Do you want to keep your radiators? Are you happy to replace with low temperature radiators, or keen to get rid of them altogether?

 

Happy to keep the existing radiators as I assume that’s more cost effective than replacing them all. Happy to be corrected.

 

The issue with keeping existing radiators is that heat pumps inherently become less efficient the higher the temperature they have to operate at. If your existing radiators were sized to work at a temperature of 70C, they won't be very effective at 40C. And for best efficiency you might even want to try and get that down to 35C or so. Bear in mind that whether ground, water or air source the source temperature is unlikely to be much above 8-12C, 16C at best on a spring or autumn day with an air source heat pump when you want just a wee bit of heating.

So in summary heat pumps work most efficiently with "low temperature" heat emmiters - either specialised low temperature radiators or underfloor heating (or perhaps "thermaskirt").

Personally I looked at various alternative options that might qualify for the RHI, but ended up installing Air-to-air heat pumps instead, even though they don't qualify for the incentives. They're more efficient and (much) cheaper to install, especially as a replacement for the storage heaters we used to have. And it means I don't have to have radiators taking up wall space. They don't do anything to provide hot water though, so that stays as an immerser heated tank, for now, but with a "solar diverter".

Is your 9kW system single phase, or three phase? Mine unfortunately is three phase, which makes finding a diverter that will make best use of the generation a bit of a pain, since they're inevitably single phase, so we don't get the best use out of it.

 

I’m single phase.

Thanks for the reply.

I have a 4 bed detached house. Would I need to get new heaters in each room. Sounds expensive.

 

I’m single phase.

Thanks for the reply.

I have a 4 bed detached house. Would I need to get new heaters in each room. Sounds expensive.

One (cheaper) possibility if your boiler is still in decent nick would be to keep it but add an Air-to-air heat pump or two to provide background heat and so reduce how often you need to run the GCH.

 

Have done it, if you want grant you need a registered installer. Get an energy assessment who will confirm if you need any insulation before being eligible. Look at fitting underfloor insulation to suspended floors, you will probably have to have cavity wall insulation fitted. We have solid walls and I added 50mm cellotex to many of the walls internally.

We had new radiators throughout, a huge 250l hot water tank, 100l buffer tank and a Stiebel Eltron WPL 25A heat pump, from a 40 year cast iron boiler.
WPL 25 A Air | water heat pumps of STIEBEL ELTRON

Used about 25,000kWh of gas last, year now about 6,000KWh of leccy up from 2,500kWh but with some for the car and supply from a 3.6kW solar system. Works brilliantly. Hard work, takes up loads of space but I would not go back.

More info if you want it.

 

Have done it, if you want grant you need a registered installer. Get an energy assessment who will confirm if you need any insulation before being eligible. Look at fitting underfloor insulation to suspended floors, you will probably have to have cavity wall insulation fitted. We have solid walls and I added 50mm cellotex to many of the walls internally.

We had new radiators throughout, a huge 250l hot water tank, 100l buffer tank and a Stiebel Eltron WPL 25A heat pump, from a 40 year cast iron
Used about 25,000kWh of gas last, year now about 6,000KWh of leccy up from 2,500kWh but with some for the car and supply from a 3.6kW solar system. Works brilliantly. Hard work, takes up loads of space but I would not go back.

More info if you want it.

I would be grateful for more info. Am considering a similar upgrade to our heating. Who did you use as installer?

 

Cost us about £18k, much cheaper than moving as an option and we get RHI payments over 7 years of £10,600, so the system will then have cost about £7k.

Be cautious of systems and how they cope with cold weather, we have a system that has adequate reserves, it does not need to use resistive heating for water nor for de-icing, all of our heat has been from the heat pump element. This heat pump is also very quiet. It is set up to heat up water at midday rather than during the night so that the air temperature is highest then and our solar is generating maximum power.

Installer Search - Microgeneration Certification

Installers here.

 

40 year old boiler just means it was a decent solid cast iron job with minimal electronics. Will probably last forever with minimal TLC and replacement of a few minor items like thermostats.

Suggestion to supplement with air to air heating really is very sensible way forward and will give much better COP than trying to heat water and use old radiators.

 

40 year old boiler just means it was a decent solid cast iron job with minimal electronics. Will probably last forever with minimal TLC and replacement of a few minor items like thermos

I agreed with this for a long time, but the pilot flame kept running and we used more gas than others. Our insulation has helped but moving to ASHP has been very successful.

 

My "40 year old boiler" is only fired up about 10 times per year. So the pilot supervision thermostat has an off switch with a good clean snap action, toggle switch, silver contacts. I turn it back on and relight the pilot for the very rare occasion its needed.

 

Suggestion to supplement with air to air heating really is very sensible way forward and will give much better COP than trying to heat water and use old radiators.

