Ashp for underfloor heating

jblakes

Evening all, 

We have solid fuel CH which heatsvthe house nicely, what I was thinking of either having gas CH or ashp for underfloor and maybe heat water mainly over summer when cool. Is this possible? Then when it gets very cold then light the burner and heat house, but use ashp to keep temp 18-20 when required?

Kind regards
James

Reed_Richards

I understand what you are seeking is something to supplement your solid fuel central heating, when it's not very cold outside but some heating is desired inside.  Central Heating implies to me that you already have radiators; is this correct?  If so, one option worth considering is a thermal store, a big tank of water that you can heat by various means and use to heat your Domestic Hot Water and your radiators.  The point of the thermal store is that you can integrate or alternate between different heat sources.

Another option worth considering is an air-to-air heat pump, which is basically an air conditioning unit that can be run to heat as well as cool the air.  Because you only require an air temperature of 18 to 20 C this could be run more efficiently that an air-to-water heat pump.  But it doesn't give you hot water.

I think I and others could give you a better answer if you explained in more detail what you have at the moment (and how much you are looking to spend).

jblakes

Thank you for getting back to me.

Yes we currently have solid fuel CH and rads in all rooms linked to it. We were contemplating switching to gas CH so we can essentially turn it on, we have an 18month old and another on the way, so don't really want to be lighting a fire when abit cooler.

So my thought (not sure if possible) was to look at basically another independent heating system as in Ashp/gas for underfloor heating, so wouldn't link to the solid fuel, so we could use it to obviously heat the room via the underfloor when needed. We also have electric emersion heater to heat water at min, when fire not going, which I can only assume to an expensive way to do it. I haven't quite figured out how to overcome that but though.

Kind regards
James

Reed_Richards

At the moment gas is the cheapest fuel available.  The initial cost of an ASHP is very high although you may be able get a lot of it back over seven years from a grant called the Renewable Heat Incentive.  But at current prices for gas and electricity an ASHP cannot compete with a gas boiler on running cost.

jblakes

Thank you for getting back to me. Can you have a solid fuel /gas CH system running together?

Don't want to get rid of the log burner, although could just be used as a log burner.

Kind regards
James

Reed_Richards

jblakes said:

Can you have a solid fuel /gas CH system running together?

I think it would be hard to find an installer that would commit to making such a system work if the central heating water is heated directly by either the log burner or the gas boiler.  The "standard" way to do it would be to heat the water indirectly using a "Thermal Store".

jblakes

OK, are they anygood? A thermal store I mean. 

Although it's looking like we need to switch to gas CH. 

Regards 
James

Reed_Richards

I have never owned a Thermal Store so I don't know how well they work in practice.  I considered one when refurbishing my house but decided it was an unnecessary complication as I did not have multiple heat sources.  This site (which is trying to sell you one) gives an explanation of how they work: https://www.modernstoves.co.uk/product/thermal-store-and-plumbing/300-litre-copper-thermal-store-with-built-in-header-tank/  

Cardew

jblakes said:

Thank you for getting back to me. Can you have a solid fuel /gas CH system running together?

Don't want to get rid of the log burner, although could just be used as a log burner.

Kind regards
James

There have been a number of threads on this subject. This is one post of mine.

Yes there are ways to incorporate solid fuel heating into an gas CH system.

However you need something like a Dunsley Neutralizer to overcome the problems.

http://www.dunsleyheat.co.uk/neutralizer.html

Ensure that you get a plumber with the knowledge to incorporate both systems. Unless it is done correctly you can have serious safety problems.

The difficulty is that without the Dunsley neutralizer the solid fuel burner will be fed with hot water from the gas boiler, even when not lit. It would of course be easy to fit a valve to stop hot water getting to the boiler. HOWEVER if someone inadvertently lit the solid fuel boiler, with that valve closed, the water would boil and water boiling in a closed loop = explosion; and whoever fitted such a valve could end up in prison!

I had such a system with a Baxi open fire and Gas CH, albeit without a Dunsley. It was more trouble than it was worth so I had it disconnected, drained the jacket of the Baxi and use it as a simple open fire.

Whilst the large thermal store feeding radiators suggested above would work; the difficulty would be at the times you want the occasional quick burst of CH - say 30 mins on a September evening. You would need wait to have a large tank of water heat up.

Reed_Richards

Cardew said:

Whilst the large thermal store feeding radiators suggested above would work; the difficulty would be at the times you want the occasional quick burst of CH - say 30 mins on a September evening. You would need wait to have a large tank of water heat up.

Well no because the tank would be permanently hot to provide hot water to the taps.  Your hot water supply is achieved by passing cold water through a coil in the thermal store.  That way you get mains pressure hot water without the faff of having a pressurised tank.