ᐅ Condensation or puddles on pipes – despite controlled mechanical ventilation and dehumidifiers

Hello everyone,

In August of this year, we took over a single-family house from the general contractor. It was planned together with us. A brief overview of the situation: we have 202 m² (2172 sq ft) of usable floor space (approximately 185 m² (1991 sq ft) of living area + 17 m² (183 sq ft) for technical/utility rooms), two full stories, an unfinished hipped roof, and no basement. Heating is provided by a heat pump with underfloor heating, although some rooms (e.g., technical/utility rooms) are unheated. We also installed a central ventilation system from Helios (controlled residential ventilation 500EC), including a ground-source heat exchanger (brine circuit) and an enthalpy heat exchanger. All rooms receive fresh air supply or have extracted air—this applies, for example, to the technical/utility rooms. Our ventilation system runs continuously at the set “nominal level.”

Now to the problem: since the outdoor temperature dropped below 10°C (50°F), we have experienced heavy condensation on practically all pipes in the technical/utility rooms. This includes, for example, the fresh water supply pipes, the pipes of the brine circuit, and also the supply air duct of the ventilation system. The condensation is sometimes so severe (worsening with colder temperatures) that puddles form at the base of the pipes and under critical points of the horizontally running pipes. I have attached several photos that show the situation at that time. The relative humidity was around 55–60%. From my understanding, this is relatively high but not excessively so—especially for an unheated room where washing and drying take place.

The general contractor has attributed the issue to excessive humidity due to construction moisture and advised us to ventilate more frequently. We naturally questioned why we have a ventilation system costing nearly 26,000 EUR if we still need to ventilate manually. Their response was, “It’s only at the beginning because of the construction moisture.” I would like to point out that in all other rooms of the house, under similar temperatures, the humidity levels are around 40–45%. So, I cannot detect any significant construction moisture elsewhere in the house.

Since we both work and cannot ventilate throughout the day, we purchased a larger dehumidifier and additionally ventilate in the mornings and evenings. Since then, the humidity has remained consistently below 50% (usually around 47–48%). However, the condensation issue has hardly improved or only marginally. As a result, the general contractor insulated many of the pipes. You can find photos of this in the attachments as well. The effect is that the condensation now appears on other uninsulated spots or that water is accumulating behind the insulation (when I press against the insulation, my fingers get wet).

Both the contracted installer and Helios are at a loss as to what else can be done. In the current condition, I consider mold growth within a few years to be likely, which of course must be avoided. Do you have any ideas on what else I can try? Many thanks in advance!

Regards

Micha