@chansug Welcome to the forum.

Could you specify what flow temperature and design OAT the three quotations are given for? 🙂

Also a description of your property might be useful too

@bontwoody thank you for a quick reply.  The heat geek trained surveyor was the only one who mentioned the OAT as -1.5 degrees. The other two reports do not specify this. The flow temperature is 50 degrees for all three quotes.

I live in a 4 bedroom house detached with an extended kitchen which needs an extra radiator. The loft insulation is good at 100mm and part cavity wall insulation.

@chansug An increase in that loft insulation would be a good investment too. You may be able to get a grant from your local authority to cover the cost. Regards, Toodles.

In no particular order some thoughts:-

Clivet is a badged Midea and personally I wouldn’t have one given me.

Since a Heatgeek trained installer says your microbore is acceptable that helps the confidence in the other quote.

Does the tentacled quote warrantee the SCOP? That is useful to know. It will make a difference to your operating costs and allows you to calculate the payback time on the price difference.

We found some bits of our walls needed cavity insulation which we promptly did since a back of envelope calculation said an 18month payback time. The same will apply to extra loft insulation.

If your boiler is really wonky the waiting time for an installation is crucial and a popular installer may have a wait time of months which is too long with a failed boiler. The big company may be quicker.

That range of heat loss estimates is good, some people have had factors of two. What is your annual gas bill? There are several rules of thumb/ sanity checks you can use to determine which is closest.

See

PROTONSFORBREAKFAST.WORDPRESS.COM "https://protonsforbreakfast.wordpress.com/2022/04/05/what-size-heat-pump-do-i-need-a-rule-of-thumb/"

What Size Heat Pump Do I Need? A Rule of Thumb | Protons for Breakfast

https://youtu.be/hCeghKa3liM Friends, a few weeks ago I wrote four articles about using the idea of Heating Degree Days to make simple calculations about heat losses from one's home. Article 1 was an introduction to the idea of Heating Degree Days as a general measure of the heating demand from a dwelling. Article 2 explained how and why…

Good luck!

@judith When we had our loft insulation improved, we approached the local authority who informed us that there were grants available as long as we used an installer on their approved list This we did; very few conditions had to be met other than that the present insulation was below recommended minimum (it was) and that we had to clear the loft of all clutter, this we were doing at the time anyway. The insulation is now in excess of 300 mm. all over. The job was done, I signed a form and the local authority dealt with the payment. We have a loft with a series of hazard signs hung in it to warn of the need to use breathing apparatus if working in the loftspace! Regards, Toodles

Thank you @toodles and @judith 

I will certainly ask the question related to warranty for scop. If the firm who have quoted for microbore changes are willing to change the heat pump to another brand like Vaillant, Grant etc (which they said that they would accommodate) is it a good idea to change to 15mm pipes? HG trained firm are not changing microbores but still cost similar. 

And I can't find any reviews for Clivet online. Is it because it is a rebadged midea which does appear to have mixed reviews.

Thank you for the guide. According to the calculations there, I need a 8kw heat pump. We use anywhere between 18 to 22kwh gas annually.

@chansug

Good advice above. 300mm is considered acceptable loft insulation these days 🙂 The fact that some of the quotes havent specified the flow temperature at a specified OAT is worrying to me, but since you have the heatgeek at -1.5C thats probably what it is.

Personally I would find the 50C flow a little too high and you will pay for it with your bills in the long run. If you are at all DIY competent the obvious choice for me would be Octopus and then upgrade radiators/pipework in your own time with the money you save. I also would avoid the third option for the same reason as above, so if you dont fancy DIY (although £5500 with buy you a lot of plumbing!) then number 1 would be my preference.

@chansug which room has the 15mm pipework, what size is it?

@bontwoody none of the rooms have 15mm pipework. It is microbore throughout.

@chansug Sorry I misread and mistyped! 10mm copper pipe can transmit about 1.15 kW of heat with a delta T of 5C so that would place a limit on each radiators output if it wasnt replaced. If you know the heat loss for each room you could check if that is enough. Have a look at this link:

HEATGEEK.COM "https://www.heatgeek.com/does-my-pipework-need-upgrading-for-a-heat-pump-with-cheat-sheet/"

Heat Pump Piping: Do You Really Need to Upgrade Your Pipes?

Get expert guidance on heat pump piping sizing! Our comprehensive guide covers everything you need to know about heat pump piping sizes.

@bontwoody But I thought all heat pumps are designed to 50c specification, am I wrong in assuming that? All quotes i received so far are designed to 50C specs so I thought that is standard.

Also, the HG install won't save me any money as it costs the same as the last quote who are upgrading the microbore to 15mm for the same cost. 

And, I will not attempt to upgrade my pipework, too out of reach for my minimalist DIY skills.