@abernyte Google sheets is also another good option

Thank you both.  I got it to repair and open in Excel but it has excluded some data to do so. Will try Sheets

This is V3.3 on Google Sheets - https://docs.google.com/spreadsheets/d/1fI91GF163YuRITqNjPzBjlBfk1RT63ep8SxjkiIcp34/edit?usp=sharing

Apologies if the wrong thread for the query but has anyone used the likes of Veritherm or other companies that undertake measured heat loss calculations? 

I've asked them for a quote to complete, depending on the cost I might find it a useful peace of mind assessment given the house I'm in has bits that have been renovated/tagged on at different times. (but suspect this might bump it up from the "starting at £X ..." headline price)

While you would hope all of it was done to the building regs of the time (and therefore the U values in the spreadsheets would be of some meaning), and that the likes of cavity wall insulation was done properly, I'm still a bit wary.

When I'm looking at a 200 m2 footprint a bit of quick googling easily spits out anywhere between 8 to 16 kWh, lots of room for under or oversizing there!

Equally any thoughts on ACH values? Our Bathroom extractors seem a bit rubbish so those windows get opened to get some ventilation even in the winter, but otherwise no noticeable drafts etc 

I don't think there is a short cut to doing the full heat loss calculation to find a reasonably accurate figure, especially if your house as a variety of parts of different construction.

Using a very broad rule of thumb, a 1990's timber framed, single story house, reasonably well built should have an average heat loss somewhere around 53W/m2 which should give you 200m2 x 53W = 10.6kW so an 8kW heat pump might be a tad ambitious. If you allow a 6% oversize for hot water then an 11kW device is getting closer. There are so many variables we don't know on your build that this is a very speculative number!

@abernyte I was only thinking from the possibility of being belt and braces (although possibly quite an expensive set of braces!). Glad to hear that it sounds like there is faith in a (good/detailed) room by room assessment. 

I'll admit 8 was included perhaps as an exaggeration of the potential breadth of options. Ideally a properly variable (i.e. both compressor and pump) unit in the 10-12 kWh region would be easily rationalised by my gut. I am worried that some 12 kWh (and most larger units I've seen) would fall out of PD. Certainly would like to avoid planning permission if possible as that would guarantee another year on our current system. (Will likely make another thread on my planning queries if I can't find an existing one)

I've had one desktop quote that suggested the 11.2 kWh Ecodan, and Octopus seem to have come to a heat loss of 10kW (for the main house only) - suggesting the 10.6 kWh Daikin Altherma. Will crack on with attempting my own in the meantime whilst I wait for some local installers to get back to me. I'll post any questions I have here...

Out of curiosity is it standard to oversize slightly for DHW purposes?

Posted by: @declan90

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Out of curiosity is it standard to oversize slightly for DHW purposes?

The MCS V2.1 heat loss calculator will produce a reasonable figure for your house heat loss  but as part of the sheet asks for any DHW tank and size, if added, it will add in the appropriate "uprating" which for a 300ltr tank is 6% to ensure the fitted heat pump has sufficient grunt.  The most recent sheet seems to have it integrated into its calculation.

If you wish to lose several hours productively then search out the MCS calculator and just work methodically through filling it all in and see what it spits out.

@abernyte Thanks, I've drawn out my house schematic (and associated rad list) and started a few initial measurements. I was going to start with the Freedom spreadsheet (as it felt a little more accessible) and then build to the full MCS one. Hopefully getting a full set of detailed measurements will allow me to get through both. 

Any potential downsides (other than wasted energy/cost, esp regarding legionella cycles - which would be more relevant if under cycled) to oversizing the DHW cylinder? I'll be intending to size to what I think we might need in the future, but still a growing family at the moment so short-medium term our usage is likely to be a lot lower

I would be inclined to fit now what you will require later even if it is slightly large for your purposes at present. I suspect that the costs associated in changing the DHW tank later will outweigh the extra cost of heating a larger tank for now.

The legionella issue has always slightly puzzled me. Legionella is a relatively rare condition and most systems default to a DHW temperature of 50C with regular boosts to 60C. If your system uses an external plate heat exchanger then your hot water is even less exposed to the legionella risk and assuming you have good turn over in the pipe system then that small risk is even further reduced so I question whether the >60C  thermal disinfection cycle is really required.  Legionella doesn't survive below 20C and above 50C and I wonder if our costly legionella cycle is just an abundance of caution.

Personally, I have switched it off as the cold water main is always sub 20C and with hybrid solar thermal/PV panels there is a regular >55C disinfection of the hot water store anyway.

I think the lack of available HSE guidance other than that aimed primarily at commercial installations with a high likelihood of large, low turnover, hot water storage and potentially infrequently used outlets has led to a lot of the caution associated with legionnaires disease. (That and a headline figure of 1 in 10 contracting the disease die of related complications) 

Heat Geek had an interesting article on the subject and certainly sounds like, with good turnover in the hot water store, and low mains temp, that it's reasonable enough to decrease DHW temps and forgo 60C cycles. 

Hence I'd be wary if I didn't think I was getting the daily usage. 

It's laughable that one 'concern' listed for heat pumps is increasing presence of the bacteria on showerheads (due to lower store temps). It's like those people don't realise the shower head is well after the mixing valve so storage temp has little play on the head itself. I like a hot shower but 60C would be excessive for even me! 

To report back on progress, I've had a good go with the V3.3. Freedom spreadsheet but get overall losses in the 11.5 kW to 14kW (70 - 90 W/m3) region depending on what construction materials I select. 

My main conundrums / decision points have been:

1) Do I have faith the 2002 granny annexe was build properly to the prevailing building regs (I have no reason to believe otherwise but is missing a building control completion cert)

2) The works for the rear and side extensions commenced mid October 2010, is it reasonable to believe these therefore have to be to the 2010 building regs (that became active 01/10/10)?

3) Best way to represent cavity wall insulation for the original 1960s walls. Measuring a cross section of the old external wall downstairs it is 33cm (plastered on both sides). Is it reasonable to believe it might have had a 200 mm cavity (and therefore selecting "2000-2010 cavity with 200mm insulation")?

4) I plan on ensuring I have 300 mm loft insulation (rockwool), is selecting "celotex 300mm" reasonable?

5) I've used the room type ACH values rather than assuming any improvement to 2010-16 levels

As you can imagine with this many questions on the simpler version the full MCS one looks pretty daunting with myriad U values!

Any thoughts or feedback much appreciated 

Regardless of which calculator you use you are forced to make a number of educated guesses on the construction. I tend to err to the low side normally and if you know how much energy you currently use with the existing system, per annum, that should provide some sort of sanity check on what the spreadsheets spit out so if you multiply your annual heat loss by 1,500 for heating and 500 for hot water that would give an approximation of your kWh demand.