A2W for HW only - already have A2A heating/cooling

Martyn1981

SarahEmmm_2 said:

Wow - a remarkable range of prices for what seem very similar systems! Thank you, Qriz, tacpot. Fun fact: I had one of the very first gas combis from Vaillant, installed in 1984. It was great and worked perfectly, though I have heard that Vaillant have had their problems more recently.

matelodave, I did do a Greenmatch form and got referrals from 2 national and 1 local business (who wants to sell me the Energie system). I will prefer a local supplier/installer to hopefully get better aftercare. 

NedS, do you think your friends would be prepared to discuss their Sunamp install? I would be very interested in talking to them.

Hi Sarah, I've literally just done this, after about a year of pondering.

My plan was to go the HPHW tank route, and was looking at the Tesy products that QrizB linked too. Originally, that's because my plan was to provide most heat from my 2 A2A units, then use the HPHW tank with heat exchanger, to heat the upstairs rads. But I actually found that so little top up was needed I could just switch on an oil rad if needed, or dial up the temp (on the A2A units) a bit downstairs.

So, I dropped the heat exchanger part, and was looking for installers for the basic 200lt model at ~£999. That also meant that rads can be ripped out.

But then plans changed again. I noticed that with a new shower head our gas consumption went down even more, from ~90kWh per month, to about 65kWh pm. Only wifey and I, and we take very quick showers. 65kWh included a gas oven, so assuming the 26yr old combi is about 50% efficient when operating from cold, I realised that our leccy savings from a HP v's resistive leccy heating would never pay back. Not knocking the HP idea, I think they are great, but having more tech that may fail didn't make sense in our case.

'Simple' stainless steel HW tank went in 3 weeks ago, into cupboard where combi boiler was. Leccy oven went in a week later, and appointment for gas supply to be capped and meter removed for early November. 

Can you guess at your DHW needs, perhaps the current gas consumption? I'd suggest, that the Tesy (which is pretty cheap), probably makes sense if you use about 1,500kWh+ of DHW per year. That's based on 7p cheap rate leccy. Total man maths, don't take it too seriously, but I'm thinking 1,500 x 7p £105pa, v's £35pa, assuming a COP of 3, or maybe £70pa at a COP of 2, since you are heating the water to a higher temp and at night, But I'm really really guessing.*

The more expensive HPHW tanks, and that's most of them, may sadly not make much sense unless you use large amounts of DHW.

Another concern, is that the HPHW tank fan will make noise when operating. It may be 50db, so possibly a problem if in a room/bedroom that's occupied.

*Edit - Sorry, I immeditaely went into 7p cheap rate waffle. If the leccy price is higher, then the relative savings from a HPHW will be more, so some number crunching is needed. M.