Extending a property with an ASHP and underfloor heating

jackieblack

I've got the EPC - it scores 85, making it a B
It says estimated energy needed is 4064kWh pa for heating, 2228 kWK pa for hot water 🤷🏻‍♀️

I would also plan to install solar pv (with a battery?) 

jackieblack

matelodave said:

If the system hasn't been run for a considerable time then the bare minimum should be a check that its still up too pressure (theres usually a pressure gauge or via a reading on the controller).

Check that it runs and produces hot water and that the diverter operates to swap between hot water and  heating depending on the settings as that's more likely to seize than the circulating pump. Make sure that when calling for heat that the manifold gets warm and when calling for hot water that the tank starts to warm up. Check that any zone valves operate correctly as well.

Generally you'll find that the hot water doesn't get as hot as you maybe used too, possibly only around 50-55 degrees and an underfloor system without rads may not get above around 40 degrees.

TBH I'd request a full service of the heating system (by someone who knows what they are doing) as it will probably be out of warranty. You want to satisfy yourself that its in fine fettle and that all the controls are working properly before you take it on.

Thank you
How much should I expect a service to cost, if vendors won't get it done?

I don't understand what a diverter/zone valve/manifold is...  - is there a 'ASHP/underfloor heating for dummies' type thing you would recommend? (Googling isn't producing much of any help, it's all too technical for me... 😳)

matelodave

The EPC tells you how much energy the place needs, its the MCS cert that tells you whether the system is designed to provide it all, and the unit rating (on the rating plate or the specifications) can tell you how much it can actually provide when it gets everso cold ( in the depths of winter when the sun doesn't shine and solar panels don't do much, if anything)

As suggested above find out the make and model of the heatpump and if possible its rating (although that can be gleaned from the on-line spec if you've got the make and model info.) Builders are notorious in fitting the smallest unit they can get away with and your EPC suggests thats it a very well insulated house so you may only have a 3-5kW unit which could struggle provide enough heat  for an extension.

Although that said, its probably not ever difficult to fit a larger unit but you are unlikely to get the £7.5k grant towards it.

jackieblack

matelodave said:

The EPC tells you how much energy the place needs, its the MCS cert that tells you whether the system is designed to provide it all, and the unit rating (on the rating plate or the specifications) can tell you how much it can actually provide when it gets everso cold ( in the depths of winter when the sun doesn't shine and solar panels don't do much, if anything)

As suggested above find out the make and model of the heatpump and if possible its rating (although that can be gleaned from the on-line spec if you've got the make and model info.) Builders are notorious in fitting the smallest unit they can get away with and your EPC suggests thats it a very well insulated house so you may only have a 3-5kW unit which could struggle provide enough heat  for an extension.

Although that said, its probably not ever difficult to fit a larger unit but you are unlikely to get the £7.5k grant towards it.

Ok, thank you 

jackieblack

Would any decent builder know about heat pumps these days? Or will I need to look for a specialist?
Could the extension have a radiator, instead of underfloor heating? Would that be simpler or more complicated?

QrizB

jackieblack said:

Would any decent builder know about heat pumps these days? Or will I need to look for a specialist?

Any decent builder will either know, or know where to get specialist advice from.

Not all builders are decent.

matelodave

To answer your question I'd recommend a proper, possibly independent, heat pump installer rather than the builder. There are plenty around nowadays and they now know what they are doing whereas I'd be a bit wary of a builder, especially if he's marking his own work.


Underfloor systems tend to work for longer at lower temperatures to achieve even heating and higher efficiency (lower running costs).

Radiators can do the same but tend to be larger than normal because of the lower flow temps so there's no reason why radiators cannot be used proved they are sized properly. There are plenty of heatpump installations around with underfloor heating down stairs and rads upstairs or rads all round.(my system , in a bungalow, has underfloor all over plus a towel rail in the bathroom)

The old days with gas boilers there was plenty of heat available, they ran at 70 degrees or more and heating requirements and radiator sizes were usually guessed using rule of thumb estimates. It didn'nt matter if they were oversized because you could turn it down a bit

Nowadays heat pumps are much more efficient when run at lower temps and sized correctly to match the heat load. MCS require more precise heatloss calculations to ensure that the heatpump and emitters (underfloor or radiators) are correctly sized to match the heat loss of the building so hopefully the system isn't either over or under specified. The lower you can run the flow temps the cheaper they are to run so low temp and larger radiators are used.

They can be incredibly efficient and cost less than gas or oil to run if specified correctly, installed and commissioned properly and, most of all, used correctly.

The can be run virtually for free with enough solar and battery capacity, although you do need to import electricity in the winter as there just isnt enough sun around, and that's when a heatpump works the hardest.

However with an off-peak overnight or special tariff to keep the batteries charged you can minimise the winter cost and offset it by flogging spare leccy back to the grid during the summer. Its may be a bit of a balancing act but there are plenty of forumites who do just that and even make a profit.

FreeBear

matelodave said: Although that said, its probably not ever difficult to fit a larger unit but you are unlikely to get the £7.5k grant towards it.

But as all the hard work has already been done (MCS certification, installation, etc), a simple HP swap shouldn't be hugely expensive. As long as the pipework is big enough, and the supply cable capable of handling the extra power... I'd budget around £5K, which is a trivial expense when compared to the cost of an extension.

shinytop

jackieblack said:

Would any decent builder know about heat pumps these days? Or will I need to look for a specialist?
Could the extension have a radiator, instead of underfloor heating? Would that be simpler or more complicated?

A bit more complicated to mix rads and ufh because they'll need different flow temperatures.  Servicing a 10% extra heat loss by adding rads to an existing ufh system might be problematic and might end up requiring a lot more than 10% extra power.  Much better to extend an existing ufh setup with more ufh.  

The other point to note is that if the installation has been specified to MCS standards, it needs to heat the whole house to MCS standard room temperatures at an external temperature condition exceeded for 99.6% of the year.  It's a bit more complicated in reality but this means the ASHP should very rarely be running at full power for sustained periods.  If you're happy for a slightly cooler house (MCS standards are quite generous) or to use extra heaters when it's really cold then you might be OK even if the ASHP is precisely matched to heat loss.  

Finally, as others have said, find out the make/model.  Some ASHPs can't actually achieve their badged ratings in real (i.e. cold) conditions.                

jackieblack

Second viewing today, here is the plate from the outside unit
We have also discovered that the system has, in fact, been running since installed, set to 15 degrees.