I started this off in the 'introduce yourself' thread, but wanted to give updates and didn't want to hijack the conversation there, so have created a new thread....

I live in a converted barn in Monmouthshire (South Wales). It was converted around 10 years ago and we bought it 7 years ago. It currently has an oil boiler which has been working well. However, last month, our oil delivery driver spotted a tiny crack in the top of the tank and refused to fill it up. We immediately entered 'panic mode' at the fear of running out of hot water (not using heating at the moment but that will be needed in the next month or so...) as we only have about a quarter of a tank left.

I initially reached out to a couple of local heating companies to enquire about replacing the oil tank. It turns out that our current tank is located in a position that would not comply with current build regs (and probably never did) and so replacing it involves more than a simple swap-over: we'd have to either relocate it or build a fire-proof barrier around the tank to meet regs. Most companies didn't want to touch it with a bargepole, although one firm quoted £3,500 to replace the tank and make it regs-compliant.

Over the last few years, we've gradually installed air to air heat pumps in most of our rooms because in the summer the house gets very, very hot. It's south/south west facing and we have lots of floor to ceiling glass, so it basically acts like a greenhouse. We've been really pleased with the low running costs, which made me think about exploring using an electric system to replace the oil boiler.

Much googling later and I made a few enquiries to local MSC accredited ASHP installers. Our house should be well suited to ASHP because we have underfloor heating throughout - no radiators - and I was also optimistically hoping the costs would be favourable with the RHI scheme.

5 weeks in, I have:

* received one quote of £9.5k for install of 7kw Valiant Aerotherm Plus, 200ltr Valiant tank and Valiant controller. Estimated RHI payment of £9.1k. The quote was based on floor plans, an EPC from 2013 and the building survey we commissioned before buying the house. They've emphasised it's an estimate and will be confirmed after paying £500 for them to do the heat calc survey and new EPC. Originally I thought these guys were good, but I've emailed and phoned a couple of times over the last few weeks with questions and they've stopped getting back to me. Maybe they're just too busy.

* received one quote of £18.9k for install of 2 x 10kw Valiant Aerotherm Plus, 200ltr tank and controller. For this one, the company sent someone out to do a free heat loss calculation - they were here for about 2 hours measuring all the rooms up, so I'd imagine the 2 x 10kw spec is right but am hoping it is way over-egged. They've not included any information on estimated RHI payments.

* had a visit from a company to do a quick initial assessment and chat, he estimated 12 - 14k but wouldn't be able to give a final quote unless I paid £299 for a heat loss calculation.

* had a visit from another company to do a quick initial assessment and chat, he estimated 14 - 16k but wouldn't be able to give a final quote unless I paid £250 for a heat loss calculation. I actually felt the most positive about this company, all my communications with them have been really good, they are clearly knowledgeable and appear to have a good reputation. They also promise a 10 year parts and labour warranty, which is way more than the others. They have only been in business 4 years though so how worthwhile this will be remains to be seen. That said, I agreed to pay the £250 for the heat loss calculations, this happened last week, so I am expecting to hear the results of that and get a final quote in the next week or two.

I've found it really hard to assess and compare suppliers, particularly because they are unable to quote without first paying for the heat loss survey. Annoyingly, none of the companies were willing to accept heat loss survey results from another company, which would effectively mean paying for the same survey several times just to get comparative quotes.

One potential pitfall to my switch to an ASHP is needing a water tank. Our current system is a combi oil boiler and we have no standalone tank. We don't have any suitable space inside the house to locate a tank. Three of the suppliers so far have said we will be fine to locate the water tank outside next to the ASHP if we build a suitably insulated wooden shed structure. One supplier insisted this was a terrible idea and said the tank must be inside the house. I don't know who to believe. I'd welcome input from anyone in a similar situation.

I'll update you all in due course...