Welcome to the forums @larry. We covered heat loss calculations in a recent podcast featuring our very own @jamespa 

In direct reply to your question, to ensure MCS compliance when assessing heat loss, it’s essential to follow the MCS guidance on heat loss calculations, which is typically based on room-by-room analysis using U-values for walls, windows and doors, along with ventilation losses.

Regarding blower door tests, yes (as far as I’m aware), the results can be factored into the air changes component of the calculation. Typically, the result is expressed in air changes per hour. For MCS purposes, you can use this value in place of standard assumptions for infiltration rates, potentially giving you a more accurate figure.

However, to apply this on a room-by-room basis, you’ll need to adjust the whole house result proportionally for each room, based on its volume and any specific factors that may affect air leakage in that space (external walls, windows, etc.).

Thanks @editor 

I watched that video yesterday - Excellent.

I've been looking into the blower ACH50 / 20 method according to the SAP guidance. I’ve also just read a study that indicates this divisor could actually be as high for 37 in the UK.

This all ties in with the fact that your associate in the video has never seen a blower test that indicated over 1 ACPH. 

I believe we're permitted to take further evidence into account within the MCS process, so surely a blower test should me mandatory, at least for pre-2000 builds.

Would it be considered reasonable to adjust the notional room by room ACPH on a volumetric basis, to give a whole house ACPH equivalent to the blower test?

How would we best integrate the point-considerarions such as open flues etc...?

Anyone's thoughts would be greatly appreciated.

Posted by: @larry

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surely a blower test should me (sic) mandatory

Any talk of 'mandatory' starts the hairs on the back of my neck rising. In close proximity to any mention of MCS, a discredited bunch of goons and stooges if ever there was, and my blood pressure starts to rise as well. 

The whole business of heat loss calculations is very far from satisfactory. Posts on this forum and no doubt elsewhere using measured estimates of heat loss suggest the standard calculations are very inaccurate. In my case, for example, the calculations estimate a heat loss of just over 12kW, while an estimate based on how much heat is actually consumed comes closer to 8kW. If that is correct, it may well not be, then the calculated figure is a 50% over-estimate of the real figure. Furthermore, the standard MCS method is pure whatiffery (what if the U values of my walls is X, the U value of my windows is Y etc), all done by the book, with the only actual measurements taken being dimensions. Adding in measured as opposed to guessed air changes per hour values might improve things a bit, but if the rest of the calculations are way out, then just having more accurate air change data still wont produce an accurate heat loss.

What we need is empirical evidence. I haven't done a proper literature search, perhaps it is time I made a start. Or perhaps someone already knows of relevant studies?   

Hi @cathoderay 

There's lots of good empirical studies out there. Solid wall real-world heat losses by Historic England is a good one. Ventilation rates, etc. 

My understanding is that we're free to vary the MCS spec, with good reason and by agreement with the client, but we then carry the can.

Does my method of adjusting ACPHnatural based on the ACH50 blower test seem reasonable to you?

I've got reasonable faith in modern u values, it's really just the older properties and ventilation rates that mess it all up.

Does anyone know how MVHR should be factored in too?

Posted by: @larry

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There's lots of good empirical studies out there. Solid wall real-world heat losses by Historic England is a good one. Ventilation rates, etc. 

Thanks, that's useful to know. I'll see what I can dig up.

Posted by: @larry

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My understanding is that we're free to vary the MCS spec, with good reason and by agreement with the client, but we then carry the can.

I guess that may mean you are an installer (which is fine - all are welcome here!)? But doesn't deviating from MCS block many grants? I'm pretty sure my installation had to be MCS compliant to get a grant (one from the 2021/2022 LAD scheme). 

Posted by: @larry

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Does my method of adjusting ACPHnatural based on the ACH50 blower test seem reasonable to you?

I've got reasonable faith in modern u values, it's really just the older properties and ventilation rates that mess it all up.

Yes it does, but it adds a new layer of complication and expense, to what is already a complicated and expensive process. If it can be shown to add value, then the case for using it becomes much stronger.

My property is a classic older property where you might expect the ventilation rates really would mess things up adversely, ie increase the heat loss,  but the odd/curious thing is the empirical heat loss I mentioned earlier (~8kW) is much less that the calculated loss (12kW). If the ~8kW is the real heat loss, then either the presumed U values or the air changes/hour (or both) used in the calculations are out of whack.   

This is the solid walls one....

https://historicengland.org.uk/images-books/publications/spab-rr1-uvalue-report/

Posted by: @cathoderay

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I guess that may mean you are an installer (which is fine - all are welcome here!)?

Studied Mech.Eng and used to fit heat pumps about 15 years ago. Now I do surveys and sales for an installation company. Always trying to learn more and refine the process, despite the obstacles in our way.

Posted by: @cathoderay

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If the ~8kW is the real heat loss, then either the presumed U values or the air changes/hour (or both) used in the calculations are out of whack.   

No doubt both will be out.

If MCS could give specific guidance on the application of blower tests then we could all get a lot closer.

Building fabrics do need better consideration than the typical surveyor will give them; but I'd say that with due diligence, we can get pretty close on most fabrics over the last century or two.

It's really the ventilation, internal adventitous gains, convection etc. That we need more practical guidance on.

Posted by: @larry

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Studied Mech.Eng and used to fit heat pumps about 15 years ago. Now I do surveys and sales for an installation company. Always trying to learn more and refine the process, despite the obstacles in our way.

Very good to have your experience and expertise here, I am sure you have much to offer which I am sure others will welcome. 

Thanks too for the U Value report link, I have just had a look and in the Intro it says "The key findings concern the differences between in situ test results and those less favourable to traditionally built walls obtained through theoretical calculation models." If I've read that right, I think it might be saying 'theoretical calculation models' over-estimate ([are] 'less favourable to') heat loss for 'traditionally built walls'. If so, interesting stuff! 

Posted by: @cathoderay

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If I've read that right, I think it might be saying 'theoretical calculation models' over-estimate ([are] 'less favourable to') heat loss for 'traditionally built walls'. If so, interesting stuff! 

Very much so.... some light for the long winter evenings ahead!

Posted by: @cathoderay

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If I've read that right, I think it might be saying 'theoretical calculation models' over-estimate ([are] 'less favourable to') heat loss for 'traditionally built walls'. If so, interesting stuff! 

Very much so.... some light for the long winter evenings ahead!