Heating the right way


  1. What will you find here?
  2. Heating costs money - your money!
  3. Heating losses and gains
  4. Generating and consuming heat
  5. Public buildings: heating with the windows open


1. What will you find here?

An easy explanation of the basic connections between heating and ventilation: technical know-how is the basis for saving energy. At the end, you will find some terrifying examples!

To avoid problems in the heating, air-conditioning, and ventilation business,
the basic rule is
'Use water for heating and air only for ventilation!'


2. Heating costs money - your money!

As a tenant, you are now spending an average of 25% of your income on rent and charges.
As a landlord you are able to share out charges (of which heating costs are a part) among your tenants. But stop and ask yourself: do high charges make my property an attractive proposition?
As a house-owner, it's you who has to pay high heating bills.

A certain level of technical know-how is a good idea if you are interested in saving. You don't need to be an expert: sometimes knowing just one trick of the trade to economize a few hundred euros. Not a bad reimbursement! And you can also save tax at the same time..
      If you're not able to take the job on yourself, but are still interested in saving money, put the matter in our hands. You will receive our proposals.

I know that my car does 35 miles to the gallon, but how much fuel does my house burn in a year?

How far do you get on one litre of oil or 1 m3 of gas?
A few approximate numbers: one litre of petrol, 1 litre of "extra-lite heating oil" or 1 m3 of H-gas yield approx. 10kWh of energy. A free-standing house, which, using about 100kWh/(m²*a), is already cheap to heat, consumes 2000 litres of oil per year for a living area of 200 m². This oil is burned over about 1500 hours. This means 1 litre of oil will only last 45 minutes. The normal case is that free-standing houses get through 4000 litres of oil (1 litre every 22 minutes). Look at the figures: of techem!
      Annual consumption is officially defined in terms of kilowatt hours per year, but the figure "litres per year" is easier to remember and simply one-tenth of the kWh figure.

Does the 3-litre house already exist? Yes, but only pioneering individuals live there!
The statistics of the people who calculate the heating cost show that we're even still a long way from the 10-litre house! The 3-litre car is being built, but our houses remain at the top of the global warming hit parade with up to 20 litres/m!

This is how average consumption pro m for multi-occupied houses looked in 2001:

Type of house
"Heating only"
Annual oil consumption
in L/m
Annual gas consumption
in L/m
2-5 multi-occupied house 14.1 14.1
6-10 multi-occupied house 13.1 13.5
11-50 multi-occupied house 12.4 13.0

Type of house
"Heating and hot water"
Annual oil consumption
in L/m
Annual gas consumption
in L/m
2-5 multi-occupied house 17.8 17.8
6-10 multi-occupied house 17.5 17.6
11-50 multi-occupied house 17.0 17.5
Source: www.minol.com 2002 (135,000 clients).

How was it before?

'We have observed about 40% reduction in energy consumption over the logged 26 years (1977/78 until 2002/03),' reports techem in its (German) Annual Overview 2005 (375,000 clients).
Mean consumption of heating energy
Source: techem characteristic energy values, 2005 figures.
Current mean consumption of heating energy in multi-occupied residential houses in Germany is 158.5kWh/m² or climate-corrected, 159.2 kWh/m² for oil, 161.8 kWh/m² for gas und 123.8 kWh/m²for long-distance energy. The difference between oil or gas and long-distance energy is about 75%. Techem regards this value as the Annual Utilisation Ratio (AUR) of heat generation. The standard deviation around 75% would be interesting to know...

Impact of size of building

Size of building and consumption
Source: techem Specific german energy values, report 2005
Above you can see heating oil consumption in litres/m² related to the heated living area. On the left are the multi-occupied houses, which are most expensive in consumption and cost. It is clear that improvements are especially demanded here and massive savings are achievable. A cut to a 'poor' value of 12 litres/m² can be achieved by technical optimisation alone, i.e. a reduction of 55%..


Even though German average consumption has fallen steadily, we are currently allowing ourselves in a 75% majority the luxury of 12 to 24 litre houses. Only 15% consume less than 12 liters/m². Houses heated by natural gas previously consumed more, but now consume the same as oil-heated houses. The technology of condensing boilers, adopted more readily in the case of gas because it involved fewer problems in operation, may be one reason why.
      We achieved a consumption of 7.79 liters/m²*a. Many Germans prefer to save money by buying low-consumption fluorescent bulbs (2%) rather than making economies in heating consumption (89%). More energy saving tipps.
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3. Heating losses and gains

How do heating losses come about?
To keep your room at the right temperature when it is cold outside, your heating system has to deliver as much heat as you are losing through walls, windows and openings. Just think of it as pouring water through a sieve: you have to keep pouring in as much water (or warmth!) as is flowing out at the bottom to keep the sieve full (or the room warm!). Sealing the openings prevents heat outflow.
      Today, the biggest holes in your sieve are still the windows: 37% of your heating exits your apartment that way. Long-term measurements have proved that good insulation of window-frames and the use of triple-glazing will reduce your heating losses by 40%.
      A sieve empties immediately, while in a room the rate at which room temperature decreases depends on the capacity of the walls to hold heat. At the same time, walls store heat, protecting us against adverse weather conditions.
A corner and its temperatures
Temperature gradient in an outside wall angle
[Source: RWE Construction Guide]
Room temperature is the temperature of the interior of the wall, and outdoor temperature is the temperature of the exterior of the wall. The temperature gradient in the wall (and its insulation) is the difference in temperature between the inside and the outside of the wall. When outside temperatures are low, it is important to know where the temperature gradient is highest. This is where an area of dew-point temperature arises. When the air temperature drops to this temperature, the air releases the water contained in it as vapor in the form of drops. Make no mistake: depending on the quantity of air circulating, this can add up to liters(!). The wall first becomes damp, later mouldy.
At local humidity (Germany), this happens at about 13ºC. If the temperature in the corners of the room sinks below +13ºC, mould will soon appear, because humidity condenses in these places. Appropriate action would be to insulate the corners from the outside and to ventilate frequently.

