I live in a building of 8 apartments, in Belgium. We share a communal fuel oil boiler in the basement to provide hot water and heat. For the latter, each apartment has radiators through which a hot liquid flows. We do not have gas pipes running to each apartment, but there is an unused gas main in the basement.

I would like to upgrade this system to a cleaner solution, still providing hot water and heat. We could consider a shared solution or independent for each apartment. What are the best alternatives to consider? Thanks.

  • 1
    What problem are you trying to solve? Heat generation or heat distribution?
    – Aron
    Commented Dec 2, 2015 at 5:07

3 Answers 3


TL, DR Solar thermal with a gas burner for peak demand. Possibly improved isolation.

First, you need exact data on how much heat you need, and when, during the year and during each day.

This should help you get an idea if the insulation of your house can be improved. Once you have the numbers, ask here for a first orientation. Without seeing the house (preferably through a thermographic camera) we will only give you a balpark estimate though.

Then, I'd lok at the following:

Solar thermal - how much collector surface can you actually mount on your house? If it's 8-storey, you will have limited roof space but maybe a south facing fasade without much shadow? Once you have a realistic grip on how much collectors you could mount, do a conservative calculation how much thermal power this will bring you over the year (again, you want a graph of thermal power vs. time in the year) and on days representative of different periods.

See how much of your demand you can actually cover with solar thermal, decide if its worth it. Or rather: decide if it's worth to go forward with examining the possibility.

Next, look at peak heat demand and peak heat production, to get an idea how much heat storage (a huge water tank in your cellar) you will need. My gut feeling is that you will store heat for 12h to a day at the utmost, everything beyond that will be ridiculuosly large.

Look at how much of your heat demand you cannot satisfy from (stored solar), this wil stil come from your boiler. I suggest swapping for a natural gas boiler since those emit less CO2. The gas burner must be sized to supply you total heat demand, as you could have days with very bad weather and practically no sun. The burner will only be active when you need heat in but the storage tank is cold.

You will definitly need a professional to do the installation and to properly size all components. You will need high quality (well insulated) collectors to achieve high temperatures, else you'll have problems 'marrying' the solar thermal to your existing heating.


You could definitely switch to an efficient gas boiler system with proper controls to run "cleaner" and more efficiently. Depending on gas/oil prices in your area, this may or may not be economically beneficial (short or long term).

Varying with your current setup, electrical prices in your area (and their generation method) you could also change about your hot water system to be more insulated when stored (lose less energy), be on demand (may or may not be viable depending on distances), or use electricity some or all of the time to heat water.

If you are just looking for cleaner but similar replacement, a well controlled gas fired boiler that was also used to heat a highly insulated hot water storage tank would be a good place to start. You could take the installation period as a chance to view/change the zones in the existing system and possibly do insulation work to minimize heat lost during transmission.

  1. If you have it available switching to natural gas will produce less CO2.

  2. If you have renewable energy surpluses, then TES (Thermal Energy Storage) makes lots of sense. You use MUCH larger water tanks, and heat it electrically when there is a surplus of power. Your air systems can be heated with hot-water fan coils -- cheap conversion.

Look at roof mounting solar power. Tie into the grid. Sell power to the grid during the day. Buy it at it's minimum cost during the night to heat the tanks for the next day.

  1. Even without renewable, you can size a heat pump to the average demand instead of peak demand. It will be far more efficient that way.

If you do the heating with a heatpump, you can also create cold water or ice for summer air conditioning using the same system.

Wikipedia TES https://en.wikipedia.org/wiki/Thermal_energy_storage

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