Bivalent ASHP and oil boiler

matt_drummer

QrizB said:

If you think you need plumbing improvements to make use of a heat pump, won't you need those same improvements anyway if you plan to run a heat pump in parallel with your oil boiler?

By keeping the oil boiler, you still have the ongoing maintenance costs and an oil tank in your garden that you'll still worry about running low / out when you need it. And you won't qualify for the £7.5k boiler upgrade scheme grant. Plus, if you fit an undersized HP just to supplement the boiler, you'll need to replace it again when you finally give up on oil.

I might be missing something, but I don't think you've made a clear case for keeping both - other than redundancy.

You are quite right.

I think the only reason for having both would be if you lived somewhere so cold where a heat pump couldn't cope at the extreme cold weather and the back up of an oil or gas boiler is necessary.

Everything else you say is correct too, chose one or the other, having both is a silly idea.

matelodave

As I suggested earlier on, do it properly and then you'll only have to do it once,

greenbee

I've already said I don't qualify for the boiler upgrade scheme grant. And no, with a bivalent system I don't need to upgrade the pipework immediately. I'm also not sure where you got the idea that I'd fit an undersized ASHP. But don't worry, if it is undersized for the house as a whole, when we come to upgrade I'm sure it can be used to heat a swimming pool. 

I'm not looking to make a financial case based on getting a grant. I think I made clear from the outset that this was about resilience and redundancy - so it's reassuring that you think I've made the case for that, as that was my concern. 

greenbee

matelodave said:

As I suggested earlier on, do it properly and then you'll only have to do it once,

But as I've explained, that means replacing all the pipework and radiators at once. Not something I either want to or can do given that I work from home and major work like that would involve taking up the floor in every room -  not something I want to do again while trying to hang on to both my job and my sanity. It would effectively mean getting the contents of the house packed up and put in storage, renting another place to stay and work until the works were over AND somehow overseeing the work. I've already been through what's involved with the heating engineer. 

It may cost more in the long term, but it'll be easier to cashflow some of the funds And the heating in each room will be upgraded as other work on it is being done. When my office is being done I can work in the soundproof cell I used for video and audio work - which will be done when there is a gap in my recording and broadcasting schedule. Noisy work will mean rescheduling of recordings to outside UK working hours, and all the equipment needs to be protected from dust. 

TBH, I'm not sure why I feel the need to justify myself here - but the financials aren't what I was asking about. I was hoping I'd find someone with experience or knowledge of bivalent systems, which hasn't happened. Luckily we've found them elsewhere and we'll be working through some of the questions, ideas and issues over the next month or so. 

QrizB

greenbee said:

I'm not looking to make a financial case based on getting a grant. I think I made clear from the outset that this was about resilience and redundancy - so it's reassuring that you think I've made the case for that, as that was my concern. 

That's fine then.

Fit a direct electric boiler. You'll save maybe £5k on the installation cost compared to an ASHP.

Let's imagine electricity remains 30p/kWh. With a direct electric boiler, each kWh of heat will cost 30p. With a heat pump and a 3:1 COP, each kWh of heat will cost you 10p.

At 20p/kWh extra, you'll rech the £5k cost of the heat pump after buying 25000kWh of direct electric heat.

Let's also imagine you only run out of oil in the depths of winter when you need 200kWh of heat a day (a lot, 20 litres of oil worth). 25000kWh of electricity will last you 125 days. That's four straight months of however-cold-it-is.

Put another way, if you need to run it for a week a year, it'll be thirteen years before you've spent more on electricity than you saved by buying a direct electric boiler.

FreeBear

greenbee said:

Overall just using the heat pump probably would cost less BUT the cost (and disruption) of upgrading all the pipework and the radiators needs to be taken into account. So it isn't entirely straightfoward. The boiler should, if looked after properly, last a while longer - and hopefully by the time it needs replacing, most of the work needed to upgrade the heating will have been done - because as each room is renovated we will upgrade.

Replacing a few radiators room by room is possible as you renovate each one. But if you intend to move the radiators and/or make drastic changes to the pipework, you may well find it easier to do it all in one hit. Saves having to lift flooring multiple times to do the work.

Renovating here on a room by room basis. Bit the bullet on the heating system earlier in the year and replaced most of it in one go. Figured it would be easier to manage a few days of disruption across the whole house over a short period. But I'm fortunate in that the CH system is fairly simple and I don't have the complexity of zoned areas or underfloor heating.

greenbee

FreeBear said:

greenbee said:

Overall just using the heat pump probably would cost less BUT the cost (and disruption) of upgrading all the pipework and the radiators needs to be taken into account. So it isn't entirely straightfoward. The boiler should, if looked after properly, last a while longer - and hopefully by the time it needs replacing, most of the work needed to upgrade the heating will have been done - because as each room is renovated we will upgrade.

Replacing a few radiators room by room is possible as you renovate each one. But if you intend to move the radiators and/or make drastic changes to the pipework, you may well find it easier to do it all in one hit. Saves having to lift flooring multiple times to do the work.

Renovating here on a room by room basis. Bit the bullet on the heating system earlier in the year and replaced most of it in one go. Figured it would be easier to manage a few days of disruption across the whole house over a short period. But I'm fortunate in that the CH system is fairly simple and I don't have the complexity of zoned areas or underfloor heating.

The heating here is a mess, which obviously complicates things! And… we’d have to get the entire house packed up as every floor would need to come up and be replaced so there would be nowhere to put stuff, or live, or work. Some of the downstairs floors are tiled. And all upstairs is hardboard not floorboards. In the last house we moved the pipe work out of the floors downstairs and had it all running under the first floor which made life easier after it was done. But getting it done was miserable. 

I’m hoping we can deal with the plumbing in the same order as the electrics (also a mess) which are being planned at the moment based on minimising disruption. 

Reed_Richards

The heating pipes in my bungalow were under the floor but embedded directly in the screed with no protection; something that had been done 40 years previously.  We relocated the pipework to the loft when the ASHP was installed.  

greenbee

Reed_Richards said:

The heating pipes in my bungalow were under the floor but embedded directly in the screed with no protection; something that had been done 40 years previously.  We relocated the pipework to the loft when the ASHP was installed.  

Very sensible. I'm hoping I won't find that's the case here - but as the electricians are doing the rooms roughly in pairs (up and down) then if they are, we can shift the pipework up as we go. In the spring or summer when it's not cold!

While I didn't want a project this time, at least that way I ended up knowing exactly what was where and how it was done last time...