Air Source Heat
Pump FAQ Technical Hub

Before installation, your home must have the correct electrical supply for both the outdoor unit and indoor equipment.

See pages 11 & 12 of site preparations document for more information.

A. Outdoor Unit (Heat Pump)

• Must have its own dedicated earthed circuit from the fuse board (no shared circuits).

• Correct fuse / breaker:
  
  • 6 kW → 16 A Type B
  • 10 kW → 20 A Type B
  • 14 kW (single phase) → 32 A Type B
  • 14 kW (3-phase) → 16 A Type B 3P+N

• Armoured supply cable (for short runs, please consult an electrician for upsizing for longer runs):
  
  • 6 kW: 3-core (3×2.5 mm²)
  • 10 kW & 14 kW: 3-core (3×4 mm²)
  • 14 kW 3-phase: 5-core (5×2.5 mm²)

• An isolated rotary switch must be fitted on the outside wall near the heat pump.
• All work must comply with BS 7671 standards.

B. Indoor Equipment

• Cylinder: Dedicated 13 A Type B RCBO circuit.
• Buffer Tank Immersion: Separate 16 A Type B RCBO circuit.

Important If your existing fuse board or meter cupboard does not meet these requirements, Adlår will pause installation until it is upgraded. We can carry out the electrical work for you if requested.

Contact us on 01252 268 669 for a pre-survey or advice.

Before your Adlår Castra heat pump can be installed, a pre-survey is carried out to make sure your site is fully prepared.

Key checks include:

• Location & Clearances Suitable outdoor space with good airflow and correct distances from walls, windows, and neighbours.
• Mounting & Base Solid, level base or bracket with proper condensate drainage.
• Plumbing & Ducting Pipework, cold feed, PRV, and external air intake/exhaust ducting ready.
• Electrical Supply Dedicated circuits from the fuse board for the outdoor unit and indoor equipment (correct fuse ratings, armoured cables, rotary isolator switch, and full BS 7671 compliance).

Important If any of these are not ready, installation will be paused until the work is completed. Adlår can carry out the electrical upgrades for you if requested.

Full checklist Download the complete Adlår Castra Pre-Survey Checks PDF here: 

Contact us on 01252 268 669 to book your pre-survey.

Before your Adlår Castra heat pump can be installed, the following site preparations must be completed:

Key requirements:

• Outdoor Unit Location & Clearances Place the unit outside with good airflow. Keep it more than 5 m from neighbours’ windows. Minimum clearances: 50 cm (one side), 30 cm (sides), 100 cm (top), 30 cm (front), 20 cm (base).
• Base & Mounting Install on a solid, level base (concrete slabs on soft ground or drainage tray on hard surfaces). Ensure good condensate drainage to prevent ice or slip hazards.
• Plumbing Pre-install flow/return pipework, hot/cold water connections for the cylinder, PRV pipework, and balancing valves.
• Air Ducting Prepare external air intake and exhaust ducting in advance (wall, loft, or roof venting). Ducts must be correctly sized and terminated outdoors.
• Electrical Supply Dedicated circuits from the fuse board for the outdoor unit and indoor equipment (correct fuse ratings and armoured cables for your model). An isolated rotary switch must be fitted outdoors.

Important If the site is not fully prepared, installation may be delayed or additional charges could apply. Adlår can carry out electrical upgrades if requested.

Full checklist Download the complete Adlår Castra Site Preparations PDF here

Adlår is fully MCS certified, the UK’s official quality standard for heat pump installations.

What you receive As part of your installation you will be issued with your own official MCS certificate. This is required for the Renewable Heat Incentive (if applicable), future property sales, and warranty validation.

Transferring ownership If you sell or transfer your home, we can easily transfer the MCS certificate to the new owner. Simply provide us with the new owner’s details and we will handle the transfer for you at no extra cost.

Recommended pipe Use ISOFLOW 32mm Double With Cable Ducts – Quadruple Heat Pump (160mm) from Flowsupplies (or equivalent pre-insulated pipe). This includes the flow and return pipes plus built-in cable ducts.

