💡 Hot water cylinders work hardest alongside a heat pump — the cylinder stores the heat pump's output for domestic hot water, cutting fossil fuel use to near zero. SEAI grants of up to €1,600 available for hot water cylinders. Apply at seai.ie →
OSO · Heat Pump Indirect · Ireland 2026
OSO Optima XL HP 200L — Ireland 2026
Norwegian-engineered heat pump cylinder — factory-recommended by Mitsubishi and Nibe
OSO is a Norwegian manufacturer specialising in cylinders engineered for heat pump systems — built and tested in a climate harsher than Ireland's. The Optima XL HP is factory-recommended by both Mitsubishi Electric Ireland for Ecodan installations and Nibe Ireland for S-series heat pump systems. Its 3.2 m² primary stainless coil and 85mm insulation (the thickest in this directory) result in the lowest standing heat loss of any cylinder listed: 1.15 kWh/24h. Over a year of heat pump operation, that 15% lower standing loss vs a typical copper cylinder saves a meaningful amount of electricity.
200L3.2m² HP coil25-yr warrantyStainless steelVentedSEAI: part of HP grant
⚙️ Specifications
Capacity
200 litres
Primary (HP) coil area
3.2 m²
Cylinder type
Vented (gravity-fed cold tank)
Inner material
Stainless steel (304)
Insulation thickness
85 mm
Standing heat loss
1.15 kWh/24h
Max primary temp
80°C
Immersion heaters
2 × 3 kW
Dimensions (H × Ø)
1480 × 545 mm
Weight (empty)
43 kg
Warranty
25 years
Made in Ireland
No
💰 Pricing & SEAI grant
Cylinder supply price
~€860
Plus installation labour ~€400–€700 · Total installed ~€1,410
💰 Covered by SEAI Heat Pump System Grant (3 Feb 2026)
The cylinder is included as part of your overall heat pump installation cost. The SEAI grant covers the total installed system cost — heat pump, cylinder, controls, pipework and labour — up to:
① Heat Pump Equipment Grant€6,500
② Central Heating Upgrade (inc. cylinder)€2,000
③ Renewable Heat Bonus (fossil fuel switch)€4,000
Maximum total grant€12,500
Apply at seai.ie — receive Letter of Offer before installation begins. BER assessment required (€200 SEAI grant). Homes built before 2007 need Technical Assessment (€200). Installer must be SEAI-registered.
Key highlights
❄️
Norwegian engineering — built for cold climates
OSO designs cylinders for Norway, where heat pumps operate in ambient temperatures of −20°C — significantly colder than Ireland. The thermal engineering and insulation specifications exceed what the Irish climate demands, meaning lower standing losses and better performance in all conditions
🔋
Lowest standing heat loss — 1.15 kWh/24h
At 1.15 kWh/24h, the Optima XL HP has the lowest standing heat loss of any cylinder in this directory. Over a full year (365 days), that's approximately 420 kWh less standing heat loss than a typical copper cylinder — equivalent to about 100 litres of oil saved annually
✅
Dual-brand approval — Mitsubishi + Nibe
Factory-recommended by the two Scandinavian-heritage heat pump brands most popular in Ireland — Mitsubishi Electric Ecodan and Nibe. This means both heat pump manufacturers have tested and approved this specific coil configuration for their systems
🏠 Suitable for
Heat pumpPremium installationHard water areasNordic-climate engineeringMitsubishi and Nibe systems
Installation note: Vented cylinders require a cold water storage tank (usually in the loft) feeding by gravity. If your home doesn't have a loft tank, discuss with your plumber whether a vented or unvented cylinder is more appropriate for your installation.
