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Ecocent Systems

Understanding Exhaust – Air Hot Water Systems Versus Full Air Source Heat Pumps

As the UK moves toward cleaner, greener home heating solutions, many homeowners are being offered what appear to be cutting-edge technologies that promise both efficient heating and hot water. High on this list are systems that integrate the concept of heat recovery from indoor air – often referred to as exhaust-air heat pumps or systems like the Ecocent.
These products are marketed as if they “heat your home and provide your hot water” while using waste heat from the indoor air. But the reality often falls somewhere between the marketing spin and what’s actually delivered in your household. Let’s break down how these units really work, compare them to traditional air source heat pumps (ASHPs), and highlight some crucial considerations (Ecocent Systems).

What Are Exhaust – Air Heat Pump Cylinders?

These systems – call them Ecocent-type cylinders or other branded exhaust-air hot water products—sit inside your home and pull air through, extracting some of its heat before venting it outside. They’re essentially combining the idea of a hot water cylinder with a small heat pump attached, running off the air you’d otherwise send out via ventilation.

Ecocent Systems: What They Claim to Do

• Provide hot water very efficiently, often with a coefficient of performance (COP) of around 3 to 4. This means for every unit of electricity you put in, you get 3 to 4 units of heat out.
• Help with ventilation by replacing stale, moisture-laden indoor air with fresh air at a fraction of the energy cost of simply dumping heated air outside. In fact, they can reduce the cost of ventilation to about a quarter of what it would cost if you just flushed warm air away without any heat recovery.

The Reality:

• They Don’t Really “Heat Your Home”: While the marketing might imply these units contribute to space heating, in practice they primarily heat your hot water. The heat they use to achieve their high efficiency in hot water production is largely pulled out of the home’s indoor air, which was already heated by another source. Over time, if no new heat is introduced from outside (like from an ASHP, solar gains, or occupants), it becomes a closed loop: you’re essentially moving the same heat around. There’s no magic energy creation. Without a dedicated heat source like a proper ASHP or boiler, you might not see the real heating savings you were expecting.
• Ventilation at a Lower Cost: The genuine strength of these systems lies in their ability to provide the required ventilation without as much wasted energy. Instead of letting the warm indoor air escape, the system recovers much of its heat. That’s beneficial compared to simple extraction fans, which just blow warm air outside. But this is not the same as introducing new, “free” heat into the home. It’s a more efficient use of energy you’ve already paid for.

Comparing Two Common Setups

1. The Dedicated ASHP + Ecocent for Hot Water
   In this scenario, you install a proper air-to-water heat pump outside. This ASHP provides your main space heating, pulling in free energy from the outside air. Even in cold weather, it can achieve a respectable COP of around 3.5, meaning it’s genuinely adding value by using renewable, outdoor-sourced heat.
   Then you pair that with an Ecocent (or similar unit) for hot water. The Ecocent recovers some of the heat that would have been lost through ventilation and uses it to produce hot water at a COP of around 4. This combination can significantly reduce overall energy costs, because you’re using the ASHP to efficiently heat your home and the Ecocent to efficiently heat your water from what’s essentially captured waste heat.
2. The Ecocent + Electric Boiler Combo
   Here, instead of pairing the Ecocent with a proper heat pump, someone installs an electric boiler for space heating. Electric boilers convert electricity to heat at a COP of 1—no efficiency gains. While your hot water might be efficiently produced by the Ecocent, your space heating is expensive and no more efficient than old-fashioned direct electric heating. The net result? You might feel like you’re paying far more than if you’d had a proper ASHP or even a gas boiler (though the latter isn’t a low-carbon solution).

