Cylinder suitable for future ASHP

[KOS]

We need to put in a new hot water cylinder in the very near future. After that we’re hoping to go through the process to get a grant and install an A2W heat pump.

 

Ideally we want to choose a cylinder that won’t limit our options. What should we look out for? Any particular brands that are good or bad for compatibility (or any other reason)? Any and all advice would be very much appreciated

[jack]

Welcome to BuildHub.

 

A couple of points (I'm sure there are others):

• ASHPs don't heat water as hot as gas boilers do, so you'll want a larger tank to deliver the same amount of water to things like showers.
• Make sure you get a tank with a heat pump coil, which is longer than a standard coil for use with, e.g., a gas boiler. A longer coil allows for better transfer of heat into the water.

[JohnMo]

Ideally look for a 3m² or larger coil in the cylinder. Telford are reported as good go to Cylinder2Go website. I have a 210L slimline made by Ideal which is good also (3 bed house), lots to choose from. Personally I would avoid pre-plumbed, lots of stuff you don't need. Also don't waste any money getting a cylinder with built-in buffer.

 

You need to do a search on cylinder sizing, it's based on number of bedrooms and it's an MCS guide.

 

The heat pump installers will look for 28mm feed pipe to the cylinder coil. But they will do away with the S or Y plan heating system also, replaced with a 3 port diverter valve.

 

But a heat pump cylinder will be great with a boiler and give really quick reheat times.

Edited yesterday at 13:02 by JohnMo

[sharpener]

Gledhill have reportedly had quality probs with leaking fittings and loose/rattly internals.

 

OSO have a good reputation (and make Vaillant cyls under contract). Mine dates from 1995 and has needed only a replacement pressure reduction cartridge since then. The HP installers re-used it, as changing it out was going to involve substantial building work.

 

Ideal are rebadged cyls made by another major mfr (I forget who) but are actually cheaper to buy from Ideal.

 

IIRC the recommended size is 45 l x (# of bedrooms + 1). This is designed to give you 1 shower p/p.  Should be plenty as with an HP you can reheat cheaply several times a day (depending on tariff e.g. 3 x with Octopus Cosy).

[JohnMo]

28 minutes ago, sharpener said:

Ideal are rebadged cyls made by another major mfr

Gledhill - no issues with mine and paid exactly half the price with the Ideal badge on it, from the same plumbing merchant that sells both. May be the difference is mine is a slimline so coil is shaped differently.

[Nickfromwales]

On 07/07/2025 at 12:53, KOS said:

We need to put in a new hot water cylinder in the very near future. After that we’re hoping to go through the process to get a grant and install an A2W heat pump.

 

Ideally we want to choose a cylinder that won’t limit our options. What should we look out for? Any particular brands that are good or bad for compatibility (or any other reason)? Any and all advice would be very much appreciated

Go to Trevor at cylinders2go (Telford) and mention my username and the forum, as he's given favourable rates to many other members here over the years  

[KOS]

@jack @JohnMo @sharpener

 

Thanks all for your help, we really appreciate it.

So, apart from size, brand reputation, energy rating and coil size are they all basically the same as each other? No ‘smart’ features or bells and whistles or connections or anything that we need to look out for? Just get the cheapest that ticks the boxes and it should work with whatever ASHP you end up choosing?

 

Thanks @Nickfromwales I'll get in touch with him

 

[Nickfromwales]

1 hour ago, KOS said:

@jack @JohnMo @sharpener

 

Thanks all for your help, we really appreciate it.

So, apart from size, brand reputation, energy rating and coil size are they all basically the same as each other? No ‘smart’ features or bells and whistles or connections or anything that we need to look out for? Just get the cheapest that ticks the boxes and it should work with whatever ASHP you end up choosing?

 

Thanks @Nickfromwales I'll get in touch with him

 

Just needs to be a stainless cylinder afaic, as this will outlive both of us, whereas copper will not. 100% avoid glass-lined cylinders (you can tell when it's one, as these have electrically powered sacrificial anodes). These often rot from the inside out, and are utter crap.

[Dillsue]

1 hour ago, KOS said:

So, apart from size, brand reputation, energy rating and coil size are they all basically the same as each other? No ‘smart’ features or bells and whistles or connections or anything that we need to look out for? Just get the cheapest that ticks the boxes and it should work with whatever ASHP you end up choosing?

 

If you're only going to heat DHW with a HP then you'll likely only need a pocket for a temperature probe. If you've got or might get solar PV then a second immersion lower down the cylinder allows you to divert excess solar into the cylinder when the solar is intermittent