How many kWh less heat needed with better loft insulation?

barker77

Is there a way to work out kWh heat loss easily for effectively almost no loft insulation to 200+mm ? Octopus have quoted me for 50c flow temps and I want to see if loft insulation would mean I could drop to say 40c 

Green_hopeful

Loft insulation is very cheap and not tricky to do. I can’t imagine living without it. I have topped up the insulation in every house I have lived in. I even topped up the insulation in my sons buy to let to keep his tenants as warm as possible. I don’t think it’s possible to say exactly what difference it would make. The Energy Saving Trust has some info. https://energysavingtrust.org.uk/advice/roof-and-loft-insulation/

barker77

Yeah I get that . Im trying to work out the difference and if it would get me down to 40c 

michaels

I think there is a website which suggests different potential energy efficiency improvements and their likely payback time. From that you could probably back calculate the expected energy use reduction. Although ashp may be more non linear over flow temp than gas heating.

NedS

barker77 said:

Yeah I get that . Im trying to work out the difference and if it would get me down to 40c 

You will need to calculate the heat loss of the property with and without insulation, and then model the heat output of the supplied radiators at the different flow temperatures to see if they meet the heat loss. Tools such as heatpunk may allow you to model the property with and without loft insulation.

Alnat1

Octopus do all their quotes at 50C and won't budge on this. Our system was installed in January and set up at this temperature but I soon tweaked the weather curve and found 40C was as high as we needed. 

It's recommended that everyone should have 300mm+ of loft insulation and this would make your house warmer however it's heated.  It's not difficult to fit and you'll quickly recover the cost with lower energy bills.

CuparLad

It is possible to perform heat loss calculations for any building. I'm in the process of having my house renovated and brought up to current Scottish building regulations. My architect has specified 350mm thick stone wool horizontal insulation over a plasterboard ceiling to achieve a u value of 0.12W/m2K (watts per metre squared kelvin). 

There is a useful guide to heat loss here - https://www.heatgeek.com/heat-losses/ which has a worked example about three quarters of the way down.

Remember heat loss is a function not just of the roof, but also the walls and the floors.

matelodave

If you want do do your own heat loss calculations try this - https://heatpunk.co.uk/floorplan you can then try different heat loss scenarios based on different insulation factors

However as @NedS suggests, flow temp is not necessarily the whole story - you need to factor in the size and dissipation of the radiators at lower temperatures, reducing the water temp does significantly reduce the heat output as does the way you use the system.

Have a look here at the Stelrad correction tables - if your rads have been sized for a 50degree flow rate (which implies a DeltaT of around 30 dgrees) then reducing the flow temp to 40 reduces your DeltaT to 20 degrees
https://www.stelrad.com/trade/stelrad-correction-factor/

Note DeltaT is difference between the rad temp and the room temp and radiators are usually rated at a Delta T of 50degrees which implies a flow temp of at least 70 degrees(70-20 = 50)