If you look, I have a spare 2 ports on the left hand side of the buffer. One is about 2/3 of the way up. Would this be a better option? Or does it have to go to the top nozzle?

I have 2 circuits, both open loop. One is supplying approx 120m2 of UFH circuits and the other is supplying upstairs (2 floors) of rads? You think the pump would struggle supplying enough flow?

Thanks again

 So keeping both the emitter return and the heat pump return on the lower ports can be acceptable, provided the flow path through the vessel is continuous and you’re not inadvertently short-circuiting the top section.

Without doing some horrendous modelling, or fabricating some transparent tanks, I would think that there is quite a significant risk that the upper section is effectively short circuited if both connections are at the bottom, particularly if the erstwhile buffer tank was designed to encourage stratification.

There will be some turbulence of course, and a bit of a convection current (hopefully not much if the tank is well insulated) but not a lot really to stir it up.  So personally I would go in at the top and out at the bottom even if it makes the plumbing more difficult.

On your question about port orientation, in a true volumiser configuration (not decoupled) you’re not trying to achieve stratification in the same way as a buffer. So keeping both the emitter return and the heat pump return on the lower ports can be acceptable, provided the flow path through the vessel is continuous and you’re not inadvertently short-circuiting the top section.

In practice, like @judith alluded to, this is the more conventional way of plumbing in a volumiser.

On the pump question, a 7 kW Vaillant’s internal pump is generally capable of handling a typical single open circuit system provided the hydraulic resistance is reasonable. The fact that it’s currently circulating 1200 litres (I assume you mean system volume, not flow rate) is less relevant than the required flow rate and head. What's important here is whether, once you remove the secondary pump and decoupling effect of the buffer, the internal pump can achieve the required design flow at the actual system resistance. If it can't, you'll drown in flow errors.

Have you calculated your total system volume? Having an effectively smaller volumiser may not matter.

I want to keep the return from the UFH/rads and return back to the heat pump, on the bottom ports of the new "volumiser"

If you do that then most of the water in the top of volumiser will be "out of circuit" and not adding to the heated volume?  I recently had a buffer converted and it was piped in at the top and out at the bottom (on the flow side FWIW).

First post here.

I have a 7kw Vaillant with a 100l 4 port buffer. I'm looking to squeeze every bit of efficiency out of the system and so I'm looking to re-pipe my buffer to a volumiser on the return side. I have attached an image to show my proposed re-piping but wanted to check if all looks OK. Basically I want to fit a bypass in around the buffer and secondary circulation pump so if, for any reason, I wanted to revert back to the original set up, I can.

My main questions are:

1. For ease and minimum work I want to keep the return from the UFH/rads and return back to the heat pump, on the bottom ports of the new "volumiser". Will this be OK or will I need to cross flow the volumiser? In at the top, out of the bottom or vice versa?
2. Will the internal pump on the Vaillant cope as the only pump on the circuit? Currently pumping 1200l quite happily.

Thanks all

What’s particularly telling is that these quotes are usually from installers I’ve never come across before, and they all follow the same pattern. Very stock, boilerplate proposals that suggest little real thought has gone into the actual design of the system. A buffer tank by default, multiple circulation pumps, zoning, on/off stats and often a fixed flow temperature thrown in for good measure.

Because of that, I’ve put together a video that goes into why buffer tanks can introduce efficiency losses, how mixing (distortion) and separation can affect radiator performance and why homeowners often end up paying for design shortcuts every time the system runs.

This isn’t about saying buffer tanks are always wrong (they absolutely have valid use cases) but in typical UK homes they’re still being used far more often than they should be and almost always for the wrong reasons.

If you’re currently looking at quotes, or you’ve already got a system with a buffer and are wondering whether it’s helping or hindering performance, this should give you some useful context.

Here’s the video: https://youtu.be/QLKlSH3rIOA

As always, interested to hear others’ experiences, especially from homeowners who’ve removed or repurposed a buffer and seen what difference it made.

Now, I think I have been moderately successful in achieving temperature differences between flow into and then out of the LLH to the secondary pump and then between the return flow from the emitters to the LLH and hence on to the return to the primary pipe return. Most of the time, the differential is within ~0.2 degrees either side of the LLH - so the losses are fairly low.

Come mid October, I noticed that the flow rate (dictated by the Daikin unit itself) had taken on a third level; usually the flow would step between ~28 lpm and then reduce to ~ 14 lpm. As the lower rate was the dominant, I had set the secondary pump (Wilo Pico) to match with the ~0.2 degrees difference across the LLH. From this time, the flow rate took on a dominant rate of ~7 lpm and I tweaked the secondary pump to match.

I still see the flow rate start a cycle at ~28 lpm then drop and then drop again. I am curious to know if any reader has seen similar activity and if so why this might be please? I also wonder about the efficiency at the higher flow rates as presumably LLH distortion may increase? I think the lowest flow rate still has the longest running time so suspect I should be satisfied with my present setting - but I would be grateful for any observations please. I have attached a plot of the flow and temperatures seen in the last few days.

Regards, Toodles.

'We fit systems with buffers or a low loss header, never without either.

@mars That response surely deserves a nomination for Turkey of The Year, for the company itself not for the specific installation.  It shows a company which either consistently does the wrong thing, or lies to its customers.  Either way it doesn't deserve to be in business unless it changes radically.

Here’s what they wrote:

“I’ve been watching your videos on YouTube, I have learnt so much!

We are moving house in the next couple of months and have an ideal opportunity to install a new heating system from scratch.

I have had a site visit and quote from an installer but they are telling me I will need a buffer in the system. When questioned why they replied:

'Your research seems very very high! We fit systems with buffers or a low loss header, never without either. The reason is because to keep a heat pump running efficiently, we need a higher flow rate than most heating systems require, so the heat pump satisfies the buffer and the buffer satisfies the space heating system. This stops the heat pump short cycling, short cycling is bad for efficiency and the life expectancy of the heat pump compressor will be compromised.'"

This kind of explanation should set off alarm bells for consumers everywhere. If the default answer from an installer is “we never fit a system without a buffer or LLH,” it usually means they’re designing to their own convenience (or they're just incompetent) rather than what’s best for the homeowner.

It’s fantastic to see homeowners pushing back and questioning these decisions!