ᐅ 190L vs. 309L Hot Water Storage Tank for a Household of Four People

Good morning everyone!

We are currently contracting the heating and plumbing work for the construction of our single-family house (the shell is already underway). Here are some basic details about the building:

- 2 full floors, approximately 180 m² (170 m² (1,830 sq ft) living area, 10 m² (110 sq ft) utility room)
- no basement
- gable roof
- KFW 55 EE standard (including air-to-water heat pump, photovoltaic system)
- occupied by 2 adults and 1 child (eventually 2 children in total)

The plan is to install an air-to-water heat pump combined with a photovoltaic system and underfloor heating.

Provider A offers the following for the air-to-water heat pump:
Vaillant brand with a 190-liter (50-gallon) hot water tank plus all necessary accessories and installation for €28,560.00 net.

Provider B offers the following:
Weishaupt brand with a 309-liter (82-gallon) hot water tank plus all necessary accessories and installation for €22,628.20 net.

My question: Do you have any experience with the size of the hot water tank? Provider A says that 190 liters is sufficient for a 4-person household. It should be mentioned that we like to take longer showers, so we are not exactly the most economical in this regard.

Thank you in advance for your opinions and experiences.

I would definitely lean towards the 300L (79 gallons) tank. Taking 2-3 good showers uses up 190L (50 gallons) already. Besides, the 300L (79 gallons) tanks are also significantly cheaper….

Sinosch31 schrieb:

My question: Do you have experience with the size of the hot water tank? Provider A says that 190 liters is enough for a household of four. It should be noted that we like to take long showers, so we are not exactly the most economical in that regard.

Provider A is mistaken.
From personal experience with three children (and myself as a part-time dad): when the three kids come back from the stables and shower (long hair uses a lot of water under the rain shower), the 300-liter (80-gallon) tank is left at only about 25-30°C (77-86°F). That means only lukewarm water is left for me.
Definitely install a 300-liter (80-gallon) tank.

Sinosch31 schrieb:

Good morning everyone!

We are currently awarding the heating and plumbing contract for our single-family home construction (the shell is already underway).
First, here are some key details about the building:

- 2 full floors, approximately 180 m² (1,938 sq ft) total (170 m² (1,830 sq ft) living area, 10 m² (108 sq ft) technical room)
- no basement
- gable roof
- KfW 55 EE standard (including an air-to-water heat pump and photovoltaic system)
- to be occupied by 2 adults and 1 child (later a total of 2 children)

The plan is to install an air-to-water heat pump combined with a photovoltaic system and underfloor heating.

Provider A offers the following for the air-to-water heat pump:
Brand VAILLANT with a 190-liter (50-gallon) hot water tank including all necessary accessories + installation for 28,560.00 euros net.

Provider B offers the following:
Brand Weishaupt with a 309-liter (82-gallon) hot water tank including all necessary accessories + installation for 22,628.20 euros net.

My question: Do you have any experience with the size of the hot water tank? Provider A says that 190 liters (50 gallons) is sufficient for a household of four. It should be mentioned that we like longer showers, so we are not exactly the most economical in this regard.

Thanks in advance for your opinions/experiences.

We only have 150 liters (40 gallons) for 3 people, and I enjoy long showers. So far, that has always been sufficient, even for taking a full bath followed by a quick shower. However, we have a gas boiler that can replenish the hot water tank at 15 kW output! Your heat pump, on the other hand, will have a significantly lower output depending on the water temperature.

If you fill a somewhat larger bathtub with 240 liters (63 gallons) and the air-to-water heat pump heats the water to 55°C (131°F), you would need at least a 160-liter (42-gallon) tank plus 80 liters (21 gallons) of cold water to achieve 240 liters (63 gallons) of bath water at 40°C (104°F). After that, the heat pump will only be able to slowly reheat the tank, likely providing around 3 to 5 kW at that temperature level, which is a very slow flow rate. For comparison, an electric tankless water heater typically has a power rating of 22 kW and can supply a shower "in real time" (although not for very high flow rates like a rain shower).

With a 190-liter (50-gallon) tank, you basically have reserves for one full bath or about a 15-minute shower (15 x 16 liters/min (4 gallons/min) at 40°C (104°F)). Anyone using the bathroom afterward will either get lukewarm water or have to wait for hours to reheat.

Alternatively, everyone takes short showers.

The 309-liter (82-gallon) tank offers significantly more reserves (i.e., a full bath plus 15 minutes of showering afterward) at the cost of slightly higher standby losses.

Sinosch31 schrieb:

Good morning everyone!

We are currently contracting the heating and plumbing work for our single-family home (the shell construction is already underway).
Here are the key details about the building:

- 2 full floors, approximately 180 m² (170 m² (1830 sq ft) living space, 10 m² (108 sq ft) utility room)
- no basement
- gable roof
- KfW 55 EE standard (including air-to-water heat pump, photovoltaic system)
- occupied by 2 adults and 1 child (eventually 2 children)

The plan is to use an air-to-water heat pump combined with a photovoltaic system and underfloor heating.

Provider A offers the following for the air-to-water heat pump:
Brand VAILLANT with a 190-liter (50 gallons) hot water storage tank and all necessary accessories + installation for 28,560.00 euros net.

Provider B offers the following:
Brand Weishaupt with a 309-liter (82 gallons) hot water storage tank and all necessary accessories + installation for 22,628.20 euros net.

My question: do you have any experience regarding the size of the hot water storage tank? Provider A claims that 190 liters is sufficient for a household of four. It should be mentioned that we tend to take longer showers, so water usage won't be particularly economical.

Thank you in advance for your opinions and experiences.

I would also choose the offer with the larger storage tank. Heating water with a heat pump takes longer than with a gas boiler.
If multiple people shower one after another, there will be enough warm water available.

Heating 200 liters (53 gallons) of water with an air-to-water heat pump can take up to one hour.

Sinosch31 schrieb:

Do you have any experience with the size of the hot water tank? Supplier A says that 190 liters is enough for a household of four.

Go for the 300-liter tank!
It could get complicated for you otherwise 🙂 It’s frustrating when comfort suffers. In our old house, we had 80 liters: while one person was washing dishes, another was in the 170-liter bathtub, and only covered with warm water.

Sinosch31 schrieb:

It should be mentioned that we like to take longer showers.