Your renewable heating system must be installed and commissioned before you apply, the paperwork should not hold up the installation. The deadline for applying is 31st March 2022. An install on average takes 3 days depending on complications, mine took 2 days. There is a big demand for heat pumps at present so finding an installer to fit before the deadline might be difficult. You should not need planning permission if your pump is MSC certified. Electricity prices are high at present with no indication that the prices will go down in the future.  There are indications that gas prices will go up considerably so looking at alternatives may not give you a price advantage in the near future. You are off-grid for gas so that would be a gas or oil storage tank which is still not cheap to install. 

He's talking a fair bit of rubbish here but the short answer is I think you'd be very lucky to get one in and RHI approved by then due to the lack of installers. It took us about 6 months or so from picking up the phone/emails sent to getting RHI approved, as pretty much everyone was mega busy and it was an intensely frustrating process with multiple installer no-shows for quotes etc.

However, the timeline from installation completed to RHI was really very short indeed. We had a lot of little niggling issues with our installation which delayed my final payment and consequently the RHI paperwork, but the MCS paperwork was received about a day after my final payment, I applied online a day or two later and the RHI was approved instantly. So - if you had a good installer ready to go and happy to get the paperwork done quickly too, I think you could get it turned around before then. But - my own experience is that getting a good installer is about the most important thing you can do - there are plenty of horror stories on here and elsewhere of bodged installations that should caution you accordingly. There are lots of good installers too and you have to go into it with your eyes open - if you are being promised the earth and it doesn't feel right then just keep looking rather than go with a bodger just to get RHI. The new grant thing from April is still pretty reasonable (£5k) and all up front as opposed to spread over 7 years.

As to the financial viability of it all, that is a difficult one to answer - it works for us and I only know 3 other friends with ASHP but I think it's fair to say we are all either very happy or reasonably happy with the financial viability. We are on an expensive tariff, are very heavy elec users anyway and our bills have only been marginally more than we paid before, without the expense and hassle of chopping 12-15 tonnes of wood a year on top (roughly £1000+heaps of time). From Nov and into Dec the bills have gone up quite a bit, but even so it is still only £70-80 more in Nov and likely £100 more in Dec than before. So, overall I expect 6 months a year where there is negligible elec cost increase (was actually less than before in Sep!) and 6 months a year where there is a variable increase from £70/month to maybe £150 month more...average it out it becomes quite reasonable. My elec DD is set to £250 when it was around £150-180 before the ASHP on much cheaper elec; I think it will settle at £200-230 or so over the year.

On top of that we are receiving £140/month (£11.2k) RHI for the next 7 years.

@andygo, I think it'll be touch and go if you make it. In our case, we received all the required RHI registration paperwork from our installer within two days of the system being commissioned. We then applied online and it took the RHI ages to process our application, but the important date is when the system was finished and commissioned and that must be before March 31, 2022.

What frustrated and delay us was the DNO approval. We are managed by Scottish Power – I think their maximum response time was 180 days and they literally ran the clock down to that timeframe, which delayed us massively because everyone else was good to go. Find out who your DNO is and how long they give themselves for approvals.

@siko @editor Thanks for the responses. We're considering going for the lower of the silly quotes (£11.6k for a 7kw aroTherm plus). Trouble is they don't have any stock so installation wouldn't be until around mid/late Feb. That will leave just a month to make sure RHI is approved. We think we'd get around £8k back so it's pretty vital to make the March 31 deadline...the replacement £5k grant wouldn't be enough to make the figures work for us.

Also the installer who told me it's too late also claimed the new £5k grant system will be means tested - who knows...

Our DNO is Western Power. The installer said they would take care of that but I'll give WPD a call to check their timescales. 

Still fear the rising electricity costs, but then we don't really fancy any of the alternatives.

Octopus installed a smart meter for us, but they can't get it to work (poor reception area) so at the moment we're stuck on 24p kwh. 

Our plan is to install alot of PV, which though useless in winter, will hopefully offset some of our electricity bill in summer.

This whole thing is really stressful...

@andygo It took us just over 3 months from the first phone call to get a quote to having the system installed and commissioned.  But it was a very stressful process, which involved lots of chasing.  Everyone is busy so you do have to keep pressing the urgency to keep things moving.  We received the MCS certificate 2 days after commissioning.  I then applied for RHI that evening and it was approved online immediately.  Our first payment is due in February.

We have just had an Vaillant Aerotherm Plus installed and approved RHI.  It took from around July to now, December.  I also needed planning as it is the larger twin fan unit, remortgage the house, replaced consumer unit as no spare ways.  New EPC, builders work.  Further electrical work to install supplies etc etc.   There are ASHP supply problems certainly and installers will be booked up.

Painful at times but the pain is over and the ASHP is great.  Solar and battery next.

Overall realistically I think you will be lucky to get one in before the end of March.  

Worth getting one still in my opinion, it's a long term investment but you may need to re-evaluate, don't give up!  I think the cost of electricity absolutely has to have the carbon taxes shifted off it or the governments domestic decarbonisation plans are dead in the water as no-one will change over and it's not a walk in the park retrofitting.