Back boiler: replace with new gas boiler, electric, or heat pump?

prowla

I have a recently installed solar system, comprising 7x 475W panels, a Fox H1-5.0-E-G2-WL inverter and a single Fox EP6 battery; I'm still waiting for the G99 so I can get onto the Octopus tariff, but meanwhile I'm kindly donating my excess power to the Grid.

It's fine for the Summer (the panels can do up to 4kW), but I'll likely upgrade the setup to include an extra 5 panels to cover charging on dull days (maybe 400W or less) and a second battery to avoid battery anxiety.

For heating (radiators) and water I have an aging Baxi back boiler system with a tank which is probably original to the 1960s house.

Pending the G99 and tariff, I've taken to switching on the immersion heater to warm it when I have a full battery and the panels are still generating excess power; on sunny summer days my gas consumption is just running the pilot light.

On to the question…

Running the old, inefficient (maybe 70%?) back boiler is costing me:

• Standing charge = £0.21/d = £106/yr
• Pilot light = 23p/day = £7.00/m = £84/yr
• British Gas Service contract = £40.25/m = £483/yr
• Tot = £673/yr (£567 exc standing chg)
• My gas consumption ranges £40- £110 per month over the seasons.

I'm now looking at options for replacing the boiler and am considering the following:

1. Simply replacing the gas boiler with (eg.) a Worcester Bosch 4000 and keeping the rest of the system; this would eliminate the pilot light and the service contract and also be 25% more efficient, this could be a saving of ~£750/year against a ~£5000 outlay.
2. Going for an A2A heat pump for heating/cooling and replacing the gas boiler with an on-demand electric one. This would eliminate gas completely, saving ~£900/year, but would cost ~£9k plus the operational cost of the new setup.
3. Getting an A2W heat pump for heating and water. Again this would eliminate gas and save ~£900/year, but the cost after grant could be ~£7k and siting the outdoor unit may be an issue.
4. Just going electric using solar and pulling from the Grid as needed.

I'll be getting some quotes on the options.

Which should I go for???

QrizB

My initial thought:

Just going electric using solar and pulling from the Grid as needed.

Don't do this.

I don't know exactly how much gas you're using (as you haven't said) but switching from a 70% efficient boiler to direct electric heat will cost you something like 2.5 times as much in fuel.

How I calculated this:

• Ofgem capped rates from July: gas 7.33p/kWh, electricity 26.11p/kWh
• Cost of a kWh of heat from gas burned in a 70% efficient boiler: 7.33 / 0.7 = 10.47p
• Cost of a kWh of heat from electricity in a 100% efficient heater: 26.11p
• Increase in costs from switching from gas to electricity: 26.11/10.47 = 2.49 times

Your £40-110 per month spent on gas will become £100-275 a month spent on electricity.

QrizB

Next thoughts:

• Have you had a quote for a new gas boiler? £5k seems quite a lot?
• Have you had a quote for A2A and an electric boiler? £9k seems quite a lot too?

FreeBear

You make no mention of the type or size of house…

I have a (fairly typical) late 1920s 3 bed semi that had a Baxi back boiler up to a couple of years ago. Before it was replaced, I had fitted smart(er) controls that allowed me to set a different temperature based on time of day. That helped to cut gas consumption by about 10%. During the summer months, I also turned the gas off so that the pilot light wasn't permanently on.

Never had a BG contract. Instead, had a service as and when needed. Fell out big time with the last company when they slapped an At Risk notice on the back boiler because it was "missing" a grommet around the thermocouple. Baxi do not list this mythical grommet in the spares list, and no such thing is available from any spares supplier… Eventually found another engineer that understood this point and was prepared to complete the service and remove the AR notice. Be careful if BG tries to pull the same stunt.

When I eventually replaced the Baxi, I took the opportunity to completely replumb the heating system and fit larger radiators throughout the house. Radiators got moved to internal walls (with decent double glazed windows and plenty of loft insulation, having radiators under windows is not necessary). The pipework and radiators were all specified with a heat pump in mind. But at the time, one of the requirements of the BUS grant was that EPC recommended upgrades also needed to be done. That took the idea of a heat pump well over budget. The following year, this requirement was dropped and I could have had a heat pump installed for about £3000. Should have waited, as the gas combi that I had installed (plus the replumbing) came to about the same price.

In your shoes, with solar panels and batteries, an A2W heat pump would be my recommendation. I'd also take the opportunity to replumb the system (if you have pipes buried in concrete, I'd upgrade that to a must rather than a recommendation). Gives you opportunity to rationalise pipe layouts & radiator locations. I'd also look at relocating the hot water tank if possible.

Should you decide to go for a gas boiler, I'd still recommend a replumb & bigger radiators - It will allow you to run at a lower flow temperature which gives a much higher boiler efficiency. I run mine at 50°C for much of the time and have cut gas consumption from 8000kWh with the Baxi down to 3200kWh with a Viessmann 050.

Oh, and if you go with a gas boiler, don't stick it in a garage or loft. When running, some 6% of the heat is lost through the casing. This "wasted" heat can help to keep the house warm if it is within the envelope of the building. I have mine in the hallway for just that reason.