Posted by: @singlespeed

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If your calculation is actually based on a survey of the property, you should be able to gauge how accurate its going to be, by how much needed to be guesstimated due to hidden features.

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Not sure I agree entirely with that, @singlespeed.

From all we've seen on this forum, the heat loss survey of most houses appears to involve about the same amount of guesstimating since the number of unknowns usually turns out to be about the same. What varies far more is now close each of the estimates are to reality. For example, almost all surveys will have to estimate the air changes but some will get it close and some will get it wildly wrong. As a result, knowing the air changes are being estimated doesn't give us much of a clue about how accurate the survey will be.

To put it another way, one would expect a survey based on ten estimates to be far less reliable than one only relying on five, but if all of the ten are pretty good guesses and one of the five is way out then we're already in trouble. As has been highlighted in many other threads over the years, I would suggest the only way of gauging how accurate the survey is would be to cross check it with known good historical data like gas consumption figures and so on. 

I have just come back form a full design on a 140yr old building running on oil, the customer paid for my time and I spent 3hrs designing and running through multiple options to find the correct solution for them.

Each time we changed the design I explained the potential consequences, they can choose to change everything now, rads later, cylinder, no cylinder and so on, each change I show what the difference in design makes V cost.

In this case the ASHP saves some £2,000 in running costs due to oil being through the roof. It makes sense in this case we go for the win on the energy cost saving and perhaps change rads later room by room as the rooms get decorated over the next 3 years or so as thats the clients plan, client will keep the original cylinder as its modern and in good shape.

I think what we (as designers) should be doing is advising the best we can using our experience and the tools we have and then take responsibility for the final design. I think any customer should be a little concerned about any company regardless of the badges behind them, if that company or designer cannot reasonably answer most question on the day by either, answering in writing later, calling the office for tech support or answer all of your questions on site there and then. Being fair with some companies models, the person on site taking the measurements may not be the actual designer and in fact be more like the representative sent to get the relevant info for the designer. In this case they should just be able to get hold of the office to answer the customers questions or reply in writing very soon after.

There is no set of correct answers, all buildings can be unique in some way, there is only the relationship between you and your designer, I think in large this is what you are paying for when you are being charged for the heat-loss and design, you get the designer and their knowledge, their ability to apply that knowledge and the relationship with any trust you build, before, during and after the installation. Customers should be for 10 years + not an install and done, if you are not getting this kind of service then it is worth looking further. It is hard to filter though and find good designers / installers sometimes but they are out there and there are some really good companies.

@ashp-bobba It is very pleasing to me to hear that the potential customer is so engaged in this way for as you say, the relationship need not stop after commissioning day. I am still in contact with my own installers 3+ years since the installation and in fact, they are coming next week to do a survey for Air Con for us and again at the end of October to service our Daikin heat pump. Having found a competent company, the relationship is still building and I can rest assured. Regards, Toodles.

Posted by: @singlespeed

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I was only paraphrasing what Adam said in the video.  So your disagreeing with his stance. By his own metric the quote which started this topic was made by a salesman as there's no flow temp and the heating requirements/outputs don't add up.

I suspect 4 yrs ago, their approach had not got to this point. It was innovative as I think most installers were insisting a heatpump would need a buffer tank and new rads (and maybe pipework and UFH). 

They are now installing Vaillant, not sure if same 4 yrs ago. 

Even if heatpumps exist for decades, the recent models have improved.  

Posted by: @franszo

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Hi everyone! Hope Im not posting in the wrong post, but this seems to be the most relevant for my situation as well! And I could use some help

Just had a HG heat loss survey, and got the results.

- No flow temperature being mentioned anywhere. Better ask the installer who came out or message HG?
- Surveyed heat loss: 6.3 kW turned out to be better than the estimated time 6.88kW was. 
- They say I need to replace the hot water cyilinder
- House is a 1998, well insualted, (cavity+ 10mm loft insulation) 110m2
- I have a 6.7kW Pv array along with a (13.5kw) Tesla Powerwall 3 

now where I could use a little help is the options I've got. and see if pricing is correct (I'd like to stick to Vaillant)

Cheapest option would be
- 5kW aroTHERM PLUS along with a
- uniSTORE Pure 175l Slim cylinder.
- and 0-2 radiator change included
- 340- 370% guaranteed efficiencey
- £5,200 after BUS

Based on previous posts its not only me thinking the numbers doesn't add up....

next up:

- 7kW aroTHERM PRO along with a
- uniSTORE Pure 210l Slim cylinder. // not sure why no option to chose the 175l mode, which would be sufficient for me
- and 0-2 radiator change included
- 340- 375% guaranteed efficiencey // negligible difference? 
- £5,850 after BU?
// still this seems to be the best option>

or
- 7kW aroTHERM PLUS along with a
- uniSTORE Pure 210l Slim cylinder.
- and 0 radiator change included
- 340- 345% guaranteed efficiencey
- £5550, after BUS

and Im not too happy with the placement either. the best spot would require 15-20m extra piping all the way up on the wall into the loft, and then to the cyilinder. which cost extra £3,000 is that realistic? 

Also just checked these ASHPs are around £4-4500 the cyilinder £1500 (definitely cheaper for the installer), is the installation, electrics and pipework, replacing 2 rads really £6000 for 4 days of work?
Octopus just installed their 9kW cosy in my close relative's home, same work, new cylinder, and a lot of extra outside pipework, insulated, no rads replaced, was £3200 after BUS. seems like a huge difference for me

I would appreciate any help, thank you kindly!

After my installer didn't reply for more than a week, I've got a reply from Heat Geek, stating `the flow temparature currently ranges from 51 to 58C, depending on the combination I choose`

Im quite torn on the flow temperatures, also which unit to choose. My installer also confirmed that extra 15m pipework to place the ASHP unit where it would be the most ideal, cost £3000, that covers: extended pipework, insulation, cabling, access requirements. (no scaffolding).

I reckon this would mean, £8500 for a 5kW Vaillant AroTherm, and 58C flow temp 😀 for 8,5K doesn't sound ideal to me. 
I'll rather wait to see what Octopus says for the same. My current plan is to use gas for the upcoming winter, and see what offers are on during next summer. AFAIK Octopus had 15% off between June - Aug.

Posted by: @franszo

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I'll rather wait to see what Octopus says for the same. My current plan is to use gas for the upcoming winter, and see what offers are on during next summer. AFAIK Octopus had 15% off between June - Aug.

Good plan.  If you can get half hourly meter readings and, if your house temperature isnt moderately constant log indoor temperature if you have a suitable device.  Then you can determine heat loss pretty accurately. 

Turn down the flow temp to say 50C and see how it works operating 24x7 or thereabouts.  Most likely this will reduce your gas consumption and improve your comfort.  

Its what I did and certainly did not regret it.