COP, from ASHP

DHW - this year we have generated 2.045MW of hot water for 0.445MW of power
CH - 12.419MW of heating for 1.925MW of power

Total power used is 3.644MW from meter includes pumps, controls etc.

Not sure how you get a better COP?

During the summer the ASHP heats the water at midday, on sunny days the solar panels have plenty of power initially and only need a top up for the final heat pump at 50c. During the winter, wind is the power source via BULB.

Gas is gas, how much longer do you want to burn gas, I have given up with it.

 

So whats the cost of an air-to-air heat pump for an insulated 4 bed house? To eliminate 90% of gas use?

 

It won't eliminate 90% of your gas use, especially if you need to use gas to heat your hot water, but this should put a dent in your heating requirements:

Daikin Air Conditioning FTXM25M Wall Mounted 2.5Kw 9000Btu Inverter Heat Pump R32 A 240V 50Hz

Works well with PV, and can even give you some "free" cooling if installed with such.

 

How much is installation an can i diy install?

 

No to that one. Installation should be around £600-800 (probably +VAT). If you have it downstairs in the lounge or hall and keep doors open to allow the heat to "spread" you can switch off your heating a bit earlier in the spring and on later in the autumn, and even in winter it should reduce how much gas you use. If it's particularly cold outside you can switch back to just gas (although CoP is probably still worthwhile even then). As you say, you'd have to turn down the lounge radiators and probably relocate the thermostat - and/or switch to something like individual "smart" TRVs (something like the Evohome or Tado), which are probably worthwhile anyway..

 

I think i could put this in the lounge and some of the heat would go upstairs as well. I'm assuming it needs to be on an extenal wall? Maybe switch off the GCH radiators in the lounge and move the themostat to a bedroom upstairs?

 

Sorry. Hat does cop stand for?

 

COP, from ASHP

DHW - this year we have generated 2.045MW of hot water for 0.445MW of power
CH - 12.419MW of heating for 1.925MW of power

Total power used is 3.644MW from meter includes pumps, controls etc.

Not sure how you get a better COP?

During the summer the ASHP heats the water at midday, on sunny days the solar panels have plenty of power initially and only need a top up for the final heat pump at 50c. During the winter, wind is the power source via BULB.

Gas is gas, how much longer do you want to burn gas, I have given up with it.

Something odd about those COP you imply based on the raw numbers. Care to give some more details of how you measure thermal output to water, eg instruments for measuring flowrate if water and delta TS. What temperature do you set the DHW storage to.

Could you provide a sample instantaneous calculation for say a 5 degree C 85%RH winter day.

 

Something odd about those COP you imply based on the raw numbers. Care to give some more details of how you measure thermal output to water, eg instruments for measuring flowrate if water and delta TS. What temperature do you set the DHW storage to.

Unfortunately the data from the Stiebel Eltron ASHP is very limited, those figures are from the data that it collects and represents a year use, it was installed a year ago. It does not provide data for previous days.

For a years DWH, set to 50c at mid point in the 250l tank, so the top gets to about 55c, we used 2,045kWh of DHW from 445kWh of heat COP 4.59, and CH of 12,419kWh of heat for 1,925kWh of power COP 6.45, CH temperature is variable, about 30c when outside is 15c, 40c when 0c.

Please note that our heat pump is by a west facing wall and during the summer the DHW is heated when the air temperature is 24c and the heat pump is working in full sunshine. This is much more efficient than a GSHP which would still be stuck with heat at 8c. Even the CH we need is frequently above 8c. We do not run it during the night very much when the air is cold and have it set to be most active during the day with increased air temperatures.

I accept that there is a significant additional power requirement outside of the ASHP unit, so this registers a power use of 2,500kWh, but on the meter for the total installation we used 3,640kWh.

 

COP coefficient of performance,
1kW of power gives 5kW of heat so COP is 5, does not include peripherals like circulating pumps and control panels.

You are now getting different opinions and you need to work out what is best for yourself. If you have space in a garage or utility room for DWH tank and a buffer tank - great.

If you just want a partial solution too top up Air to air may work, if you want DHW cheaply ( we get 2kW of hot water for 0.5kW of power and much of this is solar) then a ASHP is best.

Some ASHP require resistive heating (1kW for 1kW) to defrost and for some DWH. If the heat pump is not larger enough, some people have use incorporated resistive heating to top up. We have never used this except when an engineer switched it on, I changed back quickly.

" Doing so will be challenging, said the Committee on Climate Change, meaning the end of petrol and diesel cars and gas boilers, " yes, gas boilers should be history. Personally I eliminated petrol and gas last year.

 

Thanks. I have two sales people visiting me today to provide quotes. I’ll stick them on here to get feedback.

I have a hot water tank already. Would I need another one?