✅ What we like
Factory-recommended by both Mitsubishi Electric and Nibe in Ireland
85mm insulation — thickest in this directory, lowest standing heat loss (1.15 kWh/24h)
3.2 m² primary HP coil — large area for efficient heat pump heat transfer
Stainless steel — hard water and coastal corrosion resistant
25-year warranty
Norwegian heat pump climate heritage — designed for low-temperature operation
⚠️ Worth knowing
Not manufactured in Ireland — Norwegian production
200L — may be undersized for 5+ person households or high hot water demand
Standard 304 stainless (not duplex) — Kingspan Albion has better coastal corrosion resistance
Higher price than copper alternatives (~€860 vs ~€650)
🌡️ Compatible heat pump brands
The Optima XL HP 200L is compatible with all major air-to-water heat pump brands and is factory-recommended or shipped with Nibe S2125-8 (recommended), Mitsubishi Ecodan (approved). See the Heat Pump Directory for full specifications, pricing and SEAI grant details on all 19 heat pumps available in Ireland.
Mitsubishi Electric EcodanNibeDaikinSamsungVaillantPanasonic
❓ Questions about the Optima XL HP 200L
The OSO Optima XL HP 200L cylinder itself costs approximately ~€860. Installation (remove existing cylinder, connect to heat pump primary circuit, commission immersion backup) adds approximately €400–€700. Total installed cost: typically ~€1,410. This is usually included in the overall heat pump installation quote from your SEAI-registered installer — ask for the cylinder to be itemised on the quote so you can compare against other brands.
In most cases, no — your existing cylinder should be replaced as part of the heat pump installation. Standard cylinders have small primary coils (1.5–2.0 m²) designed for boiler temperatures of 70–80°C. Heat pumps deliver water at 45–55°C and need a much larger coil (typically 2.8–3.4 m²) to transfer adequate heat at the lower temperature. The OSO Optima XL HP 200L has a 3.2 m² primary coil — specifically sized for heat pump low-temperature operation. Using a standard cylinder with a heat pump results in slow reheat, inefficient operation, and higher running costs.
Yes — the cylinder cost is included within the SEAI Heat Pump System Grant (up to €12,500 for houses switching from fossil fuel heating, from 3 February 2026). The grant is applied to the total installed system cost including heat pump, cylinder, controls, pipework and labour — not as a separate per-component payment. Cylinders are not individually grant-funded as standalone items. A BER assessment is required before the grant can be drawn down, and all work must be carried out by a SEAI-registered contractor. The OSO Optima XL HP 200L's ~€860 cylinder cost contributes toward the Central Heating Upgrade element of the grant (up to €2,000).
A heat pump cylinder is typically set to 55–60°C to balance legionella risk with heat pump efficiency. Legionella bacteria cannot survive above 60°C. Most heat pump systems include a weekly legionella protection cycle where the immersion heater in the OSO Optima XL HP 200L raises the full cylinder to 60–70°C. Day-to-day, the heat pump heats the cylinder to the setpoint temperature (often 50–55°C) — a heat pump's COP drops significantly above 55°C. The OSO Optima XL HP 200L's max primary temperature of 80°C accommodates both routine heat pump operation and legionella protection cycles. Your installer will configure the legionella cycle as part of commissioning.
The OSO Optima XL HP 200L at 200L is suited to a typical 3–4 bedroom family home. A heat pump heats the cylinder slowly over 2–4 hours (compared to a boiler's rapid reheat) — so the system is usually programmed to heat the cylinder once or twice daily, storing enough hot water for the day's demand. General guideline: allow 40–50 litres per person per day. For a 4-person household with a heat pump: 160–200L minimum. Homes with high shower use or a bath should consider 200–250L.
For hard water areas (Dublin, Kildare, Meath, parts of Munster) and coastal locations within 10km of the sea, yes — stainless steel is worth the premium. Copper cylinders in high-hardness water areas frequently develop pinhole corrosion after 15–20 years. The OSO Optima XL HP 200L's stainless steel inner resists hard water pitting and coastal salt air corrosion. The cost premium over a comparable copper cylinder is typically €120–180 — which is easily offset by avoiding a cylinder replacement at €800–1,200 installed. For soft water areas (Connacht west coast, most of Donegal), copper is perfectly adequate and the saving is a reasonable decision.
