ᐅ Question about Heat Demand Calculation and Supply Temperature

Hi,

We’re about to start building soon, and regarding the underfloor heating and flow temperature, I received a suggestion from an expert and wanted to get your opinions here.

Brief summary of the house: a 152 sqm (1,637 sq ft) city villa with underfloor heating, 30cm (12 inches) Ytong exterior walls, 3 solar collectors, and heating via a gas boiler.

The expert recommended installing the underfloor heating with closer pipe spacing throughout the entire house so it can operate at lower flow temperatures (35°C (95°F) instead of 40°C (104°F)). There are initially higher costs for the extra work and materials, but it saves money in the long run because the gas boiler doesn’t need to reach as high a temperature and therefore uses less energy. The investment is expected to pay off after a few years. Additionally, this approach keeps options open for switching later to an alternative heating system (heat pump, etc.) since these usually cannot deliver the 40°C (104°F) flow temperature required, and it’s uncertain which cost-effective alternatives to gas will be available in the future.

As a layperson, this sounded reasonable to me at first. What do you think?

Regards

Always operate with the lowest possible flow temperature. Closer spacing should only be a minor additional cost.

With our heat pump, the flow temperature in winter has not exceeded 28°C (82°F) in the last two years.

As for the gas boiler, it doesn’t really matter whether it’s 35 or 40... nevertheless, I would still design it to be as low as possible.

Ok, thanks. That’s what I wanted to hear 🙂
I will have it designed accordingly then.

Since there is already a similar post, I’ll continue here.

We are also facing the decision of whether to install the underfloor heating pipes at a spacing of 15-20cm (6-8 inches) or 10-15cm (4-6 inches). The additional cost for the closer spacing amounts to €640 (net).

House details: 117m² (1,259 sq ft) total area minus utility room, resulting in 107m² (1,152 sq ft) of living space to be covered with underfloor heating; exterior walls made of calcium silicate blocks plus brick veneer (approximately 45cm (18 inches) total thickness); 3 solar panels; 300L (79 gallons) hot water tank; the gas condensing boiler (model ?) is from Vaillant.

According to the calculations, the following data apply for the closer pipe spacing:
Supply temperature 38.2°C (100.8°F)
Average return temperature 31.2°C (88.2°F)
Total heating load 6062 watts
Underfloor heating output 5882 watts
Pipe length 1143m (3752 feet)
13 heating circuits

As this is quite technical for me and the advice from the plumbing company has not been very helpful, other than “both options are possible,” I would like to ask here whether it makes sense to install the heating loops closer together, or if I should save the additional cost and install the pipes with the standard spacing (15-20cm (6-8 inches))?

Unfortunately, I do not have the data for the standard pipe spacing.

I find the pipe length quite high for the small area – we have a spacing of 10–15cm (4–6 inches) depending on the room and laid just under 1300 meters (4265 feet) with 22 or 23 heating circuits and around 240 square meters (2580 square feet) of heated floor area...