Above average energy use for heating per year
larger house or colder area
Source of energy for heating Savings with
original energy use
10000 kWh
Savings with
original energy use
15000 kWh
Savings with
original energy use
20000 kWh
Savings with
original energy use
25000 kWh
⚡ Electricity £0.154 per kWh
£308 (734kg) £462 (1101kg) £616 (1468kg) £770 (1835kg)
⚡ Gas £0.048 per kWh
£96 (420kg) £144 (630kg) £192 (840kg) £240 (1050kg)
⚡ Off Peak Electricity £0.075 per kWh
£150 (734kg) £225 (1101kg) £300 (1468kg) £375 (1835kg)
⚡ LPG £0.058 per kWh
£116 (460kg) £174 (690kg) £232 (920kg) £290 (1150kg)
⚡ Heating Oil £0.043 per kWh
£86 (520kg) £129 (780kg) £172 (1040kg) £215 (1300kg)
This table shows the payback time for installing loft insulation based on the costs of the fuels used and various cost options for installing the insulation.
Source of energy for heating Insulation install costs
select yours.
Payback time with
original energy use
10000 kWh
(years)
Payback time with
original energy use
15000 kWh
(years)
Payback time with
original energy use
20000 kWh
(years)
⚡ Electric £0.154 per kWh
£0
£150
£300
£450
£600
0
0.5
1
1.5
1.9
0
0.3
0.6
1
1.3
0
0.2
0.5
0.7
1
⚡ Gas £0.048 per kWh
£0
£150
£300
£450
£600
0
1.6
3.1
4.7
6.3
0
1
2.1
3.1
4.2
0
0.8
1.6
2.3
3.1
⚡ Economy Electric £0.075 per kWh
£0
£150
£300
£450
£600
0
1
2
3
4
0
0.7
1.3
2
2.7
0
0.5
1
1.5
2
⚡ LPG £0.058 per kWh
£0
£150
£300
£450
£600
0
1.3
2.6
3.9
5.2
0
0.9
1.7
2.6
3.4
0
0.6
1.3
1.9
2.6
⚡ Heating Oil £0.043 per kWh
£0
£150
£300
£450
£600
0
1.7
3.5
5.2
7
0
1.2
2.3
3.5
4.7
0
0.9
1.7
2.6
3.5

Is it worth doing?

This is one of the single most cost effective things you can do to save money and the environment, with substantianl reductions in carbon dioxide emissions. The payback time is very short and the long term reward is great. There are some grants from energy companies and local authorities (check with your local energy advice centre). If you cannot get a grant, supermarkets are also offering good deals and DIY installation will also save a packet! It is almost insane not to insulate your loft and even "top-up" insulation offer a better payback than any renewable energy option.

 

Underfloor Insulation

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ROI
3.9-Years
If you have timber floors, mineral wool insulation* can be used between the joists to insulate your floor.  Assuming this is the only insulation measure installed in your house you can reduce the amount of heat loss through your floor by about a half and can therefore reduce your energy bill by about 7 or 8%.

 

Lagging

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ROI
1-Year
It is fairly obvious that hot water pipes and hot water storage cylinders should be insulated to prevent heat loss.   Newer cylinders already have insulation pre fitted, but if your tank is older and un-insulated then according to the Energy Savings Trust  by fitting a hot water jacket you will save about £ 40 per year.  Your savings would be even more however if you regularly use an electrical immersion heater, since it costs a lot more to heat water with electricity.

Given that a new thick jacket (75mm) for a hot water tank costs about £ 12, it should pay for itself in less than six months.   Even upgrading an old thinner jacket, is worth considering and will pay back the investment in about 2 years.

This energy/money saving measure is almost a must do.  Even if you are renting off a landlord who is too tight fisted to put a jacket on the cylinder, you could buy one and take it with you when you leave!

Insulating hot water pipes will save you less, possibly £ 10 per year but DIY installation is very easy and materials will only cost about £ 10.  So it will only take a year to payback this investment.

Have a look at this on the forum regarding insulating pipes.
 

Double Glazing

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ROI
52.1-Years
Replacing your windows with double glazing to just save money does not actually make a lot of sense, you will reduce heat flow through you windows by at least a half and again assuming this is the only insulation measure installed in your house you should reduce you overall energy bill by between 5% and 10%.  For the smaller 3 bed house assuming you save the maximum 10% of your heating costs you should save  £ 60 each year if you are gas heated and if it cost about £ 5000 to install the windows the investment will payback in about 80 years.