We also have a combi unit with 8.4 kW output and controlled living space ventilation with heat recovery. Our hot water tank has 235l, I think that fits. In most devices, hot water preparation is prioritized.
Yes, combined units are simply designed for exactly those 75 or 80% of standard families. It usually fits well, and especially prefab house manufacturers have zero work with the sizing. The dimensioning of the underfloor heating is done by their manufacturer, from that the heating load is derived, the next larger combined unit of choice with or without ventilation next to it, commissioning is done by the manufacturer. End of story. But if you come with your own requirements or deviate from the standard, it often looks bleak. And for some, 3 kids are enough for that ;)
No problem in that regard, we are building freely planned with the architect, this was just the first proposal from the heating engineer. That’s why I want to basically discuss the topic again with him, but at least beforehand have already gained a basic understanding of the subject.
The size of a combined unit is simply limited. More water cannot be accommodated in the space.
An external storage tank is not much more expensive. You have to have the space, and the system with a small storage tank definitely has its advantages, because it is considerably faster recharged and delivers "bath temperature".
So you would rather stick with the small storage tank?
We also have a combined unit with 8.4 kW output and controlled residential ventilation with heat recovery. Our hot water tank is 235 liters, I think that fits.
For most units, hot water production is the priority
Are the 8.4 kW A7 or A2 heating output? Do you already have the unit in operation? How many people, what kind of water consumption?
I would only take a larger storage tank if there is a particularly high hot water demand or if, for example, there is space in the basement for a separate storage tank anyway. If it ever needs to be replaced, that is certainly easier than repairing or even replacing a combination unit.
Thanks for your hint. So it doesn't necessarily have to be a larger storage. Unfortunately, there is only limited space in the technical room, but I will still discuss the issue during the appointment with the heating engineer.
Are the 8.4kW A7 or A2 heating capacity? Have you already put the device into operation? How many people, what kind of water consumption?
Heating capacity at A-7/W35 (EN 14511): 8.34 kW
Heating capacity at A2/W35 (EN 14511): 5.16 kW
Heating capacity at A7/W35 (EN 14511): 4.40 kW
More in the datasheet
Device has been in the house since March, then screed program etc., move-in 10.08., adjustment 11.08.
Currently still 2 people, approx. 165 m2 living area
Thanks for the information. The air-to-water heat pump offered to me has 7.7kW A2 and 8.5kW A7, so comparable to or slightly more powerful. I assume you currently have no issues with too little hot water for two people?!