The high temp is only used for the legionnaires cycle and the rest of the time it should be in a system designed to be below 45 and mostly ~30C. I can see why you want to use an immersion in order to not load the pump too much.

The problem you’re going to have when firming up on quotes is that (I believe) the MCS rules say your ashp has to provide all the heat, making no allowance for stoves or Agas.

Since you have scope to change your house design perhaps you could add even more insulation (including the floor of course and reduce your heating needs. UFH is very useful in complete refurbishing because it can (indeed often must) run at lower temperatures.

Thanks for the reply Judith.

I didn't realise that the ASHP has to supply the hot water to qualify for the grant. That may change things...

Is it possible to dictate how much of the hot water heating is done by the heat pump and how much is done by an immersion, say at night. I don't want to jump to the two heat pumps scenario just because on the occasional cold night a single 14kw pump won't be able to supply adequate heating AND hot water. At those times I would rather tell the heat pump to supply heating only and let an immersion take care of the hot water overnight.

Colin

@ccap FWIIW, Our DHW is handled by a Sunamp Thermino ePV210 unit; this heats the water using solar energy from our PV arrays, or it can take power from the grid (we have a MyEnergi Eddie). The Daikin ASHP supplies all the space heating and we applied for and received the BUS grant. This was all approved through MCS by our installers. When I received a follow-up call from MCS and they asked if the installation supplied our hot water, I was able to confirm it did; both DHW and space heating formed components of one installation. I hope that may help you assess your situation. Regards, Toodles.

@ccap just to give you some rough comparisons, I have a Samsung 12Kw HT Quiet unit which most of the time produces a flow temperature in the 30C range for heating. Running the unit in this range produces (in my case) adequate heat for the building without working the pump too hard. The result is a very quiet (at lot less than my oil boiler) operation.

During the night the heatpump heats my 200L DHW cylinder to 55C and uses on average 2Kwh - 2.5Kwh of electricity. This requires the heat pump to raise the flow temperature to approximately 63C - 65C to achieve this. The heat pump noise is a little louder but still well below my oil boiler sound level.

In the case of the Samsung (and most other heat pumps I know of) it can only be in heating mode or DHW mode at anyone time not both together

Regards

Thanks, it's good to hear about real world experience with the product I may end up going with.

Can I ask why you still run the oil boiler when the outside temperature drops? Is this working out cheaper for you, or will your setup simply not keep the house warm enough without the boost from heating oil?

Thanks

@ccap running my oil boiler is just a personal choice for me. My heat pump is physically capable of heating the house to about -6C OAT before it will start running out of steam, based on my heat loss calcs.

The reason for running the oil boiler in a bivalent set up is when the outside temperature goes below a certain point (+4C at the moment but I adjust this depending on the cost cross-over point) it is cheaper to heat the house with oil sadly. With high electricity prices currently and volatile oil prices I run whichever is the cheapest at the time. In addition the oil boiler is a very high efficient model and is only 6 years old so seemed a waste to scrap it.

My longer term plan is when or if electricity prices come down to such a level that I am using the heat pump all the time, I will decommission the oil boiler but while we are in this transition period I am keeping my options open.

Regards

Makes perfect sense!

@technogeek Realistically priced electricity is well overdue in my opinion and can’t come too soon! Regards, Toodles.

Hi Coli, @ccap Are you planning to apply for the BUS £7500? If so you have to follow the MCS rules which mean any fossil fuel heating must be removed (no hybrid operation as @Tecknogeek describes above, which was allowed in a previous scheme) and the heat pump must supply all of your heating and dhw, (all of the building and no supplementary heat sources).

If in the scale of your refurbishment the £7.5 is worth less than getting what you truly want and need then ignoring the BUS is worth considering. You’ll then need planning permission but you’ll be doing that anyway

One of the answers to your original question is that the high temperature pumps are the more modern ones and they put lots of effort into making them quiet too.

For a total refurbishment do consider an MVHR system it’s the only time that it is sensible to fit one since the pipework to ever room is 100/150mm in diameter.

Thanks for the input. I believe that I can have a wood burning stove as long as the heat pump is capable of supplying heat to the whole house, so I have done the calculations based on a slightly lower room temperature in the room where we'll have the burner. Same for the Aga. The average temp assumed over the whole house is still about 19 or 20 degrees, which is perfectly reasonable I think. 

BTW the irony of putting all this effort into an efficient, modern heating system and then bunging in an Aga is not lost on me! We're planning on getting an old electric storage model that is filled with bricks like a night storage heater. We heat it up over night on the cheap EV tariff and hopefully it doesn't cost us an an arm and a leg. It's a non-negotiable with my wife unfortunately! We've had both gas and oil Agas before and although expensive to run, the way I look at it there's no heat wasted, it just warms the kitchen and the rest of the house as well as dinner!