[Possum]

Having just moved into a very old building we know that we are going to have to replace the elderly boiler and even older oil tank, sooner rather than later. We have been investigating Air source heat pumps but have received quite a lot of conflicting information. Does anyone have any experience of them? If so, which variety have you used?

There is no gas supply here and we have concrete floors so ground source heat pumps are impractical. We have good insulation, draftproofing and double glazing.

[doganjo]

I've only heard of it being used in modern buildings where the insulation is at least of modern Building Standard levels.  However, if your insulation is really good I can see that it shoudl work in old buildings too.  Is it not very expensive though to install in an already built building?  My friend's equipment was partially installed as the building was going up.

[goosepimple]

Hi Possum, my OH and myself are architects and researched this one thoroughly quite recently for our old house - they can be noisy, don't look nice attached to outside of your house, expensive so you really need to stay put, none of which suited us.  We looked at ground source and at a new type of solar panels which do your heating (unusual) as well as your hot water.  All needed extensive works done or a house extension to cope with the apparatus required.  In the end we installed 50mm insulated plasterboard internally on all our external walls and ceilings - made the rooms a wee bit smaller but I can't say I've noticed.  Insulation is definitely the key in old buildings and can make a huge difference - you just don't want to lose the heat you generate, you wan't to keep it in the building - no point in heating it all the time and losing the heat.  Insulate everywhere you can (loft, coombed walls etc).  Put up heavy lined curtains and joiners will put good quality sealants around doors and windows.  We also looked at retro-fitting back boilers to our wood burning stoves, but the amount of money all these things cost in installation doesn't warrant doing it in the first place - hot water for a family of 4 only costs about £250 a year, not loads.  Re-insulating your walls may sound drastic but it costs a lot less.  Stay cosy and have a holiday on the money you might have spent.  All the new gadgetry out there really needs to be designed in to a new build, not retro fitted to an old house.

[FiB]

Echo what Goospimple says... we had a consultant from CAT do us a survey and ground/air source were the least suitable options for our old converted cowshed (V thick stone walls and good, but not modern/passive standard, insualtion).  In addition he said you have to be very careful if you go ahead as some use really nasty coolants (a nasty carbon footprint in whole life terms) and have lower efficiency co-efficients than you might expecting - only sustainable if you are generating lots of electricity.  They can be a dodgy choice.  Our recommended spend priority (in terms of value/return) was insulation (including improving the standard double glazing that we currently have) and wood fired boiler. It cost us £5k to have 2 new woodburners intalled, one with back boiler and plumbed to run HW and central heating.  He also recommended solar thermal and PV for us, but we dont have the capital at the mo. If you were buying in all your wood, I'm not sure the latter would make sense financially.

Look forward to hearing about your decisions and experiences, good luck Fi

[Womble]

Whereabouts are you Possum?   

Air (as a heat source) gets much colder during the winter than the earth (ground source heat pump), so you need to be careful of the specified operating envelope of your proposed system. If your air gets very cold, this will affect the efficiency you achieve, and might also find the unit keeps having to stop to defrost itself.

[Possum]

Gosh. Thanks everyone, for such good replies. I am beginning to have my doubts now, particularly since we are also in a converted cowshed.

On the plus side, we have solar panels and so are generating a lot of our own electricity. We live in Somerset, which is milder than Scotland but still gets cold in the winter. We are currently looking at ASHPs that work in sub-zero temps. They have been used in Germany for many years so I think this problem may have been overcome.

One of our reasons for looking at heatpumps is that it would be nice not to be dependent on oil. Apart from tanker driver strikes, the price just keeps going up so it would be good to find an alternative.

[chrismahon]

They work well in Finland. Although colder the air is dry so they are not repeatedly de-icing themselves. When they do that they take heat back out of the house to melt the ice then restart and they can do it up to three times an hour. You also get a huge frozen puddle underneath so can't site them near a footpath.

The CoP is only about 2 -2 1/2 so payback time is questionable. Agree that insulation is the key and when that's in place you may be OK with just a wood burner and solar panels for water.

[YorkshireLass]

I had the impression that you had to have a pretty well sealed (airtight) building for the air and heat exchange to work?

