Ground source heat pump or air-to-water is a question every builder of a new house reaches at the latest when the design is on the table and the size of the technical room has to be confirmed. Supporters of both solutions have argued in forums for years, and brand advertising does not help, because it talks about the device, not about the house and the plot.
This article sets out six things that really decide the question and says at each point how it works in a Happy Home house.
The two solutions in brief
An air-to-water heat pump takes heat from the outdoor air and transfers it to the heating water that circulates in the underfloor heating pipes and heats the domestic hot water. The device consists of an outdoor unit next to the house and an indoor unit in the technical room.
Geothermal heating, that is a ground source heat pump, takes heat from the ground: either from a vertical borehole or from a horizontal collector dug into the plot below the frost depth. The temperature of the ground is stable all year round, so the system works evenly even on the coldest days. Both solutions suit water underfloor heating and heat-recovery ventilation, which are standard in our houses. The technical solutions are on the construction info page.
1. Plot size and soil
The first decider is the plot. Geothermal heating needs either a borehole, which fits a small plot but whose depth and permissibility depend on the soil and groundwater protection, or a horizontal collector, which needs a large free area of ground where nothing can be built later and no deep-rooted trees planted. On a small urban plot the only options are often a borehole or an air-to-water solution.
An air-to-water heat pump needs only a place for the outdoor unit: sheltered and out of the wind, away from the neighbour’s bedroom window, and placed so that condensate can drain away. Our architect reviews the plot conditions before the heating solution is confirmed, because it affects both the technical room and the site plan.
2. The heat demand of the house
The second decider is the house itself. The more airtight and better insulated the envelope, the smaller the heat demand and the less the difference between heat sources matters. The measured air leakage rate of Happy Home houses has stayed between 0.13 and 0.35, and all our houses are in energy class A or B. In such a house either type of heat pump gives a result several times better than usual.
Geothermal heating therefore gives its biggest advantage in a large house and a very cold region, where the heat demand is high; in a smaller airtight house the efficiency difference matters less in money. What the energy class means is explained in our article on the energy class A house.
3. Winter efficiency and the running costs of a ground source heat pump
The third decider is efficiency in cold weather. The efficiency of an air-to-water heat pump drops as the outdoor temperature drops, because heat is harder to extract from the outdoor air; on the coldest days an electric backup heater helps. Ground source heating works with the stable temperature of the ground and keeps its efficiency even throughout the winter.
The difference in running costs comes from exactly this: geothermal heating uses less electricity over the year to produce the same amount of heat. How large the difference is in euros depends on the electricity price, the size of the house and the family’s habits. The principle is that the deeper solution buys lower running costs with a higher upfront investment.
4. Upfront investment and installation
The fourth decider is installation. Ground source heating means drilling a borehole or digging a collector, piping to the house and the equipment in the technical room. Drilling a borehole may need a municipal permit and conditions depending on groundwater protection, which should be checked before the design. Installing an air-to-water solution is faster and cheaper, because there is no groundwork.
With Happy Home the heating solution is agreed together with the house and is part of the turnkey offer. What the offer includes is explained in our article on the turnkey house price, and the share that technical systems take of the total is easier to see once you know what makes up the price of a CLT house. We send a model-based sample price list on request, with an explanation of what the price includes, and a more precise offer follows a consultation.
5. Working together with underfloor heating and ventilation
The fifth decider is the system as a whole. Both types of heat pump work most efficiently with a low heating water temperature, which water underfloor heating allows: a large heating surface, a low temperature. Room-by-room control lets the bedrooms stay cooler and the living room warmer without raising the temperature of the whole system. How the loops, the manifold and the controls are built into a new house is covered in our article on planning underfloor heating in a new house.
Heat-recovery ventilation takes the heat back from the outgoing air, so the pump only covers the remainder. The trio of heat pump, water underfloor heating and heat recovery is what gives our houses low heating costs whichever heat source is chosen.
6. Space, noise and maintenance
The sixth decider is daily life. The outdoor unit of an air-to-water heat pump makes a sound when running, which is quiet on today’s equipment but worth considering when choosing its location. Geothermal heating is silent outside and quiet in the technical room. Both need a technical room with space for the device, the hot water tank and the ventilation unit.
For maintenance both are simple: an annual inspection, filter changes on the ventilation and the manufacturer’s service intervals. The equipment carries the manufacturer’s guarantee, and we provide after-sales service. A general description of how a heat pump works is on Wikipedia.
Solar panels next to either
Either solution uses electricity, and both can be paired with solar panels or the Solarstone roof solution, which reduce the electricity you buy. The most sensible time to plan them is during construction, while the roof structure, pitch and cable routes are still open. In winter, when the heat demand is highest, there is little sun, so the panels do not replace the pump but reduce the annual electricity cost. Output, orientation and payback are discussed in more detail in our article on solar panels for a house.
How to decide
If the plot allows a borehole or a collector, the house is large and you want the lowest running costs, geothermal heating is a strong choice; if the plot is small, the house is compact and airtight and the upfront investment has to stay lower, an air-to-water solution is sensible and reliable. If you would like the architect to assess the options on your plot, send us the plot documents through the contact page and we will go through the heating solution together.
When does the heating solution have to be decided?
During the design stage, which with us takes one to three months on average, and before the building permit application, which in practice takes two to three months. The heat source affects the technical room, the site plan and the roof, so it is cheapest to fix it while those are still on paper.
Can cooling be added to the same system?
Yes, cooling can be added to the house if you want it. Say so during the design, because it affects the equipment choice and the pipe routes.
Which heating solutions does Happy Home offer?
An air-to-water heat pump, ground source heating and solar panels, with cooling as an option. We recommend choosing the heating together with the house rather than after it, so that the technical room, the roof and the plot are designed as one whole.
