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Unvented Cylinders

Unvented Cylinders

Solfex are proud to offer a complete range of unvented stainless steel cylinders specifically for heat pump applications providing mains pressure domestic hot water. Utilising an already well established stainless steel unvented hot water cylinder, this product has been developed to maximise the lower temperatures available from the heat pump.

The heat exchanger is a totally new design. It consists of a multi-pass corrugated stainless steel tube in parallel to reduce the pressure loss whilst maximising the heat exchange. Many medium to large heat pumps need heat exchangers in the store that will cope with the higher flow rates associated with primary temperatures that are typically 50˚C or 60˚C.

Due to the fact that many heat pumps will not raise the stored water temperature to 60˚C, which is necessary to prevent the growth of legionella, the SOLHP range of cylinders are supplied with an immersion heater and a thermostat.

Duplex Stainless Steel

The latest high specification Duplex stainless steel resists all forms of corrosion including crevice and stress whilst its high mechanical strength gives it durability. The very latest automated welding procedures along with full post weld treatments guarantee welds that are as strong as the metal. All
cylinders are factory pressure tested to a full 12 bar which is four times the normal working pressure.

Corrugated Stainless Steel Coil

SOLHP cylinders use a high heat transfer corrugated tube heat exchanger to give a 20% faster recovery than plain tube. It is also lighter and stronger than plain tube making the vessel the lightest and easiest to handle on site.

Heat Loss

All SOLHP cylinders are manufactured using the very latest HCFC free EnviroFoam insulation. This has an Ozone Depletion Potential (ODP) of zero and an industry leading Global Warming Potential (GWP) of 0.7. Tests show that the 50mm of EnviroFoam insulation injected into the case and covering both domes achieves astonishingly low levels of heat loss, which ensures it is fully compliant with 2010 Part L requirements for both new build and replacement cylinders.

25 Years Guarantee

The 25 year guarantee underlines the confidence the manufacturer has in its own products.


All Cylinders are supplied with
  • Combination inlet group incorporating pressure reducing valve, strainer, check valve, balance cold take off point, expansion relief valve and expansion vessel connection points.
  • Potable expansion vessels c/w flexible hose and wall bracket
  • Tundish
  • Dual control thermostat and combined overheat thermostat (x2)
  • Two port (28mm) zone valve for primary circuit
  • Wiring junction box for primary system
Quality Standard

All SOLHP cylinders are manufactured in accordance with BS EN 12897 the specification for unvented water storage vessels. The cylinders have been tested by NSF-WRc and WRAS, and found to comply with Building Regulations G3 and
Water Regulations.

In performance, it complies with the requirements of BS EN 806-1 to 5 and meets the NHBC criteria for domestic properties. Our manufacturing partner also operates a quality management system audited and accepted by the BSI in accordance with BS EN ISO 9001:2008.

Special features
  • The latest and highest quality Duplex Stainless Steel
  • 25 year guarantee.
  • Fast reheat rate from its purpose designed low resistance coil.
  • One of the highest insulation ratings on offer today.
  • The Stainless Lite HP SOL is supplied with all the necessary connections including two dry thermostat pockets.


Capacity - Total Volume  l 180 210 250 300 400 180 210
Dedicated Solar Volume  l 65 75 90 105 130 - -
Standing Heat Loss Rate  kWh/24h 1.48 1.7 1.85 2.04 2.82 2.01 2.23
Weight (empty)  kg 33 38 43 49 61 33 37
 kg 213 248 293 349 461 213 247
Pressure Regulating Valve Setting  Bar 3 3 3 3 3 3 3
Expansion Relief Valve Setting  Bar 4.75 4.75 4.75 4.75 4.75 4.75 4.75
Temp Setting
(P&T valve)
 °C 95 95 95 95 95 95 95
Pressure Setting (P&T valve)  Bar 6 6 6 6 6 6 6
Expansion Vessel Size (volume)  l 18 24 24 35 2 x 24 18 24
Expansion Vessel initial charge pressure  Bar 3 3 3 3 3 3 3
Height mm 1305 1495 1745 1991 2030 1790 1970
Diameter mm 550 550 550 550 550 550 550
Surface Area of Solar Heating Coil m2  0.68 0.68 0.97 0.97 1.27 - -
Solar Coil pressure loss* Bar 0.191 0.191 0.241 0.241 0.31 - -
Heat Pump Coil Surface Area  m2 1.36 1.56 1.94 2.04 2.91 3.01 3.01
Heat Pump Coil Thermal rating*  kW 24.3 26.2 27.5 34.2 47.2 32.8 31.2
Heat Pump coil pressure loss*  Bar 0.048 0.054 0.06 0.019 0.027 0.018 0.018

* Measured at 151lpm primary flow rate


Model Selection Guide
Number of Bedrooms in Property Model
1 SOLHP180
2 SOLHP210
3 SOLHP250
4 SOLHP300
5 SOLHP400
6 SOLHP400
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