Changing from 4-port buffer to volumizer

Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls

Last Post by Andy1618 2 hours ago

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Andy1618

(@andy1618)

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Joined: 2 hours ago

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Topic starter 28/12/2025 10:53 am

Background
I bought a house at the beginning of 2025. There was a gas heater installed, but it was 20 years old, had a lot of switching on and off, and was on its last legs. The house was thermo-modernized in 2019, so I decided to go for a heat pump.
I installed a Midea MHC-V12WD2RN7. According to the heat loss calculations, our house needs a 10 kW unit, but since this Midea is an inverter model, the extra 2 kW shouldn’t hurt. It also has an auxiliary heater, and it uses R290, so it sounded like a good choice.

Installer company
The company I chose seemed very professional. Everyone I was in touch with before the installer showed up was very professional as well.
Unfortunately, the installer did a very poor job, which forced me to learn about heating and heat pumps. Since the installation, there have been five visits to fix things I noticed were done wrong (for example: the tray heater not connected, the 3-way valve connected the wrong way around, and many other issues).
These issues were fixed fairly quickly. The last fix was done by the installer’s manager, so it seems like I’m finally dealing with someone more knowledgeable — but my trust is completely gone.

4-port buffer
Probably no surprise here: I have a 4-port buffer, and I’m seeing a very large temperature drop.
• With 35°C set on the heat pump, I get only ~30–31°C at the pump groups.
• It seems like the flow on the heat pump side is much lower than on the house side.

House heating setup
I have two loops:

Loop 1 (floor heating)
HSM 25/6 BU-EXP (Wilo pump, check valve, ESBE mixing valve)
• Ground floor: floor heating in 9 loops (see image, igonre the arrows, those are showing stuff flow meters)
• Plus: 1 loop for the 1st-floor bathroom floor heating with an RTL valve
• I keep the RTL valve and the ground-floor floor heating fully open

Loop 2 (radiators + convectors)
Buderus HS 25/6 BU (Wilo pump, check valve)
• 3 radiators in the upstairs bedrooms
• 2 convector radiators in the living room (not used at all)

The previous owner was concerned that the floor heating wouldn’t be enough and installed the two convector radiators “just in case.” The floor heating is doing the job, so those convectors have never been used.

Current comfort
Right now, with all loops open (except the convector radiators), I can reach comfortable indoor temperatures. The bedrooms are about 1.5°C cooler than the rooms with floor heating.

The problem / questions
My main concern is the temperature drop and the resulting efficiency loss. I want to request modifying the 4-port buffer to make it a volumizer.
My questions are:
• Should the volumizer be on the flow side?
• Should there be a pressure relief valve as a bypass, just in case?
• Should the circulation pumps on the main loops be removed?
• Should the two main loops be modified into one (I’m never going to use high-temperature heating)?
• Can I keep the two loops but remove the pumps?
o If yes: should I have some way to control how much flow goes to each loop?
• What else should I pay attention to?

Thank you in advance for all the help!