Trench advice

• Ideal trench depth: 600 mm
• Leave 600 mm of pipe above ground at both ends (this gives enough length to connect to the outdoor unit and indoor equipment without joints underground).

Backfill

• Lay a 100–150 mm sand bed at the bottom.
• Place the pipe and cable ducts on top.
• Backfill with another 100–150 mm of sand, then normal soil.
• Mark the trench clearly with warning tape.

If purchasing the pipe yourself Please also buy:

• Correct compression or push-fit fittings for 32 mm pipe
• 2× heatshrink end caps (one for each end of the insulated pipe)

This keeps the insulation fully protected and prevents water ingress.

Tip Using pre-insulated pipe with cable ducts is the quickest and most reliable method. If you are unsure about sizing or layout, contact us before you dig.

See also: Site Preparations & Pre-Survey Checks

Yes – we generally recommend upgrading your radiators where the heat loss calculation shows they are undersized.

Why upgrade? Larger or more efficient emitters allow your Adlår Castra heat pump to run at lower flow temperatures. This improves efficiency, lowers running costs, and delivers better comfort and more even heating throughout your home.

Important note Your heat loss report includes a detailed breakdown of each room, the assumptions made, and the safety margins applied. In many cases your existing radiators may still work adequately. However, upgrading in line with the heat loss report gives you the best long-term performance and efficiency.

Prioritisation If you are upgrading selectively, we suggest focusing on:

• Downstairs rooms (main living areas)
• Rooms with the largest variance (biggest shortfall)
• Hallways and landings

What Space Do I Need for My Adlår Castra Heat Pump?

Here’s the minimum space and clearance requirements for a successful installation.

Outdoor Unit (Aurora II)

• Location: Must be outside with good airflow. Keep it more than 5 m from neighbours’ windows.
• Minimum clearances:
  
  • 50 cm on one side
  • 30 cm on the other sides
  • 100 cm above the top
  • 30 cm in front
  • 20 cm at the base
• Base size (recommended): At least 1200 mm long × 720 mm wide (solid, level concrete slab or plinth with good drainage).

Indoor Equipment (Fjord I Cylinder)

• Needs space for the cylinder, expansion vessels, and pipe connections.
• Full dimensions are in the Unit Dimensions PDF below.

Full details & diagrams Download the complete guides:

• Adlår Castra Site Preparations PDF
• Adlår Castra Unit Dimensions PDF

Cooling with Your Adlår Castra System – Built-in as Standard

One of the biggest advantages of choosing Adlår is that your heat pump comes ready for cooling straight out of the box — with no extra parts, no additional cost, and no complicated upgrades.

Unlike most air-source heat pumps that only heat, the Adlår Castra is a true dual-mode system. It delivers genuine cooling using the same outdoor unit and your Fjord I cylinder — giving you summer comfort as standard.

Two Easy Ways to Cool Your Home

1. Passive Cooling through Your Pipes (Recommended & Simplest) Set the heat pump to the lowest heating curve (HL8). Even in warm weather the system gently circulates cooler water through your underfloor heating or radiators, giving you free, low-energy cooling with almost zero running cost.

2. Duct the Cold Air from the Fjord I Cylinder The cylinder produces cold air (typically 10°C cooler than outside air) as a natural byproduct. You can manually redirect this air inside your home during hot weather by simply adjusting the duct on top of the cylinder. It’s a fantastic way to get extra free cooling in key rooms.

Why Adlår is Unique Most heat pumps require expensive extra kits or separate air-conditioning systems for cooling. With Adlår you get both powerful heating and effective cooling from one high-efficiency system — saving you money on installation and on your energy bills all year round.

Planning tip for best results During installation we can advise on lagging pipes and positioning the cylinder duct for maximum cooling benefit. Just mention you’d like to make full use of the cooling features.

Ready to enjoy comfortable summers as well as warm winters? Your Adlår system is designed to do both — beautifully.

Your Fjord I cylinder must be ducted to draw fresh air from outside and safely expel the cold air it produces. Proper ducting is essential for efficiency, safety, and compliance with MCS and Ofgem regulations.