Or am I thinking of a different system?

[chrismahon]

There are two types of Air source heat pumps YorshireLass. Air to Water, which is used for underfloor heating and Air to Air which is basically a fan heater costing half as much to run.

[Plantoid]

I have come across an air source heat pump that was situated some 20 mtrs away fromthe house and the hot air was brought in in well insulated pipes that ran in a 600 x 600 mm channel under the garden path . This was then piped to the joint outside wall of the lounge and kitchen part distributed at floor level and across the patio doors , behind kitchen cabinets into th hall way and into the dining room , up to the roof void and into the bed rooms & bath room voa boxed on ducts in builting ward robes or the airing cupboard .
 
 The people said they had oil heating as back up but had never had cause to use it .
 This was in the rather cool winter of 1982 ( ? )  when we had minus 18 0c for several weeks and a few days of minus 21 oC out in the open Fenlands

[goosepimple]

Would imagine it was in a new house insulated to a decent standard? or at least a house with good insulation in it (if the house was old).

[Womble]

I had the impression that you had to have a pretty well sealed (airtight) building for the air and heat exchange to work?

Or am I thinking of a different system?

Think of your house as a leaky bucket. The bigger your leaks of heat are, the more heat you have to pump in to keep the level (temperature) up.
 
The problem with heat pumps is that the radiators etc run at a much lower temperature than conventional oil fired systems. This means that you need much more heat transfer area in order to provide the same amount of heating power (this is why they're really good with underfloor systems - far more heat transfer area available than with radiators). 
 
So, if your house isn't well enough insulated or sealed, you end up with a big heat pump system, large numbers of radiators, and high running costs etc in order to keep warm. You can't have something for nothing I guess, and a heat pump is really just an inside-out fridge at the end of the day! 

[chrismahon]

The higher the output temperature the lower the efficiency of the unit so heating radiators and hot water is the last thing you want to be doing, no matter what the saleman says. I know a couple who had a ground source heat pump running radiators and calculated at the end of the year it cost more 'all in' than the old oil system. Air source pumps may be cheaper but they have a much lower efficiency than ground source.
 

[blakeecotec]

I am a renewable heating installer based in Somerset. For new builds I can easily design in a air source heat pump which is a great solution, but for old small to medium sized properties with an existing radiator system. I fit automatic wood pellet boilers. It is normally a simple process to remove oil boiler and tank, connect in the wood pellet boiler to the existing wet system and off you go.  The modern wood pellet boilers and stoves, I fit can be up to 97% efficient, they automatically light and go out, they modulate the power output to match the heating load like modern gas boilers and can be used on sealed systems.  I even fit a condensing self cleaning wood pellet boiler that will burn 3 tonnes of wood pellets betwen emptying the ash box.  Unlike most heat pumps they can heat radiators to 75 degrees, so no changes to your existing radiators and hot water system..   

I do an automatic wood pellet boiler 22kW fitted from £5000 inc VAT, plus you get £950 RHHP grant back.  So more from oil to pellets from around £4000.   
   
I don't bother with wood burners with back boilers unless I am forced to fit them.  They have no government grants, are quite inefficient and good dry wood is hard to come by these days..  Wood stoves with back boilers need regular refuelling / cleaning and require a lot of plumbing changes to change from a oil/gas boiler.  It is for instance very expensive to couple a wood boiler to an unvented cylinder.

I would also recommend log gasification boilers, but you need lots of space to fit them as they need a large 1000litre++ buffer tank and access to lots of dry wood.  I fit these mostly on Farms.

For large heat requirements, > 100kW,  I would consider a wood chip boiler, but you need to put more effort in to realise savings, however, if you have a good local wood chips supplier it could be worth it.   

 I also recommend fitting solar flat panels along with the biomass boiler.  Flat panels look better than tubes, are less fragile and much cheaper.  In the winter they are not so good as vacuum tube solar, but they make it up in the summer when you really need it .   
 
   

[Possum]

I seem to remember that there are quite a few TASers with backboilers on their woodburning stoves and that they usually report high levels of satisfaction. Comments anyone??