My current system is as follows;

1) Hot water radiators in every room. 14 radiators in total.
2) Gas boiler in the laundry room
3) Hot water tank in the airing cupboard
4) Cold water tank in the loft
5) I have a gas fire in the lounge but this rarely gets used. Maybe at Christmas
6) We have a gas hob in the kitchen
7) We have a hive system to control the hot water and heating.

Do all the options mentioned have grants? Also I’ve checked the following link and the two people coming today are not on it but are saying that I’m eligible for a grant Installer Search - Microgeneration Certification

 

As noted earlier, A2A systems don't get any grants and also don't heat your water. But they do have very good CoP (efficiency) and are relatively cheap to install.

I have three A2A units to provide all the heating for my large-ish "bungalow" (which has a lot of roof and outside wall area to lose heat from), with a log stove in the lounge to provide top up heat in the winter. Back when we had storage heaters we used about 25-27000 kWh per year. Now, with the heat pumps and PV, but also with an EV to charge overnight, we're at about 12000kWh.

Note we have no gas at all, so those figures cover everything - heat, light, cooking, TVs and computers! I'd highly recommend an induction hob next time it needs to be replaced - superior to a gas hob in pretty much every way.

 

As noted earlier, A2A systems don't get any grants and also don't heat your water. But they do have very good CoP (efficiency) and are relatively cheap to install.

I have three A2A units to provide all the heating for my large-ish "bungalow" (which has a lot of roof and outside wall area to lose heat from), with a log stove in the lounge to provide top up heat in the winter. Back when we had storage heaters we used about 25-27000 kWh per year. Now, with the heat pumps and PV, but also with an EV to charge overnight, we're at about 12000kWh.

How much did this cost you to install?

 

Our new hot water cylinder is huge 1,800x800mm, buffer tank 900x550mm, 2 x pressure vessels, 3 pumps, control panel. No need for old cold water tank. We used to have electric shower due to imbalanced water pressure, now have an easy thermostatic shower valve with flowing shower.

 

ASHP are quite restricted in where they can be placed, in typical urban environments there may be placement issues, there are then a smaller number of units that are very low noise and are less restricted. We ended up in this situation, but the WSP 25 is very quiet, efficient and when set up correct has no need for resistive heating, all heating, CH and DHW + defrosting (using the buffer tank) is via heat pump function.

Ours fortunately was west facing.

 

No to that one. Installation should be around £600-800 (probably +VAT).

Why do you say that? There are loads of videos on youtube of DIY mini-split air conditioner installations. It looks fairly doable. With such a low input power you could just plug it into an existing socket.

 

I may be wrong, but I'm pretty sure there are regs which forbid you from working on them if you don't have the right qualifications. There are "DIY" installable mini-splits, but they use specific connectors designed for that. They're not keen on refrigerant gases (with high Global Warming Potential) being leaked into the environment by amateurs.

 

Both sales quotes I got were for air to water systems.

Both suggested replacement radiators and a water tank.

One person said I needed to replace my pipes as they were too thin. The other didn't think it was an issue and would have some extra equipment that negated the need for this.

The quote from the person suggesting the pipes needed replacing was approx £18,000 and from the one without was £15,000. These are estimates and they did say I'd have to have a survey to get an exact price.

Both suppliers recommended against air to air. They said there was no grant and the systems were significantly more expensive.

Appreciate any feedback.

 

Both suppliers recommended against air to air. They said there was no grant and the systems were significantly more expensive.

If they were plumbers, I'm not surprised. As noted, my heating (but not hot water) using A2A cost me about £8k. Substantially less than an A2W system would have. And the CoP is better (notionally 5.9 according to the specs). Indeed there is no grant, but I preferred the idea of a more efficient system - I was after all trying to be "green" (and save some on running costs). Add to that the fact that I'm not overly keen on radiators taking up wall space and it was an easy choice for me. They may have thought you meant a ducted warm air heating system, which probably would be both expensive and messy to retrofit thanks to the need to put in ducting all over the house - not something I would recommend!

If we had a house full rather than just the two of us, maybe I would have chosen differently, since the only A2A unit in the "bedroom wing" is in our room, the others have to get by with using the old electric convectors for a top up, when in use, but are closed off most of the time.

I still think an A2A unit or two makes a great supplementary heating system if you already have gas heating.

 

What ASHP are they fitting? Most of my old pipes were fine but still needed considerable pipe work to get the system installed. What DHW tank / buffer tank did they talk about or just basic talk?

If there are plumbers, then they will go for air to water, other suppliers who are not strictly plumbers may talk about air to air, very different installations, good for new build but not easy for refit, unless combined with a ventilation system.

Did they show where the units would be fitted, is that ok? Any idea how pipe work will be installed? This can be troublesome and you may need 2 or 3 isolation switches fitting, can be well hidden or glaring. A lot of space is needed.

