Can an Oil boiler be just swapped out for an ASHP?

[pacemaker1000]

My current system is a standard oil boiler heating UFH and HW (300l tank). Although I currently use the immersion for HW with cheap electric and may also use solar. so boiler is currently off and will only be used in winter for heating only.

Boiler flow and return only connection to boiler so can this just be swapped to an ASHP flow and return pipe work?

probably a stupid suggestion but would appreciate comments 

[ProDave]

In principle I would say yes. But a bit more information like age of house and how much insulation, size of heated floor area and what temperature was the UFH water with the oil boiler?

[Fly100]

Remember flow temps from an ASHP are alot lower, so warm up times can be extended. I believe the normal course of action is to increase radiator sizes, as ProDave said it depends on the house really.

[joth]

9 hours ago, pacemaker1000 said:

 so boiler is currently off and will only be used in winter for heating only

To clarify, if you have an ASHP you might want to use it for DHW rather than the immersion as on cheap rate electric the HW will be even cheaper.

 

The trade off is the time the ASHP is doing DHW it's not doing space heating, so if you only have a couple hours cheap rate (Octopus Go?) then it's not clear cut which is the better use for it during that crunch time.

[Wil]

I have done this. Direct swap (for now) in order to get in ahead of the RHI deadline. I was/ am awaiting planning for a refurb so had to jump the gun.

 

It works. It’s probably horrendously expensive. My EPC calls for 62MWh of heat. The HPs (I had to have 2 to cope with the losses) have used 6.8MWh of electricity since early December so at a rough COP of 3 and an estimate of 10MWh of elec for the year I’m up to 30MWh of heat delivered. That includes my HW which during the summer has been entirely solar diversion. I replaced a consumption of around 3500litres of oil so just about stacks up heat wise.

 

As above the HPs are delivering at 45degC, not the 70+ of the oil burner. Rads were massive but full of ancient goo so even after a power flush I’m slowly replacing. Big living room can only just hold temp in deep winter and needs the woodburner to be comfortable. Thermostat set to 19 in the hall.

 

 

 

 

[ReedRichards]

If you have exclusively UFH (I presume wet UFH supplied by your oil boiler) then that should work equally well with an ASHP.  But if you have a standard HW cylinder then the surface area of the heat transfer element (the coil) is likely to be too small so your cylinder will be slow to heat up.  Maybe with UFH that's not so important?  Or if you continue to use your immersion heater it wouldn't matter (but would be more expensive than using the ASHP).   

[Gone West]

13 hours ago, pacemaker1000 said:

probably a stupid suggestion but would appreciate comments

Not stupid, but not something I would do. I am going to replace my 70% efficient old Rayburn with a 90% efficient Grant condensing oil boiler.

[Roger440]

With prices where they are going, oil will be the cheapest form of heating available. Becuase it not linked to the price of gas.

 

I just filled my tank 2 weeks ago, which, happily, was the day it was its lowest before it went back up again.

[pacemaker1000]

Thanks guys. Few answers…

house built 2005 efficiency is C 82

design from company if for 18kw ASHP to include DWH

Direct replacement will mean hot water tank could be used and topped up with immersion by cheap rate or solar so not a priority.

current UFH set at 35-40 I think so not high

only 3 rads in house other 12 rooms UFH

 

if on all day what would it cost once reached temperature?

 

thanks

Edited September 1, 2022 by pacemaker1000

[ReedRichards]

Is your oil boiler on all day?  If you can keep your output water temperature for heating down to 40 C then you might get a SCoP of around 3.5.  So you could aspire to use less than 1/3.5 (2/7) of your current energy demand for heating.  Work out what that is and you can work out what your ASHP would cost to run.  Except that you can't because nobody know the extent to which the government will intervene to control electricity prices.

[pacemaker1000]

Worked out during winter I average 10 litres of oil a day which converts to between 80 and 90 kw a day.

So using 3.5 cop that could be 22-25 kw I think?

so that would at todays prices be £7 for ASHP compared to £10 for oil?

at next month that gain would be lost if I’m right

[Roger440]

4 hours ago, pacemaker1000 said:

Worked out during winter I average 10 litres of oil a day which converts to between 80 and 90 kw a day.

So using 3.5 cop that could be 22-25 kw I think?

so that would at todays prices be £7 for ASHP compared to £10 for oil?

at next month that gain would be lost if I’m right

 

3.5 as an average through a whole winter seems optimistic to me.

 

In which case oil is just about there in being the most cost effective.

 

The good news oil pices are not directly linked to gas. Yes they have gone up, but nothing like the same.

 

Knowing how government works these days i guess extra tax incoming on heating oil.

[pacemaker1000]

Those of us on oil have paid a heavy price for ever.

the thought of it now being the cheapest is quite scary:

[markocosic]

An almost entirely UFH-ed build will be just fine on a heat pump; and if you're peaking at 35-40C input temperature (so can go lower when it's warmer) then sCOP will be excellent. Probably nearer 4 with a good unit and some attention to just how low flow temp can be set most of the time.

 

If oil boiler not stuffed then install in parallel with changeover valves such that you can fall back to oil if required for stoopid cold or stoopid spendy electricity. This might also let you sit below the ~16 kW size where you are over 16A per phase and the DNO needs to be involved.