Heat transfer through a coil depends on temperature difference (ΔT), flow rate, and coil surface area. In a boiler system, ΔT is large (boiler at 75°C, cylinder at 55°C → ΔT = 20°C) — even a small coil transfers heat quickly. In a heat pump system, ΔT is small (HP at 50°C, cylinder at 45°C → ΔT = 5°C). With a small ΔT, you need a much larger coil surface area to transfer the same heat. The OSO Optima XL HP 200L's 3.2 m² primary coil — one of the largest available — compensates for the low temperature differential, allowing the heat pump to operate at lower, more efficient flow temperatures without sacrificing reheat time. Standard boiler cylinders typically have only 1.5–2.0 m² coils — using one with a heat pump results in slow reheat and the heat pump working harder and less efficiently.
A cylinder loses heat to the surrounding room through its insulation continuously — this is called standing heat loss. Every kWh of standing heat loss must be replaced by the heat pump (or immersion heater), consuming electricity. A standard copper cylinder might lose 1.5 kWh/24h; the OSO Optima XL HP loses 1.15 kWh/24h — a difference of 0.35 kWh/day, or 128 kWh/year. At 40 cent per kWh (Irish rate), that's approximately €51/year in additional running cost from a poorly insulated cylinder. Over 20 years, that's over €1,000 — making the extra insulation a worthwhile investment.
Yes — OSO cylinders are distributed in Ireland through SRC Ireland and Nibe Ireland's installer network. They are most commonly specified by Nibe and Mitsubishi Ecodan installers. Outside the Nibe/Mitsubishi ecosystem, Joule Cyclone or Range Tribune HE are more commonly stocked by general plumbing merchants. If your installer already works with Mitsubishi or Nibe, ask specifically about the OSO Optima as part of the system quote.
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Your installer will supply and install both the heat pump and the OSO cylinder as a complete SEAI-eligible system. Tell us what combination you need — we match you with up to 3 SEAI-registered installers in your area. Free and no obligation.
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Open your depot to partner fleets — managed EV charging
Truck and van depots can now open their charging infrastructure to visiting partners and contract fleets. Set your energy rate — charge from your heat pump and solar at Pure Energy rates, blend with grid on Smart Energy, or run at full grid speed on Boost Energy. Filter bookings by vehicle category — Car, Van, Truck, Campervan.
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Partner depot access
Open your depot to visiting partners with managed booking — track every session
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kWh & session tracking
Live energy usage, cost per session and cumulative depot totals — all in one dashboard
The OSO Optima XL HP 200L is designed to work with the following heat pumps, solar diverters and smart energy products from our Irish directories. It is supplied as standard with Nibe S2125-8 (recommended) and Mitsubishi Ecodan (approved) installations.
Solar diverters — use surplus solar for free hot water
This cylinder has an immersion heater — which means it can receive free hot water from surplus solar. A solar diverter intercepts solar surplus before it exports to the grid and redirects it straight to your immersion, typically providing 60–80% of annual hot water from the sun. Payback is usually under 18 months.
A 4kWp solar system generates approximately 3,600 kWh/year in Ireland. With a solar diverter redirecting surplus to this cylinder's immersion heater, you can cover 60–80% of annual hot water energy for free — on top of the heat pump doing the heavy lifting.
EV charger + home battery — run everything on solar
Your heat pump and this cylinder provide low-carbon heating and hot water. Add solar panels, a home battery and an EV charger and you can power your car, your heating and your hot water from the same roof — the combined SEAI grants available reach up to €14,600.
A hot water cylinder upgrade is often the first step in a wider home energy transformation. With a solar diverter filling your cylinder for free during the day, the next natural step is an EV — charged overnight on cheap night-rate electricity or from surplus solar. See all 205+ EVs in the EV Vehicle Directory.
💧 Solar hot water + EV: your whole home running on free energy
☀️ Solar diverter
Free hot water
surplus solar → cylinder
🚗 Smart EV charger
Free driving
surplus solar → your EV
💶 Combined saving
~€3,000/yr
hot water + fuel combined
A myenergi Eddi fills your cylinder with free solar. A myenergi Zappi in Eco+ mode fills your EV with whatever solar is left — both share generation data via the Hub so they never compete. View myenergi Eddi →
