I am seeking personal experiences of Air to Water heat pumps.
12 years ago I fully renovated our current home and installed a domestic hot water/wet central heating system which is powered by an extemely efficient wood burning fire with wrap around hot water jacket. This system has the benefit of having a log fire behind glass that looks good too. The system continues to work as good as the day it was installed but that cannot be said for the systems operator who is now 12 years older!!
Each year we purchase 16 cubic metres of mature seasoned oak and this provides all the hot water and heat we need throughout the colder months. When the fire isn’t in use then the system automatically switches to heating domestic hot water by electricity.
The wood burner sits on an internal gable wall with the flow and return pipes leading to the internal corner of the lounge where the pump and all other gubbins are situated.
My thoughts are that in simple terms the flow and return pipes can be diverted through the gable wall and connected to an air to water heat pump which will provide all the hot water and central heating we require while a replacement log burner without a water jacket will provide a heat boost to the lounge and also look good ( I presume if a wood burner has a water jacket then it cannot be safely used if not connected to a heating system?)
The benefits I can think of are:-
less oak to purchase which I have to stack, cut and feed the fire continually in the cooler months.
We will have heat first thing in the morning without the need to light the woodburner.
When we go out for the day, or longer, the house will not be cold when we return which is the case now.
much less work for old bones!
My concern is the efficiency of an air to water heat pump.
I read that they are less efficeint in colder weather which is exactly when we would need it to perform well.
Any personal experience of my proposal or suggestion of a variation would be greatly apprieciated.
I would have thought that if the water jacket was drained and the pipe ends left open, it wouldn’t make any difference if it was left in place on the fire, I suppose it depends on what type of material the stove is made of.
Yes it has 2 coils but don’t really want to mess around with the current set up. Is your thinking to leave on coil connected to the fire so that in case the air to water jobbie fails we would still have hot water?
Currently when we dont have a fire lit the cylinder is automatically heating by electricity and I am presuming that would still be the case.
If your house is well insulated it will work. If your house is well insulated and has underfloor heating or big rads it will work very well.
The drawback to most is the heat output to rads is lower - so heating is more low and slow. If your house leaks the slow approach doesn’t work. You can get higher output systems but they’re noticeably more cash.
The tech speak is beyond me, but all I can add is that we have an air to water system that we like. As said above we have underfloor heating downstairs and it gives a nice gentle heat. Upstairs large rads.
There is a small woodstove as a top-up but mainly for ambiance.
In very cold weather it is no more efficient than electric heating, but generally seems cost-effective.
No good if you want rapid increases in heat. And the pump itself has to stay frost free which is a pain if you want to go away in winter as can’t drain the system down so have to leave some heat going through it
What is the rating of the heat output of your wood burner?
Yes you can as others have said continue to use it with an empty and open water jacket boiler, they just take up more space but you are used to that already.
Using the heat pump to at least pre heat the water in the tank will save money and electricity. Depending on the unit, some produce sufficient temp to tick the legionella box.
Its not necessary to drain down if you are away, you can fit a trace heating tape, they are low power, self regulating heating tapes used on condensing boilers waste pipes and often on farm water pipes.
This is our woodburner, 10kw to the room it stands in and 16kw to water heating/central heating.
We dont have underfloor heating but the floor construction incorporates a 100 insulaton beneath the concrete so no loss of heat through the floor up or down.
The house is over insulated, if that were possible, and fully double glazed. Basically it is a new house inside its 200 year old shell.
As a principal residence it is always occupied in the winter, as too cold to go travelling, so no need to drain anything down.
My main concern as @JaneJones has mentioned is how slow the system might heat up with air to water unit suggesting it would provide heat similar to an electric installation. We had electric storage heaters in a previous house which were less than rubbish so if an electric radiator system is no better perhaps I would not be happy with air to water sourced heating?
The current system dedicates the generation of hot water to the 400 litre hot water storage tank before then sending hot water to the radiators. The hot water tank is super efficient keeping the water hot for 3/4 days with very little heat loss if electricity is not reheating it.
One of my principal concerns is how long an air to water unit would take to heat the domestic water before the system switched to providing water to the rads.
As for the existing woodburner sounds like we wouldn’t have to replace it which is good news. I will give the tech department at Broseley a call to verify that with this specific unit.
