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Gondwana Green Heat — home

Heat Pumps

Air, ground, ventilation and compact units — fitted since 2004, and designed around the building rather than the brochure.

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Four types, one mechanism

The difference is where the energy comes from

Dave fitted his first heat pump in 2004 — a 5kW NIBE air‑to‑water unit heating a tropical palm and cycad house up the Ettrick valley, half an hour from Peebles, with underfloor pipes embedded in concrete and growing beds on top. It is the most unusual heat‑pump project we have ever done, in a thoroughly inhospitable location, the winter of the install dropping to −20°C.

We work with four main types. The mechanism is essentially the same in all of them; the difference lies in the energy source they draw on — air, water, ground or exhaust air.

Which one suits depends on the heat load in kW, the local climate, the outdoor space available and whatever systems the building already has. What follows is what each type is good at, and what decides between them.

Air source

The most common type in the UK, and around for decades. Installed outdoors, using outside air to boil the refrigerant.

Ground source

Using the stable warmth held in the ground, through trenches, pond and lake loops, or boreholes.

Ventilation cylinders

A hot‑water cylinder or buffer tank with a compact heat pump on top, drawing its air through ductwork — typically from MVHR or waste stale air.

Compact MVHR units

Ventilation, space heating and hot water in one cabinet, running off the warm air the house is already exhausting.

Air source

Designed around a temperature that keeps moving

Outside air runs from around 25°C in summer to −5°C in winter. In warmer conditions the refrigerant boils more vigorously and the unit produces more energy; in colder conditions it produces less. That is why a correct heat‑load calculation and an understanding of the local climate decide whether a system performs all year or only for part of it.

Heat pumps are most efficient at lower flow temperatures, which is why underfloor heating suits them — it runs cool by nature. Radiators work very well too, but they have to be sized for low‑temperature operation, which usually means larger radiators than a traditional boiler needed.

Works alongside

Ground source

Steadier, and dearer to put in

Below roughly 900mm the soil temperature barely moves across the year. We take that energy out through pipes laid in trenches or, where space is short, pond loops, lake loops or boreholes — the last of which also suit a site that is having a water borehole drilled anyway.

Because the ground temperature is stable, output is consistent and efficiency is generally better than air source. Cold snaps do not touch it.

The cost is the catch. Trenches, boreholes and water loops mean time, machinery and labour, so a ground source system is dearer to install and cheaper to run — especially in the coldest months.

What most people choose

Air source, with something behind it

Most customers still go for air source, often supported by a second heat source such as a wood stove or a pellet stove.

That pairing lets you lift the house temperature through the short spells when an air source unit is working hardest, and keeps the running costs down across the year.

The compact end

Ventilation cylinders and all‑in‑one units

Ventilation heat pump cylinders

One of the simplest and most impressive heat‑pump technologies available. Designs vary between manufacturers, but the principle holds: a hot‑water cylinder or buffer tank with a compact air source heat pump mounted on top, drawing its air through ductwork — either fresh from outside, or the waste air leaving an MVHR system.

On ventilation heat pump cylinders the efficiencies are extremely high, with COPs typically between 4 and 6 — 400 to 600% efficient. The heat pump warms the cylinder for hot water and, in some models, a limited amount of space heating: usually 20–40m² of underfloor.

Many also carry indirect coils for solar thermal, or connections for a small pellet or boiler stove.

The limit is output. These units are small — typically 1.5–4kW — which suits compact homes, well‑insulated properties, and any building already fitted with MVHR.

Most of the enquiries we get for ventilation heat pump cylinders come from commercial buildings and large properties where a full air or ground source system would cost too much to install, or is simply not feasible logistically. A ventilation heat pump cylinder can be slotted straight in to replace a conventional hot water cylinder, at a fraction of the operating cost — especially alongside MVHR.

Compact MVHR units with a heat pump built in

The first compact MVHR heat‑pump system Dave installed was a Genvex unit over twenty years ago, in a low‑energy Scandinavian kit home. It combined MVHR ventilation, space heating through the supply‑air ductwork and a hot‑water cylinder in one package.

Today's units follow the same principle: an MVHR system with a small air source heat pump in the cabinet, using the warm exhaust air to boil the refrigerant — which is what makes them so efficient. The heat goes straight into the fresh‑air supply duct as warm supply air, and most include a cylinder, making the whole thing a single heating‑and‑ventilation solution.

They are physically larger than a standard MVHR unit, roughly the size of a fridge‑freezer. And as with the ventilation cylinders, the heat pump inside is small — typically 1–3kW, with some models accepting solar PV input.

In a low‑energy home, a Passive House or a compact well‑insulated space, this is a straightforward and efficient answer without a separate heat‑pump installation.

Which type suits comes down to heat load, climate and what is already there.

Tell us about the building and what it needs to do, and we will work out which of the four fits — and what to pair it with.

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