General requirements

• Duct size: 160 mm (this is the default and recommended size)
• Two separate ducts:
  
  • Intake – brings in external air to the cylinder
  • Outtake – expels cold air (typically 8–12°C cooler than intake air)
• Maximum duct lengths (with minimal bends):
  
  • Rigid duct: up to 24 m
  • Flexible duct: up to 12 m
• All ducting should be insulated to prevent condensation.

External termination options

• External wall cowls/grilles
• Flat roof terminals
• Pitched roof terminals

Passive cooling bonus The cold outtake air can be manually redirected inside your home during warm weather for free, low-energy cooling (see our Air Con with Fjord I Cylinder guide).

Important Ducting must always source air from external ambient air — not from inside the house or inhabited spaces.

Full guide & diagrams Download the complete Adlår Castra Ducting PDF here: https://adlar.co.uk/wp-content/uploads/Adlår-Castra-Ducting.pdf

Adlår does not use glycol or antifreeze valves on the central heating circuit of our systems.

Our approach to freeze protection

Instead, we rely on a robust, passive design that provides excellent protection without any of the downsides of chemical or mechanical solutions:

• All external pipework is a continuous run of high-quality pre-insulated pipe rated to withstand temperatures as low as -50°C.
• The outdoor heat pump continuously circulates and gently heats the central heating system, maintaining latent heat in the pipes at all times.
• The system includes multiple built-in electronic anti-freeze protections that activate automatically if needed. This is why it is critical the main power to the unit isn't turned off at the isolation switch or on the consumer unit.

This design keeps the system simple, efficient, and highly reliable under normal UK winter conditions.

Why we don’t use Glycol Adding propylene glycol (typically 25–30% concentration) significantly increases the viscosity (thickness) of the heating fluid — usually 2–3 times higher than plain water. This leads to:

• Higher pressure drops in the pipework
• A typical reduction in flow rate of 15–25% (or more) for the same pump speed
• Reduced heat transfer efficiency
• Higher electricity consumption by the circulation pump

Because of these performance penalties, glycol is not used in our systems.

Why we don’t use Antifreeze Valves Automatic drain valves are also unnecessary. Our insulated pipework and active low-level heating provide far more effective protection without the risk of valves failing or introducing air into the system.

Extremely rare freezing risk The only realistic way the central heating circuit could freeze is during a prolonged power cut lasting more than 24 hours combined with sustained sub-zero temperatures.

In this very unlikely scenario:

• We recommend safely draining the central heating system to prevent any damage.
• If you experience a power cut lasting more than 20 hours during freezing conditions, please contact the Adlår office immediately on 01252 268 669. We will guide you through the safe draining process step-by-step.

This design gives you the best of both worlds: excellent freeze protection and maximum system efficiency and performance.

What it does It captures sludge, magnetite (black iron oxide), and other ferromagnetic debris that naturally builds up in the central heating circuit. This protects the heat pump, circulation pump, valves, and pipework from blockages and wear.

Benefits

• Maintains optimum flow rates and system efficiency
• Reduces the risk of breakdowns
• Extends the life of your entire heating system

The filter is easy to service – simply remove the magnetic core and flush out the collected debris during annual maintenance.

Your Fjord I hot water cylinder can be fitted with a powered electric anode (also called an impressed current anode).

What it does Unlike traditional sacrificial magnesium anodes that gradually dissolve, the electric anode uses a small electrical current to protect the stainless steel tank from corrosion. It also helps balance the water’s mineral content by reducing the effects of calcium, chlorine, and heavy metals.

Benefits

• Dramatically extends the life of your cylinder
• Maintains better water quality
• Requires no replacement (unlike sacrificial anodes)

This is one of the reasons Adlår cylinders achieve such high reliability and longevity.

Adlår offers water conditioners as an optional whole-house water conditioner (it is not a water softener).

How it works

Water conditioners use  galvanic/electrolytic technology to change the structure of dissolved calcium carbonate (limescale) so it stays suspended in the water and does not stick to pipes, cylinders, heat exchangers, or fixtures.

