Changing from oil central heating

lohr500

Reed_Richards said:

The other thing to understand is that whilst a heat pump will be least efficient when it's really cold outside, conversely it will be most efficient when it's not so cold and it's the seasonal average that determines how much your heating costs.  A modern heat pump should give you more than 3 kW of heat per kW of electricity, averaged over the year 

But isn't that where the main problem is? When you want most heat in your house, it is usually very cold outside.
Typically we don't run our heating at all from May through September.

Depending on the relative cost of oil and electricity, we do use oil or off-peak electricity to heat the water in the summer. I guess a heat pump would be more efficient for doing this if a suitable tariff was chosen where the low off-peak rate was not offset by an expensive peak rate.  

wrf12345

I would start by super insulating the house with Celotex insulation on the inside walls and radical downsizing of the windows except for the south side. The next tax year may have new incentives for fitting different types of heat pump so may be worth waiting for that, also there are some separate grants for electric-only houses so may pay to pull all the oil-powered junk out and put some cheap electric heaters in for a short period (after winter, I guess). Electric showers and instant-on electric water heaters are worth investigating if you can minimise use of hot water rather than trying to have huge cylinders of water constantly heated by a heat pump, which would then lead the way to air-air heat pumps which can work well for instant room heat. If your design of house lends itself to just heating the lounge area (or can be redesigned to do so) and letting the bedrooms heat up merely by opening their doors at night, then a singular air-air heat pump may suffice. There will be a lot of criticism of this post by people who can't read whole sentences...

tamste

Don't forget to include storage heaters on E7 in your renewables mix. These use electric only and charge overnight using cheap rate electricity (~35-49% cost of day rate). Modern ones control automatically as they all have their own thermostat 

FreeBear

lohr500 said:

Reed_Richards said:

The other thing to understand is that whilst a heat pump will be least efficient when it's really cold outside, conversely it will be most efficient when it's not so cold and it's the seasonal average that determines how much your heating costs.  A modern heat pump should give you more than 3 kW of heat per kW of electricity, averaged over the year 

But isn't that where the main problem is? When you want most heat in your house, it is usually very cold outside.
Typically we don't run our heating at all from May through September.

Depending on the relative cost of oil and electricity, we do use oil or off-peak electricity to heat the water in the summer. I guess a heat pump would be more efficient for doing this if a suitable tariff was chosen where the low off-peak rate was not offset by an expensive peak rate.  

Regardless of the type of heating you have, it is going to have to work harder when the temperatures plummet outside. Whilst an ASHP efficiency will drop on real cold days, this is offset by higher efficiencies when it is a little warmer. So rather than looking at spot efficiencies,  you need to look at the average figure over the year.

Reed_Richards

Phones4Chris said:

Sorry @Reed_Richards my understanding is that Heat Pumps are not as flexible as other boilers, 

No offence @Phones4Chris but I actually have an ASHP; I have had it for almost 4 year now.  Whilst you only have a neighbour who has one.  Perhaps you can tell me why a heat pump is slower to respond than other boilers?  It isn't; why should it be?  Here are some reasons why you might have this false impression:

A lot of people use heat pumps in conjunction with underfloor heating and underfloor heating, where they pipes are laid in a concrete screed, is slow to respond because of the thermal mass off the concrete, which acts much like a storage heater.

And a lot of heat pumps use Weather Compensation where the heat pump output is matched to the demands of the house under it's ambient conditions.  That can lead to a slow response time but you can disable Weather Compensation if you want to heat a house quickly from cold.

A lot to do with speed of warming is the match between the radiators and the water temperature they are intended to be used at.  Heat pump installers generally try to achieve a good match whereas older heating systems often have radiators that are bigger than they need to be.  Oversized radiators will warm a cold house more quickly but will cause the heat source to cycle more when running under ambient conditions, which can cause wear. 

I used to have an oil boiler but it was an external boiler.  If I wanted to heat my house more quickly than usual I had to undo some screws, remove the top cover and raise the water temperature setting.  Then I had to do the same to set it back to normal when the house was suitably warm.  That was such a faff I almost never did that, and never at all after I got a controller that allowed me to turn the heating on remotely before I got home.     

Phones4Chris

Reed_Richards said:

.................  With a heat pump you can certainly boost the hot water if necessary but as with most other heating systems, when you are heating your hot water you are not heating your house. ................

I don't have that problem with my oil central heating, it can heat both at the same time and often does in the colder months.

Reed_Richards

Phones4Chris said:

Reed_Richards said:

.................  With a heat pump you can certainly boost the hot water if necessary but as with most other heating systems, when you are heating your hot water you are not heating your house. ................

I don't have that problem with my oil central heating, it can heat both at the same time and often does in the colder months.

So you have what is called a Y-plan heating system with a non-combi ("system") boiler.  This means you can only set a single boiler water temperature and this has to be hot enough to heat your hot water cylinder to your desired temperature.  This may reduce the opportunity for your boiler to operate in condensing mode (if it is a condensing boiler) which will reduce its efficiency and so make it more expensive to run.

You would not plumb a heat pump this way because you generally want a lower water temperature for your central heating than for your DHW and this is because the lower the water temperature at which a heat pump works, the more efficient it is.  This is also true for oil and gas boilers but the improvement in efficiency with reduced water temperature is greater for a heat pump.  

Phones4Chris

@Reed_Richards no it's not a condensing boiler and FYI there are oil boilers that can give 90% efficiency without being a condensing variant (my engineer said 55deg iirc), but also iirc you can't install new ones of them now anyway (since 2018?). I believe they have to be condensing now (all for an extra 2% efficiency) the hassle with extra installation work is a pain.
The thermostat on the HW cylinder determines the HW temp and the Room stat obviously room temp! The boiler temp is as low as we want and can turn it up if we need quicker output if things are really cold.

Reed_Richards

@Phones4Chris, according to the Viessmann website, non-condensing domestic oil boilers have not been legally sold since 1st April 2007.  And whilst I suppose you might have been able to find a non-condensing boiler with 90% efficiency back then, the majority were not that efficient.  There were further changes to the regulations in 2018.

But

In rare cases, a condensing boiler may not be a viable option in a particular property. If an assessment carried out by a Gas Safe registered installer suggests this is the case in your home, you may be permitted to get an alternative system.  

"Gas Safe" implies gas, I don't know if the same applies to oil boilers.

HillStreetBlues

This is a good guide if a non-condensing boiler can be fitted https://www.mistralboilers.com/boiler-information/condensing-non-condensing/exemptions/