I have an air to water heat pump which heats radiators in about half my house (200m2, and these radiators were there when I bought it) and the floor in the other half. There’s a dual circuit which comes out sending water round at different temperatures. I vastly prefer the heated floor which I put in 20 years ago when I converted those buildings.
If you are there all the time that shouldn’t be an issue? It’s only when it is unoccupied we have turned the system down to hors gel, and then have a cold house. But the wood stove is placed centrally to heat the place quickly while waiting for the heat pump to do its thing.
We had one fitted last year to replace our fuel oil burner for central heating and hot water production.
Things to consider:
The temperature at which you want your outlet water heated to as it enters the radiators - steel radiators require higher temperatures than underfloor heating pipes in order to feel warm, which in turn will impact on your choice of heat exchanger power - we went for one that was capable of producing outlet temperatures commensurate with the steel radiators we had. Although this cost more, as we had a 15kw system installed instead of a 7-9 kw system, we never had a problem with heat provision over the winter, and we live at 600m asl, in the Auvergne, and are exposed to the north wind.
Our average electricity bill was 700 EUR/yr prior to the installation of the heat pump. We have just had our bill for this year, and it has come to 1628 EUR, including the 48 EUR fee for switching power to the house 12KWH (something else that needs to be taken into account in case you buy a higher powered heat pump exchange system) as most domestic EDF contracts are often only 6 or 7KWH.
Prior to installation of the heat pump, the fuel oil bills per annum were on average 2500 EUR (and climbing). We also had an “insert” closed, log burning fire, which we used in between the main changes in season to avoid putting on the CHS. We never had to buy wood as we have plenty on the property, and I’ve always cut and split our own. Absent the installation costs, which were significant, even with a grant, in the first year of use, we have saved nearly 37% on our usual expenditure on fuel oil, and that includes the whole winter period (on average the CHS is on for nearly 6 months due to the amplitudes of temperature). Obviously, if one takes into account the investment costs, then we don’t yet have a ROI, but if we end up saving even just 20%/yr on energy costs over fuel oil, I consider that as a massive win.
To add to what I have just commented, our system heats up the water in the integrated hot water tank before distributing to the radiators - it takes about 30 min for this to happen, but the program controller takes care of it all.
We have thought long and hard about converting over, but going solely over to using the wood burner/hot air system has more than halved our heating bill from the gas costs of the central heating down to around €600 a year.
While I am able to wheel a wheelbarrow over once a day filled with logs I cannot justify the outlay and we like the woodburner look as well.
Many thanks to all who have given their experiences to my question. I am still undecided but much better informed. Next step is to get some quotes which will certainly focus my thoughts when balancing cost to convenience.
Thats the bit I am concerned over, Passiv haus set a standard of insulation that requires minimal heating. If you are over insulated you would be above Passiv haus standard, even if you equal it, the 16 cubes of wood required over autumn winter would suggest you are still not that well insulated, although you maybe much better than most. What is the flow temperature of your central heating? Air source to be more efficient require a flow temperature of 40-45c hence why larger radiators are needed and/or the system operated for longer. How slow the system may heat up depends not just on the flow temerature but on building losses. For sure the 16kw log burner at 300c is going to kick out a huge amount of noticable high temperature energry so sellers/designers would have to take that carefully into consideration.
Noted. We have purchased 16 metres each year for the last 11 years. Burning used to start end of September to early October through to May time with a build up to full burn 7 days a week during mid winter. The last 2 winters have been shorter and this year still no fire yet. We have had a 2/3 metre surplus of firewood the last 2 years, I know, global warming!
As for the insulation, yes perhaps much better than most and an old structure has its limitations however when are heating system was installed we had radiators on both the ground and first floor and to this day we haven’t had the first floor rads on and we have open stairs from the lounge.
I have been a builder some 50 years and experienced the development of insulation requirements over that period from effectively none to what we have today. I renovated our current home 11 years ago and believe me when I say the insulation regime I used then is still way ahead of what many adopt now.
As for technical flow rates and such I will have to look into that and report back.
Adding to my forward thinking, I shall be continuing this winter as I have for the last 11 years as any supplier/ installer worth considering will already be booked up this year so my thinking is for next winter 2024/25.
Hi @vero , can I ask what make and model of air-water heat pump you have ? I will be looking for one in the next couple of years to replace the now 11 year old ground-water heat pump we have as an air-water would be less than half the price of replacing the ground-water one.
