ᐅ Reducing Energy Consumption in Older Homes

Hello everyone,

We are buying an older building with an energy rating of G. The current owners have demonstrably done a lot of work in recent years, including installing new windows and replacing and insulating the roof. There is also a solar system for domestic hot water.

We are therefore wondering why the energy consumption is still so high. The realtor and the owners explained that the energy consumption certificate only records the actual consumption over the past months. Since nine people (energy users) lived there during that time, the consumption was naturally that high. They said it would be different for us, as soon-to-be three residents :-)

Is this generally accurate? And are there common insights on where most energy is lost in an older building (around 100 years old)? I am considering hiring an energy consultant.

Thanks for all your answers!

Best regards,
Ramos

Is an energy performance certificate based on consumption or demand available? It’s best to look up the difference online. This seems to be a consumption-based certificate.

Consider whether heating needs are lower with three people compared to nine. Heating energy demand depends more on user behavior than on the number of occupants (only electricity and water usage will be less with fewer people).

A rating of G would mean 200–250 kWh per square meter (m²) of usable floor area, or about 300 kWh per square meter (m²) of living area.

With new windows and a new roof, I would expect a rating between D and E.

Is the value for primary energy or final energy?
What type of heating system is installed?
What kind of walls and basement ceiling are there? How old are the windows really (the production date is printed on the edge of the glass in the silver spacer)?

Given this consumption and these factors, an energy consultation could be worthwhile. The most affordable first step might be to contact a consumer advice center for an initial assessment.

Hello dertill,

thank you for your detailed response. We have an energy performance certificate based on actual consumption; we understand the difference compared to a demand-based certificate, as it was explained to us. That’s why the real estate agent and the owner said it probably relates to the high number of occupants.

I can imagine it like that. While it’s generally best not to completely turn off heating in any room—whether there are two or nine people living there—but to keep some heat everywhere, it does make a difference if everyone turns their heating up fully in their own rooms or not. At least that’s how I understand it as a non-expert :-)

The final energy demand is 210 kWh/m²*a, and the primary energy demand is 234 kWh/m²*a. The windows were replaced within the last one to three years. I don’t have precise information about the walls. The central heating system runs on gas; additionally, there is a solar system for hot water production and a water-bearing fireplace.

Best regards,
Marius

I would consult an energy advisor. Considering the overall purchase price, spending a few extra euros is definitely worthwhile.

Ramius schrieb:
While you should generally avoid letting any room (whether there are two or nine occupants) go completely unheated and therefore maintain some level of heating everywhere, it does make a difference whether each person turns the heating fully up in their own room or not.

If the building is used fully, it doesn’t matter whether 3 or 9 people live in it. If you don’t use one “wing” of the building, energy consumption will of course decrease, but not significantly.

If you lower the room temperature from a consistent 21°C (70°F) to 17-18°C (63-64°F) (lower usually doesn’t make much sense and can also be risky from a building physics perspective), you save roughly 5% of the energy per degree Celsius for the cooler area.
Example: 50m² (538 sq ft) with 200 kWh/m² at 21°C lowered to 18°C = 50m² * 200 kWh/m² * 0.05 * (21-18) = 1,500 kWh/year.

Compared to 40,000 - 60,000 kWh (how large is the house?), this is not much.

If the current occupants prefer living at 23°C (73°F) throughout the house, that could add about 10% to the total energy use.
There is also a reduction in hot water consumption, about 500 kWh/year per occupant, but this will be small here since roughly 50% of hot water is probably supplied by solar thermal systems.

Is the hydronic fireplace included? Check the energy certificate under fuel sources. Probably not, since primary energy is higher than final energy.

Don’t forget: more people also produce more waste heat (100-200 W per person) and use more appliances (dishwasher, washing machine, TV, oven/stove), too.

I wouldn’t have too many illusions and would discuss this with a professional. You won’t be overheating the house, but the figures do suggest there are still some small savings possible, or that current users simply prefer to live year-round as they did last summer.

If you plan to move in initially without renovation (I don’t know the overall condition of the house), you could live there for a year first and see how the heating performs.

Forget all statements from realtors and owners – they want to get rid of the place, not help you save energy. In a 100-year-old house, energy literally leaks everywhere. Energy class G should mean over 200 kWh/m²*a (over 200 kWh/sq ft*yr), which is no real fun for your wallet...