 

If you do look at A2A, make sure it's an R32 unit, not R410A (refrigerant type)

Why is this? I read that the "easy install" ones were all R410A. Does it follow that R32 is more toxic and can't be put in the hands of an amature but maybe gives better performance COP?

 

R32

R407c is a blend of R32, R125 and R134A refrigerants, whereas R410A uses R32 and R125, which enables it to operate at these higher pressures.

However R407c and R410a are known as greenhouse gases and are partly responsible for the greenhouse effect on the Earth. In 1999 the Kyoto Protocol on global warming listed HFC refrigerants that were contributing to global warming.

This in turn led to the introduction in Europe of the F-Gas Regulations and at the start of January 2015, the next stage of the F-Gas laws was introduced which detailed the phase down of HFC refrigerants.

It’s important to note here that this is a ‘phase down’ and not a ‘phase out’ – with the regulations now based on the tonnes of C02 equivalent of all refrigerants sold or traded in Europe.

Why R32? Why now?We need refrigerants with a low global warming potential

R32 Infographic


Download here
Each refrigerant has a Global Warming Potential (GWP) with carbon used as the base. Carbon has a GWP of 1.

R410A has a GWP of 2,088 meaning that if one kilogram is released into the atmosphere it would have 2,088 times the harmful effect of one kilogram of carbon.

That is why we are now seeing a move to a new refrigerant – R32, which has a GWP of 675 (two-thirds less than R410a).

The decision by air conditioner manufacturers to transition to a new refrigerant is driven by many factors such as impact on the environment, energy efficiency, safety and cost-effectiveness.

There is a diversity of low GWP refrigerants available to select from. These include HFC 32 (or R32), HFO 1234yf and HFO (hydrofluoro olefin) blends, Ammonia (R717), Propane (R290) and C02 (R744). Unfortunately, none of these candidates is a perfect refrigerant when assessed across the 4 key criteria of

- Environment

- Energy

- Efficiency

- Safety and Economy

Each refrigerant has strong and weak points, which also vary depending on the type of target product. Many major air conditioning manufacturers have determined that R32 is the optimum choice for use in their products because of the following benefits:

The benefits of R32

• Has a low GWP (675)
  
  
  
• Has zero ozone depleting potential (ODP)
  
  
  
• Is ideal for the next generation of equipment
  
  
  
• Offers higher efficiency and longer pipe runs
  
  
  
• Is F-Gas phasedown compliant
  
  
  
• Requires less refrigerant volume per Kw
  
  
  
• Is affordable and readily available
  
  

R32 is a single component refrigerant, meaning it is easier to reuse and to recycle. It is also relatively inexpensive to produce, is easier to handle because it doesn’t separate and utilises familiar technology, keeping costs similar.

R32 is also low-toxic, is difficult to ignite and does not explode.

Why you need to change to R32 refrigerant now

 

If they were plumbers, I'm not surprised. As noted, my heating (but not hot water) using A2A cost me about £8k. Substantially less than an A2W system would have. And the CoP is better (notionally 5.9 according to the specs). Indeed there is no grant, but I preferred the idea of a more efficient system - I was after all trying to be "green" (and save some on running costs). Add to that the fact that I'm not overly keen on radiators taking up wall space and it was an easy choice for me. They may have thought you meant a ducted warm air heating system, which probably would be both expensive and messy to retrofit thanks to the need to put in ducting all over the house - not something I would recommend!

If we had a house full rather than just the two of us, maybe I would have chosen differently, since the only A2A unit in the "bedroom wing" is in our room, the others have to get by with using the old electric convectors for a top up, when in use, but are closed off most of the time.

I still think an A2A unit or two makes a great supplementary heating system if you already have gas heating.

How does the a2a system work. Do you need to have a separate unit outside for each heating unit inside?

Or do you have just one unit outside. Om guessing you still need pipework from the outside unit to the inside units.

Can you share some pics of the outside unit, inside unit and pipe work to help me get a feel for this option?

 

How does the a2a system work. Do you need to have a separate unit outside for each heating unit inside?

As usual, "it depends". The units I used are "mini splits" - each indoor unit has a corresponding outdoor unit. They tend to be the most efficient type (highest CoP).
There are also "multi split" units with a single outdoor unit for several indoor units. The plumbing with those is likely to be a little more complicated, but you have the advantage of just a single outdoor unit. Two of my units have the outdoor unit pretty much directly on the other side of the outer wall that the indoor unit sits on. The third one has the outdoor unit under the extended eaves just round the corner from the back door, with the pipework going up through the eaves into the loft space, and then running about 10m to the front of the house, where the indoor unit is high up on what would have been the external front wall of the house, but which is now inside the "sun room" extension on the front of the house.

If I get a chance I'll try and post some pictures later.