Flow-Through Heater HOTJET FW

Hygienically clean hot water without a boiler. An integrated heat exchanger station controlled directly from the heat pump — for the price of a stainless steel tank.

The heat pump charges a buffer tank with heating water. When you open the tap, cold drinking water flows through the exchanger and is instantly heated to 45–55 °C. No stagnation, no storage of drinking water, no dead legs.

Why not a boiler?

Tank-based DHW heating has a fundamental drawback: water stands still, accumulates sediment and scale, and becomes a breeding ground for bacteria. Flow-through heating solves this in principle — drinking water is only heated at the moment of use as it passes through the exchanger.

Legionella pneumophila — bacteria that thrive in standing water at 25–45 °C. Inhaling contaminated aerosol (e.g. while showering) can cause severe pneumonia. Flow-through heating minimises this risk.

How it works

1. Tank charging — the heat pump heats the water in the buffer tank, ideally during off-peak tariff or from PV surplus
2. Heat battery — the tank stores energy in a closed heating water circuit, no drinking water inside
3. Flow-through heating — when the tap opens, cold water flows through the exchanger and is heated instantly
4. Precise control — electronics modulate the circulation pump and maintain output temperature at 45–55 °C

Connection diagram

Advantages

• Maximum hygiene — no standing drinking water, minimised Legionella risk, turbulent flow prevents scale build-up
• Full heat pump output — charging the buffer tank at full HP output without limitations from a coil exchanger inside the tank
• Higher COP — an oversized exchanger allows lower tank temperatures (45–50 °C), so the heat pump runs more efficiently
• Tank longevity — a neutral buffer tank with no contact with drinking water, no corrosion, no anode maintenance
• Easy capacity expansion — increase system capacity at any time by connecting additional tanks of any volume
• Custom tank and exchanger combination — choose tank volume and exchanger size to match the building’s actual needs
• Electric element charging from PV — the buffer tank can be charged with standard electric heating elements from PV surplus
• Retrofit to existing tanks — easy connection to existing buffer or stratification tanks, no structural work needed
• Unlimited hot water — as long as the tank is charged you have DHW; hot tub + shower simultaneously without loss of comfort
• Control from HP at no extra cost — control is integrated directly in the Hotjet heat pump, no additional expenses
• Neutral tank (chameleon) — the tank switches function as needed: DHW, heating, cooling; PV integration, boiler and passive cooling in one
• Tank chaining — connect additional tanks of any volume to increase capacity, swap the exchanger to increase flow output

What’s in the box

• Stainless steel SWEP heat exchanger (AISI 316L, oversized)
• Circulation pump (electronic, modulated, class A)
• Flow switch (automatic activation on demand)
• Fittings and insulation (complete accessory kit)
• Buffer tank with thermal insulation (200–1,000 l)
• Optional heating element (2–6 kW for reheating / PV charging)

Use cases

Family house with a heat pump — the HP charges the tank mostly during off-peak tariff, COP > 4 thanks to lower charging temperature. Hot tub + shower simultaneously without comfort loss. Typical setup: 300 l tank, 25 l/min flow.

Renovation with an existing tank — the old stratification tank stays, you simply add the Hotjet FW module. No demolition, no new piping — just connect the heating and water circuits. Installation in 1 day.

Commercial building (gym, guesthouse) — the oversized exchanger covers even peak evening demand in larger buildings. In summer, the system can switch to cooling mode. Typical setup: 800 l tank, 50 l/min flow.

PV integration — the neutral tank acts as thermal storage for PV surplus. Smart control automatically uses solar energy. Combined DHW, heating and cooling from a single tank.