Key advantages

• No salt, no chemicals, and no power required
• No maintenance or refills for up to 7 years
• Keeps all the healthy minerals in your water (unlike a softener)
• Protects your heat pump, cylinder, boilers, showers, and appliances from scale build-up

It is especially useful in hard-water areas to maintain system efficiency and reduce future maintenance.

Short answer: Almost always NO.

In the vast majority of homes, your existing internal pipework (15 mm and 22 mm copper or plastic) is perfectly suitable for the Adlår Castra heat pump. We design the system to work efficiently with typical UK retro-fit pipework.

When pipework upgrades are rarely needed

Upgrades are only considered in a few specific situations:

• Very long pipe runs that restrict flow
• Heavily corroded, scaled, or damaged pipes
• Extremely undersized pipes causing poor flow (very rare in modern homes)

During your pre-survey, our engineer will check flow rates and pipe condition and let you know immediately if any minor changes are recommended.

What we always upgrade

• External underground pipe: We always install new pre-insulated 32 mm pipe (rated to -50°C) between the outdoor unit and indoor equipment.
• Emitters (radiators or underfloor heating): This is the upgrade we recommend far more often than pipework, as larger emitters allow lower flow temperatures and much better efficiency.

Bottom line Unlike some heat pump companies that insist on ripping out and replacing all your pipework, Adlår focuses on practical, cost-effective solutions. Most customers keep their existing internal pipes and see excellent performance and low running costs.

See also: Should I Upgrade My Radiators (Emitters)? Site Preparations & Pre-Survey Checks

Adlår deliberately does NOT use buffers or low loss headers on most  system — and there’s a very good reason.

What is a Low Loss Header (or Buffer Tank)?

A low loss header (or buffer tank) is a separate vessel that hydraulically separates the heat pump from the rest of the heating system. Traditional heat pump installers often add one so the heat pump can keep running even when individual zones or the hot water cylinder call for heat.

Why we don’t use them

• They create a 4°C temperature loss — this is the exact penalty assumed in the official BS EN 12831 heat loss standard. That loss means the heat pump has to work harder and run at higher temperatures.
• They reduce efficiency — the heat pump can no longer deliver heat directly and continuously to your radiators or underfloor heating.
• They cause short-cycling and higher bills — the heat pump spends more time turning on and off instead of running steadily at low temperature.
• They add unnecessary cost and complexity — extra components, extra pipework, extra heat loss, and more things that can go wrong.

Adlår’s smarter “Inline” design

Our dual-mode Castra system is engineered so the heat pump can supply space heating and hot water simultaneously without ever needing a buffer or low loss header. Heat goes straight from the heat pump into your emitters with zero temperature penalty and no interruption to space heating.

Result:

• Lower flow temperatures
• Higher efficiency
• Quieter operation
• Lower running costs
• Simpler, more reliable system

Most homes do not need a buffer or low loss header. Adding one is usually a sign the system hasn’t been designed correctly for a heat pump.

Short answer: Stop insulating the heating pipes that run inside your home — it often makes almost no difference to your energy bills.

Why you can stop insulating internal pipework

Your Adlår Castra heat pump runs at much lower temperatures than a traditional boiler. Any heat that escapes from the flow and return pipes inside the heated part of your house (the thermal envelope) still warms the rooms it passes through.

Insulating these pipes:

• Saves very little energy
• Costs time and money
• Can even make the system slightly less efficient in some cases

What you should insulate

• External underground pipe (between the outdoor unit and indoors) — this is already supplied as pre-insulated pipe by Adlår.
• Any pipes that run through unheated spaces (loft, garage, crawl space, etc.).
• Pipes when using cooling mode (to prevent condensation).

Adlår best practice

1. Focus on the big wins: low heat curve, keep zones open, leave the system on 24/7.
2. Only insulate pipes that are losing heat outside the areas you want to heat.
3. For cooling in summer: ensure any visible internal pipes are properly lagged to avoid condensation.

Most customers who remove unnecessary internal pipe insulation report the same (or better) comfort with no noticeable increase in running costs — and one less job to worry about!

