Extending a property with an ASHP and underfloor heating

jackieblack

Hoping for some advice from those more knowledgeable, please 

Have viewed a property we really like this morning which was built about 3 years ago with an ASHP and underfloor heating, neither of which I know anything about.  We would need to build on, either a ‘proper’ extension and/or a conservatory/sun room (with a proper roof, not glass), and I’m wondering whether this would be possible and how it would work. (The alternative would be a small independent grannie annexe). Are heat pumps generally only sized for the original property? The home hasn’t been lived in, so I’m assuming the heating hasn’t been running or serviced since it was installed. 

Is this likely to be a problem? (eg do these things seize up if not run regularly?)
What should we be looking for/checking, please?

Ready and willing to learn (although not technically minded) 
Thank you

QrizB

Just going by traffic in this forum, the usual situation seems to be that the heat pump is too big and has to cycle inefficiently. So you might find that there's spare capacity for a modest extension.

How big is the property now? How large an extension? How powerful is the existing heat pump?

jackieblack

Thanks 
Currently 100 sq m, according to the EPC.
Extension size, maybe about 11-12 sq m (ish)?
No idea how powerful the existing system is (how would I find out? Estate agent didn’t appear to know much about it (other than personal experience of having similar in own home)

QrizB

So adding 10-12% to the floor area? That's likely to be within the capacity of the current heat pump (worst case you'll need to run the backup heater during really cold weather).

It's a shame you didn't get the make and model of the heat pump when you viewed. Maybe ask the EA if they have that info, or can get it?

jackieblack

We’re going back for a second viewing on Tuesday, I’ll see if I can get it then. Where should I be looking, please? On the unit outside? Somewhere amongst the collection of gubbins in the cupboard with the (enormous!) water tank? Or somewhere else?

Netexporter

There should be a data plate on the outside unit, that will tell you the model and nominal power.

jackieblack

Thank you 🙂

jackieblack

Is the fact that the system hasn’t been run for the 3 years since being installed likely to be an issue? I know pumps in a ‘normal’ (ie traditional gas boiler) system can jam/seize if not used for a while

QrizB

The plate (probably a silver coloured sticker) will look something like this one (which I downloaded from an eBay listing):

matelodave

You should try a get a look at the MCS Certificate and the Energy Performance Certificate. (EPC)

The EPC should give you a rough idea of the heating energy required  for the place whereas the MCS cert should give you the design requirements and annual heat to be generated by the system. 

If its a new build then it should be well insulated but you might find that the heatpump has been sized to just about manage the heat loss of the building. although you might get away with some supplementary heating when its ever so cold. A properly specified system should actually be running pretty close to its rated output especially with fully underfloor system which generally runs at lower temps than a radiator system. Is it u/f all over or are there rads upstairs as well.

Extending the the system may be relatively easy (or really difficult) depending on how its been installed and where the plumbing is routed between the heatpump  (actually after the diverter valve which diverts water between heating and the hot water tank) and the underfloor manifolds.  That's where you'll probably have to "T" into it to get plumbing to the location of the proposed extension. so you need to try an figure out where the pipe runs will be. Ideally they should be fairly large bore, probably 20-25mm especially if its a long run.

What sort of heating are you contemplating in the extension - underfloor or radiators as that could have a bearing on what is possible.

matelodave

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.