Ecocent Systems: When Expectations and Reality Collide

Imagine a couple in a newly built, well-insulated home. They were originally quoted and promised a system involving a full air source heat pump outside plus an efficient hot water solution using indoor air recovery. They expected dramatically lower heating bills and a sustainable, integrated setup.
But what they ended up with was a hot water cylinder with an internal heat pump (similar to an Ecocent) plus a simple electric boiler for the heating load. The hot water may have improved efficiency compared to a standard electric immersion, but their space heating was now coming from a high-cost electric boiler. Instead of enjoying consistently low bills, they found themselves paying significantly more than anticipated. The marketing materials suggested a streamlined solution that would use “renewable” heat, but without the ASHP drawing energy from outside air, they were mostly just recirculating indoor heat or relying on direct electricity consumption.

Ecocent Systems: Do These Units Have a Place?

Absolutely. These exhaust-air hot water units do provide a valuable service, especially where you need to maintain good indoor air quality. By recovering much of the heat that would be lost through simple mechanical ventilation, they ensure you’re getting some return on your heating investment. They shine in environments where mechanical ventilation is essential, and where you’d otherwise waste warm air straight out of the house.
Their “green” credentials hold up best when paired with a system that actually brings in renewable heat from outside—like a properly specified ASHP.

Practical Considerations in the UK Context

Ecocent Systems: Space Requirements

One of the biggest shifts in moving away from combi boilers is the need for a dedicated hot water cylinder. For heat pumps, including these integrated units, a cylinder is a must because heat pumps can’t instantly provide hot water like a combi can. This often means finding 1 square meter of floor space and significant vertical space, frequently a big ask in smaller homes.
If there’s an integral garage or a loft available, homeowners often consider placing the cylinder there. But these unheated spaces can lower the overall efficiency of the hot water cylinder. For loft installations, horizontal cylinders are sometimes chosen, but these are typically less efficient still, pushing up running costs.

The UK’s Home Heating Landscape:

• Most UK heating companies are small, with fewer than 10 employees.
• Replacing a gas boiler takes less than a day for a single engineer (assuming electrical circuits are ready).
• Replacing or installing a heat pump can take a team of three engineers 3 days, or 6–9 days of work altogether. This scale-up in complexity and labor is part of the reason careful planning is required.
• Heat pumps need more space for cylinders and careful planning to ensure hot water availability and efficiency.

How Boxergy Supports Homeowners

At Boxergy, we’re dedicated to making your energy cheaper, greener, and smarter. We’re specialists in air source heat pumps, solar PV, batteries, and EV chargers, and we maintain all the relevant certifications including MCS, FGAS, and Gas Safe. Our approach focuses on:

• Delivering the Right System for You: We don’t just drop in an Ecocent and an electric boiler and call it a day. Instead, we evaluate your home’s heat demand, ventilation needs, and space constraints to recommend a solution that genuinely meets your expectations.
• Ongoing Support and Maintenance: Renewable systems aren’t “fit and forget.” We offer service and maintenance packages to ensure your system runs at peak performance. That includes help with smart tariffs, so you can minimise costs by using stored solar energy or tapping into cheaper off-peak electricity.
• Maximising Savings and Comfort: By combining an air source heat pump for space heating and a well-placed hot water cylinder, we help ensure that the system’s advertised COPs turn into real-world savings. We’ll help you avoid situations where you’re left with a high-cost electric boiler as your primary heat source.

Exhaust-air hot water systems like the Ecocent have their merits – they’re great at reducing the cost of necessary ventilation and can efficiently produce hot water. But they’re not standalone heating solutions. When marketed as if they can “heat your home” on their own, this can lead to disappointment, especially if the heating load is ultimately handled by an electric boiler.
The truly beneficial path is pairing such a system with a proper ASHP for the main heating load, ensuring that while you ventilate, you’re not wasting energy and you’re truly tapping into renewable heat from outside. Proper planning, accurate sizing, and professional guidance can help homeowners achieve the comfort, cost savings, and sustainability they’re promised.

At Boxergy, we aim to bridge the gap between marketing and reality. We’ll help you navigate the options, ensure you understand what each component does, and support you through installation and beyond. That way, you get the system that’s right for your home and your wallet – no surprises, no disappointment, just genuine greener, smarter energy solutions. Ready to start your eco journey? Talk to our experts today!

Author: Jim Laidlaw, CEO & Founder at Boxergy

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