https://www.ubakus.de/en/r-value-calculator/

This tool lets you input the makeup of your wall, ceiling, roof, etc, and calculates U/R-values.

It can also simulate summer comfort, thermal mass, dew points, condensation in the insulation, whether it will dry in the summer or not, etc. Extremely useful.

Posted by: @bobflux

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This tool lets you input the makeup of your wall, ceiling, roof, etc, and calculates U/R-values.

Excellent find, thanks for posting the link here.

@bobflux Thanks, that gives me something to check the inbuilt u values with. There looks like a lot more once you've found your way around it.

@cathoderay https://www.stelrad.com/starsapp/login - you have to setup an account and I can't remember how onerous it is as it was 10 years ago when I started using it.

MCS and British standards do have air change values that generally seem to be 0.5 (I assume that's room volumes but not fully checked that yet) they also include for chimneys and extractors so comprehensive.

Just had my first quote of over £18k so if that's the general cost of an ASHP + central heating install for a small 2 bed cottage then my journey will be stopping and i'll go for LPG.

Posted by: @paul1098

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you have to setup an account and I can't remember how onerous it is as it was 10 years ago when I started using it.

I fully sympathise with any wish not to have to sign up to spurious accounts but the link I posted was for the correction factor table, which is freely available, you then do your own calculations.

Posted by: @paul1098

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MCS and British standards do have air change values that generally seem to be 0.5

ACH value recommendations have come down recently, but again best to use numbers that make sense to you. I've always taken the value to .mean what it says' 1 ACH means the volume of air in the room is replaced every hour.

Posted by: @paul1098

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Just had my first quote of over £18k so if that's the general cost of an ASHP + central heating install for a small 2 bed cottage then my journey will be stopping and i'll go for LPG.

Is that with or without the BUS grant? And how much extra work does it include?

Posted by: @cathoderay

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I fully sympathise with any wish not to have to sign up to spurious accounts but the link I posted was for the correction factor table, which is freely available, you then do your own calculations

Standard rad output is proportinal to dt^1.3 where DT is the difference between room temp and average rad temp.

No need to sign up you can calculate it yourself unless you are using funky rads.

Posted by: @paul1098

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Just had my first quote of over £18k so if that's the general cost of an ASHP + central heating install for a small 2 bed cottage

Unless there are some major difficulties this is high, very high.  It's standard practice throughout the construction industry to provide a very high quote if you don't want the work.

My recommendation is get more quotes and as @cathoderay invites tell us about the job so we can give you a steer.

Posted by: @jamespa

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Standard rad output is proportinal to dt^1.3 where DT is the difference between room temp and average rad temp.

No need to sign up you can calculate it yourself unless you are using funky rads.

The freely available table I linked to just simplifies the calculation to a single multiplication:

As you can see, the correction factor is about 0.5 at typical to higher (eg my system) heat pump delta t values, hence the half the delta 50 output rule of thumb. For lower delta t values, one third of the delta t output isn't a bad estimate. But for a full spec, you need to use the correct correction factor for your particular delta t. 

Posted by: @cathoderay

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ACH value recommendations have come down recently, but again best to use numbers that make sense to you. I've always taken the value to .mean what it says' 1 ACH means the volume of air in the room is replaced every hour.

I always thought the same but I have seen m3/m2 quoted which is got me wondering but that could just be a mis-quote.

Posted by: @cathoderay

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Is that with or without the BUS grant? And how much extra work does it include?

@rob-of-york My reasoning for the move away from storage heaters was to make life easy when the house is sold.
I think that if i can get A2W at a sensible price then it would be more acceptable to the general public than A2A although A2A is probably preferable to storage heaters.
LPG might not be ideal but it is what a lot of people are used to when 'off grid' and not able to fit oil storage.

The first quote was a toe in the water to confirm that it was possible to fit an A2W system. More quotes required and probably from good old fashioned plumbers that do full systems as well as A2W and also some companies doing A2A.

The self imposed constraint i have is value for money, if the new heating system can be close to cost neutral when compared to the increase in house value then it's worth doing if not i'll stick with my storage heaters.

Posted by: @paul1098

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I always thought the same but I have seen m3/m2 quoted which is got me wondering but that could just be a mis-quote.

I have just had a look at how the freedom Heat Loss uses and calculates ACH values. The actual values are by default look up values based on room type from a hidden table, which has by it "m^3/hr per m^2 of xternal area at 50pa". Go figure... The actual calculation to get the resultant loss in watts for bedroom 1 is =((B25-$B$13)*0.33*(B31*B26)*C39) which breaks down to (design room IAT - design OAT) x 0.33 x (room height x floor area) x the looked up ACH value (1.00 in this case). Most online sources say the ACH number represents the number of total air changes within one hour, ie a value of 1 means all the air is changed once an hour, 2 means twice an hour etc ie our general understanding is correct. How that simple concept then ends up with units of "m^3/hr per m^2 of xternal area at 50pa" is beyond me. To me, the unit is 'air changes per hour' and it simply means what it says! 1 ACH means the air changes once an hour! No doubt others (@jamespa? @rob-of-york?) can enlighten us further.

Posted by: @paul1098

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That included the BUS. It included for 5 rads, HWT, controller and central heating pipework.

Just to be absolutely sure, total cost is just over £18k, of which you would pay that less any grant you get?   

Posted by: @cathoderay

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1 ACH means the air changes once an hour! No doubt others (@jamespa? @rob-of-york?) can enlighten us further.

Exactly that.  Dimensional analysis (the powerful and occasionally useful technique of working out what the answer and the formula is measured in, in terms of the fundamental dimensions of the universe - length, time, mass etc) will confirm.  I will post the full explanation later if nobody else does and anyone is interested (both of which seem unlikely)