ᐅ Old oil heating system for a two-family house

Hello everyone,

I own a two-family house with an old oil heating system, which I would like to replace in the near future. What would you recommend here, including any alternatives and with regard to available subsidies? Roughly, what kind of cost range should I expect?

Here are the facts and details:

Two-family house, built in 1971
Occupied by 4 people
Solid construction, exterior walls not insulated, insulation planned for the coming years
Partially new windows, to be replaced soon
Apartment 1: 200m² (2,150 sq ft), Apartment 2: 85m² (915 sq ft)
Oil heating system, Heimax NOK 33, 1993
Underground tank, 10,000 liters (2,640 gallons)
No gas connection available
Total consumption approximately 3,000 liters (790 gallons)
Solar thermal collector 2003, SK500 N, 15.4m² (166 sq ft), storage tank 750 liters (200 gallons)
Apartment 1 has a wood stove, around 8 kW

I hope I have provided all the necessary information.

Thanks, regards

Hello,
My mother recently went through this topic in her house (about 250 sqm (2700 sq ft) split into two apartments) two years ago. In the end, it only made sense to install a new oil boiler. Since these are now only available with condensing technology, a smaller liner had to be installed in the chimney, a drainage option had to be created in the boiler room, and so on. Overall, she paid around 15,000 euros.

Heat pumps and similar systems are not suitable for you; for those, you need a well-insulated house with underfloor heating.

Your consumption isn’t actually that bad — about 30,000 kWh for 285 sqm (3,070 sq ft) of living space. A modern house of that size would still require 15,000–20,000 kWh.

The new heating system won’t reduce consumption by much, at best about 10%, no more. So I’d keep it until it breaks down and only replace it then. If you’re lucky, it will last until the building boom cools down a bit, and prices come down as well.

Best regards,

Andreas

First, complete the planned insulation and then determine the actual heating load. If no new radiators are planned, install new windows specifically in rooms with the highest heating load or where the highest supply temperatures are needed to maintain warmth.

Once the heating load is known, you can consider replacing the heating system. For now, I would continue running and maintaining it.

My dad has a similar issue. A few years ago, he insulated the exterior of his house. Now he has replaced the small radiators with new, larger ones. These have twice the depth and width. Fortunately, there is no problem with space. He said that in the future he plans to heat with low-temperature systems and replace the old heating with an air-source heat pump when possible.

In my opinion, you should:

• Avoid adding external insulation.
• Keep the heating system until it breaks down.
• Insulate the roof and replace the windows (if not done already).

Anything else would not be economically or environmentally reasonable.

If you ever need to replace the heating system, oil, gas (higher investment due to the tank), or maybe in a few years a micro or nano combined heat and power unit could make sense. The latter only if you have a good electricity consumer—an electric car, neighbor, pool heat pump...

Additional note: My parents’ house is quite comparable to yours, only somewhat older. 300 sqm (3,230 sq ft), built in 1961, oil heating from 1988, additional wood stove, and solar thermal system. The roof is new, and the second set of windows are still good. Consumption for three people is 1,600 liters (422 gallons) of heating oil and 4–5 cubic meters (141–177 cubic feet) of firewood. I wouldn’t touch the exterior; the chimney sweep advises to keep the heating running until it’s decommissioned.

heizer_18 schrieb:
Family house built in 1971
Occupied by 4 people
Solid construction, exterior walls not insulated, insulation planned for the next few years

Insulating exterior walls is usually the most expensive way to save energy. Unless you do it yourself or a renovation is already needed due to damaged plaster, the payback period is often more than 10 years, sometimes not achieved at all.

A building from 1971 is probably no longer made of solid bricks but rather aerated concrete, hollow bricks, or concrete blocks. What is the wall thickness? Is it faced with brick cladding or plastered? Do you have building documents showing the exterior wall structure?
Depending on the construction method, U-values for buildings from that year range between 0.6 and 1.4 W/m²K, which makes a big difference in whether exterior wall insulation is worthwhile.

Regarding the heating system, if gas is available at the property boundary, I would get a quote for that as well. A gas boiler is usually cheaper than a new oil-fired central heating system, so you save the extra cost there. In operation, gas is generally cheaper and easier to manage. Definitely continue using the solar collector, and replace the storage tank if it’s defective.
Generally, keep the current system running until you decide what to do with the windows. It’s best to install triple-glazed windows with warm edge spacers. As already mentioned, make sure to insulate the roof properly and, if needed, insulate the basement ceiling from below – this is cost-effective and efficient.

Only after that should you replace the heating system, sizing it smaller according to the new heat load.

Subsidies: KfW Program 430 grants for individual measures such as windows (U-value <0.95), gas boiler, roof (U-value <0.14), each covering 10% of total costs.
Or KfW Program 430 heating package grant: 15% of costs if a hydraulic balancing is done, plus 15% for other eligible individual measures carried out simultaneously.

Depending on the federal state, regional development banks or local authorities may offer additional subsidy programs that can often be combined with KfW programs.

So it’s best to carry out everything together: