Cylinder Choice, Heat Pump, Gas and Oil Boiler

[JohnMo]

Thought I would drop some information in to a stand-alone topic, about unvented cylinder (UVC) choice, be it for a heat pump or fossil fuel boiler.

 

The normal advice from a plumber is to use gas/oil boiler specific UVC, when installing a fossil fuel boiler and a heat pump specific one for a heat pump.  The primary difference is coil surface area, used to heat cylinder.

 

However I would advise anyone to install only a heat pump specific cylinder, with any heat source.  You generally get a huge 3m²  heating coil, which allows the cylinder to be hot without excessive boiler flow temperatures.

 

This was mine this morning - running in hybrid mode (gas boiler and ASHP)

 

Cylinder temp at 53 Deg, but more importantly the boiler flow temp was only 56 degs.  This ensure good condensation while boiler is running for improved efficiency.  Also if you are using S or Y plan heating schemes it allow a good reduction in flow for both central heating and you can have a hot cylinder.

 

[ProDave]

If you cylinder is large enough you can improve on that by reducing your target temperature, ours is set to 48 degrees which is plenty.  ASHP flow temperature set to 55 degrees max,

[JohnMo]

14 minutes ago, ProDave said:

If you cylinder is large enough you can improve on that by reducing your target temperature, ours is set to 48 degrees which is plenty.  ASHP flow temperature set to 55 degrees max,

Very true, ours is set a little high. Driven by wife's expectations of very hot water in the kitchen sink 

[saveasteading]

1 hour ago, JohnMo said:

Driven by wife's expectations 

I didn't know that energy source could be harnessed.

[JohnMo]

35 minutes ago, saveasteading said:

I didn't know that energy source could be harnessed.

She busy peddling away.

[Nickfromwales]

2 hours ago, ProDave said:

If you cylinder is large enough you can improve on that by reducing your target temperature, ours is set to 48 degrees which is plenty.  ASHP flow temperature set to 55 degrees max,

Wasn’t that after your family beat you up for trying it at 42°? 😜🤣

[G and J]

2 hours ago, JohnMo said:

Very true, ours is set a little high. Driven by wife's expectations of very hot water in the kitchen sink 

My plan is to top up my washing up water with a qooker tap.  I like scalding hot washing up water but want to run my system only as warm as needed for J’s hot showers and my lobster baths.  
 

I can’t work out if I need more than 200 litres….

[JohnMo]

1 hour ago, G and J said:

can’t work out if I need more than 200 litres

We (2 off us) have 210L, 50% of the time it's heated once the other 50% twice a day.

 

But currently, although heated this morning its been further heated to 68 degs via immersion (excess solar).

[Nickfromwales]

1 hour ago, G and J said:

I can’t work out if I need more than 200 litres….

I’d go 250L and time when to heat it, so you’re always using off peak power > ASHP. 
 

Bigger the cylinder, the lower the stored temp. 

 

Any solar planned? Battery?