Ideal “Perfect World” Setup

1. One always-open zone per manifold / pump group On each zone section or manifold, keep one pump (with signal cable wired back to the heat pump) and one permanently open zone — ideally the largest or coldest room. This zone stays open at all times and always calls for heat. It ensures constant flow through the system and allows the heat pump to run at its most efficient low-temperature heat curve.
2. Other zones controlled by air-temperature thermostats All remaining zones use actuators on the manifold, controlled by good room air sensors (e.g. Neostat or any Smart Life compatible thermostat). These thermostats only open their zone when the room actually needs heat.
3. Floor sensors – only where needed Use a floor sensor only on underfloor heating (UFH) zones with temperature-sensitive finishes (wood, engineered wood, or tiles that could be damaged by high temperatures). For radiator zones you do not need floor sensors.

Why this setup is best for Adlår

• Maintains excellent water flow at all times → prevents E37/E51 errors
• Allows the heat pump to run at the lowest possible heat curve (best efficiency)
• Gives you per-room comfort without constantly opening/closing zones
• Works perfectly with Smart Scenes in the Smart Life app for automatic heat curve adjustments

Practical advice for your rewire

• Wire the “always-open” zone and its pump directly so it is always energised when the heat pump is running.
• Wire all other zone actuators to their respective room air thermostats.
• Make sure your thermostats are Smart Life / Tuya compatible so you can create Smart Scenes that gently adjust the heat curve based on room temperature (instead of turning zones on and off).

This configuration gives you the best of both worlds: reliable flow for efficiency + smart per-room control.

Many people coming from traditional gas boilers are used to turning radiators or whole zones off to “save energy”. With an Adlår Castra heat pump, heavily zoning your system is one of the worst things you can do.

Why heavy zoning causes problems

• Closing too many zones or valves dramatically reduces water flow → this is the #1 cause of E37 and E51 errors.
• The heat pump is forced to run hotter and short-cycle (turn on and off frequently) instead of running steadily at low temperature.
• Efficiency drops and your electricity bills can actually go up.
• Heating becomes uneven and less comfortable across the house.

The shocking truth Running with most zones open is far more efficient and comfortable than constantly opening and closing them. Heat pumps are designed for constant, low-temperature flow — not the on/off behaviour that worked with old boilers.

Best practice instead

1. Set all room thermostats high (or 2–3 °C above current room temperature) so most zones stay open.
2. Optimise your heat curve until you achieve the right comfort level (see our Heat Curves guide).
3. Always keep at least one main or larger zone fully open at all times — this maintains good flow and lets the heat pump run at its most efficient setting.

Once you do this, many customers are surprised how much quieter, more even, and cheaper the system becomes.

See also: Secondary Pumps & Zone Control

Your Adlår Castra system may include secondary circulation pumps (for upstairs, downstairs, or different zones). These can be controlled in two ways:

• Directly by the heat pump, or
• By your existing thermostat/zone control system (e.g. Heatmiser, Hive, etc.)

What we normally do

If you already have a working zone control system (such as Heatmiser), we usually leave it in place. Your existing thermostats will continue to open and close zones and turn the secondary pumps on and off as before.

How to optimise your system

1. Set all room thermostats to maximum (or at least 2–3°C above current room temperature). This opens every zone valve and calls for heat, keeping the secondary pumps running continuously.
2. Now fine-tune your heat curve (see our Heat Curves guide). Find the lowest curve that still gives you comfortable warmth throughout the house.
3. Once you’re happy with the heat curve, you can (if you wish) start closing some zones again.

Efficiency tip The most efficient way to run the system is to keep all (or most) zones open and let the heat pump work at the lowest possible temperature. Frequent opening and closing of zones usually means the heat pump is running too hot and less efficiently.

Best practice if you still want to close zones Always keep at least one main zone or a larger/colder zone fully open (always calling for heat). This keeps the secondary pumps running, maintains good flow throughout the system, and lets you run the heat pump at its most efficient temperature while still delivering excellent comfort.

