We can choose between a Viessmann split unit (plus ventilation) and a Stiebel Eltron combined system (including ventilation) from our house provider. Both are air-to-water heat pumps.
What I find on this topic are mainly considerations about space or noise, which makes sense. However, Iâm also interested in how efficient these systems actually are. I only find general statements that there is little difference in efficiency between split and combined units, but from a thermodynamics perspective, that doesnât make sense to me:
Split units have intakes located outside the house with diameters of 60â80 cm (24â31 inches) to draw in enough air. The more air you intake, the less energy needs to be extracted from each volume of air, which increases efficiency. A combined unit, on the other hand, only has a 30 cm (12 inches) duct to the outside, which significantly reduces airflow. This means the air has to be cooled much more to extract the same amount of energy. Therefore, in my opinion, it can never operate as efficiently as a split unit.
However, I find zero statements addressing this. No one seems to be concerned about it, and I canât be the first person considering this. Am I mistaken, or do you have different insights on this topic?
Thanks in advance! If you have other aspects to compare these two types, I would also be very interested.
What I find on this topic are mainly considerations about space or noise, which makes sense. However, Iâm also interested in how efficient these systems actually are. I only find general statements that there is little difference in efficiency between split and combined units, but from a thermodynamics perspective, that doesnât make sense to me:
Split units have intakes located outside the house with diameters of 60â80 cm (24â31 inches) to draw in enough air. The more air you intake, the less energy needs to be extracted from each volume of air, which increases efficiency. A combined unit, on the other hand, only has a 30 cm (12 inches) duct to the outside, which significantly reduces airflow. This means the air has to be cooled much more to extract the same amount of energy. Therefore, in my opinion, it can never operate as efficiently as a split unit.
However, I find zero statements addressing this. No one seems to be concerned about it, and I canât be the first person considering this. Am I mistaken, or do you have different insights on this topic?
Thanks in advance! If you have other aspects to compare these two types, I would also be very interested.
In our old house, we had the Tecalor THZ 504 (which is basically identical to the one from Stiebel Eltron), a combined unit.
In the new house, we have a split system from Viessmann.
In terms of noise, I notice only minor differences. In the old house, the Tecalor was responsible for the sounds, while in the new house it is the separate ventilation system. The noise level is comparable.
We were satisfied with the Tecalor. I found it surprisingly affordable; in the second year, we spent around 50-55⏠per month for heating, ventilation, and hot water. It was probably a mild heating season, but still quite economical.
We havenât lived in the new house long enough yet to provide meaningful comparison data. The first winter is still ahead, and even more so the second. At the moment, electricity consumption seems significantly higher than in the old house. However, it is a larger house and still damp, as it has just been occupied.
Unfortunately, I canât comment on the technical differences or compare pipe sizes, as I lack the expertise.
In the new house, we have a split system from Viessmann.
In terms of noise, I notice only minor differences. In the old house, the Tecalor was responsible for the sounds, while in the new house it is the separate ventilation system. The noise level is comparable.
We were satisfied with the Tecalor. I found it surprisingly affordable; in the second year, we spent around 50-55⏠per month for heating, ventilation, and hot water. It was probably a mild heating season, but still quite economical.
We havenât lived in the new house long enough yet to provide meaningful comparison data. The first winter is still ahead, and even more so the second. At the moment, electricity consumption seems significantly higher than in the old house. However, it is a larger house and still damp, as it has just been occupied.
Unfortunately, I canât comment on the technical differences or compare pipe sizes, as I lack the expertise.