See also: Heat Curves Explained

Adlår offers all-inclusive warranty packages designed to give you complete peace of mind with your Castra heat pump and Fjord I cylinder for many years.

Standard Warranty (Included Free with Every System)

• 2 years parts cover for manufacturer defects
• Covers the outdoor unit and indoor components supplied by Adlår
• Does not include annual servicing, maintenance, optimisation, or call-outs

Gold Warranty (Recommended)

• Up to 5 years full parts and labour
• Annual servicing and maintenance included
• System efficiency checks and optimisation
• Priority engineer response
• Full access to the Adlår Castra customer app and support

Platinum Warranty

• Up to 15 years full parts and labour
• Everything included in the Gold package
• Remote system monitoring by Adlår engineers
• Advanced smart controls and ongoing performance optimisation
• The most comprehensive long-term protection available

Warmth Guarantee (Included with All Plans)

If your heating or hot water system does not perform as designed (e.g. the house doesn’t reach the agreed comfort levels), Adlår will return and resolve the issue at no extra cost — this goes beyond a normal parts-only warranty.

Why choose an All-Inclusive plan?

• Predictable running costs with included servicing
• Expert support from the same team that designed and installed your system
• No hidden costs for call-outs or repairs
• Long-term protection (up to 15 years)

All warranties are backed by Adlår’s in-house team — no third-party handovers.

This is completely normal and nothing to worry about.

The figures shown on the BUS consent request are the VAT-inclusive (gross) values. These represent the full replacement value of your Adlår Castra heat pump system and are used for insurance purposes — so the correct total insured value is recorded on the official paperwork.

However, because your installation qualifies for VAT exemption under the Boiler Upgrade Scheme, you will only ever be charged the lower VAT-exempt amounts.

For example:

• BUS consent request may show higher VAT-inclusive figures
• You will only pay the VAT-exempt prices (£8,592 and £1,092 in your case)

Adlår installs a dual heat pump system (Aurora II for heating + Fjord I cylinder for hot water) because it solves one of the biggest challenges with single heat pump setups: delivering high hot water demand efficiently without compromising space heating efficiency.

Key Advantages

Efficiency Comparison (SCOP)

Key insight: Lower flow temperatures = dramatically better efficiency. Adlår’s dual system allows the heating heat pump to stay at lower temperatures most of the time.

Test Standards Advantage

• Outdoor heat pumps are tested under EN14825:2022 at cold air temperatures (~2°C).
• Adlår’s Fjord I indoor cylinder is tested under EN16147:2017 at realistic indoor temperatures (7°C/20°C).
• Result: Fjord I achieves COP 3.802 at 20°C/15°C — outperforming most outdoor heat pumps on the market.

In-Line vs Low Loss Header

Single heat pump systems typically use a low-loss header, which causes heat mixing and temperature loss — especially problematic at the low temperatures heat pumps use.

Adlår’s inline design eliminates this, delivering:

• 5.75% lower running costs compared to low-loss header systems
• More consistent temperatures at emitters
• Higher real-world SCOP

Hot Water Challenge with Single Heat Pumps

Single heat pump systems face several real-world inefficiencies:

• Hot water production pauses space heating
• System must ramp up to higher temperatures to recover
• Pipework losses between outdoor unit and cylinder
• Efficiency drops significantly during and after hot water cycles
• Sometimes triggers immersion heaters

Adlår’s dual system avoids all of these issues by dedicating a separate heat pump (inside the Fjord I cylinder) to hot water.

Real-World Example

Customer: 3-bed detached house, EPC D, 115m², 24/7 heating

Even with an 8.57°C colder average outdoor temperature on the Adlår test day, the dual system performed dramatically better.

Summary

Adlår’s dual heat pump approach delivers:

• Higher real-world efficiency (especially for hot water)
• Better comfort (no heating interruptions)
• Lower running costs
• Longer equipment life (heat pumps run at lower, steadier loads)
• Future-proof performance with passive cooling capability

This is why Adlår believes the dual system is the best — and only — way heat pumps should be installed for UK homes with meaningful hot water demand.