Where do heat gains come from?
They come from the radiation of the sun and from other sources external to your heating system, such as appliances which are on. Even the human body radiates heat, approximately 100W (you will feel this in meetings!).
      Solar radiation, even if only diffuse, will increase temperature at once. You will notice this in a greenhouse. Windows facing south help to capture solar radiation, and for the same reason should be kept small when facing north.
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4. Generating and consuming heat

Heating systems consist of 3 parts:
  1. the heater,
  2. the distribution network,
  3. the consumer components.

4.1 The heater

Generally, heaters consist of a fuel reservoir (oil tank) or the gas connection and one or more boilers. In long-distance energy systems, the entire heat generating element consists of the interconnecting station.
      The "brain-center" of the system is control and adjustment of burner and boiler. This is where you decide how high your domestic consumption at the end of the year will be. Correct adjustment here will point to the most important possibilities of saving: what you don't burn, you don't pay for. Our questionnaire will give you hints about what adjustments to make.
      There are hundreds of models of boilers, which can be combined with every conceivable kind of oil burner. The best thing is to by a unit which has been optimized by the manufacturer. Units include gas boilers which are supplied as ready-to-run boilers.

Boilers are of all sizes; the question is, which size is the right size? You can calculate the size with a heat requirement calculation, or you can make a rough estimate. A boiler of correct dimensions will burn all day at the lowest long-term average minimum outside temperature. In this case, you have got the right size! Only a well selected boiler-burner combination has long burner running times. Only in the two operating conditions, burner running and boiler cold will you have no losses while the system is not running. Ideally, you will need a modulating burner, able to reduce its power from 100% down to 50%. This is particularly achievable with gas as the fuel and the burner will only cost 50 euro more than a conventional one-stage on/off burner.
      The only catch: adapting the power of the burner requires its own controller costing nearly 500 euro. Such a burner is thus only worthwhile for large heating plants.
      To achieve a better total Annual Utilisation Ratio (lower energy cost) all you normally need to do is to install the right kind of 2-stage burner. More than 50% of maximum power capacity are actually used in a single month(!). In central Europe, 36% of the annual heating work is consumed when the temperature outside is between 0...+ 5ºC.
In our latitudes, how many hours per year does a burner actually run?
(the longer the running time, the better)
  • 700...1000 hours when the heat generator is oversized and/or serious problems arise in the hydraulic system
  • 1000...1900 hours in the case of a well-designed heat generator
  • 2000...4000 hours, if optimized and 2-stage or modulating
How long does a burner have to continue burning once started?
  • If it runs 2...10 minutes, output is oversized and/or there are serious problems in the hydraulic system. Make sure you check how long your burner needs to get properly running after the start! A gas burner is no improvement
  • Running times of 15 minutes indicate an incorrectly balanced system.
  • If it runs for about 20...30 minutes, the system is properly balanced.
Experience tells us that burner running times of under 10 minutes when the outside temperature is about +10C is a sure indication that the system is potentially very wasteful. It is time to do something!

4.2 The distribution network

The distribution network brings the heat transfer medium (usually water) to the heat consumers, which are the heat sources for you as a user, and the takes them back to the boiler (a little less warm than before). Some important components are in the room where your boiler is located, such as heat circuit distributor, pumps, expansion tank, safety valve, refilling device, etc... The rest of the distributing network is concealed (hopefully insulated!) in the house.
      The pump, which is the heart of the system, builds up the pressure to keep the water flowing. The faster it flows, the less time it has to cool down in the radiators, and the warmer it returns to the boiler. This is known as the temperature difference between flow and return. This difference should be 20C with radiator heating (15C according to the latest standard), and 10C for under-floor heating systems and heater registers in air-conditioning systems. Because pump outputs are generally too high (experts say 3 times too high!), the temperature you measure will be lower than the calculated value, which only obtain when the system starts up in the morning.
This is a big chance to make immediate savings. Power consumption changes with volume of water pumped to the power of 3. So setting your volume to the minimum you need will reduce your electricity bill.
What is the total running time of a heating pump per year in northern Europe?
(the lower the better)
  1. 2000...3000 hours, if properly controlled
  2. 3000...5000 hours as factory set
  3. 8760 hours, if totally ignored (24h/day)
Given that the kWh costs you about 20 euro cents and the pump eats up 50 watts, you will realize how much your inaction will cost you (point 3).
A heating pump needs to run explicitly for pumping away boiler heat when the burner is running and for a short time after that until the temperatures of inflow and outflow are close. With floor heating you have to add about 2 hours. If parts of the system are not always being switched on and off the pump can remain switched off until the next burner start.
Why does the pump remain running over the whole heating time? It would be possible to reduce running time and current consumption by as much as 80% with no reduction in heating comfort. Are the makers of control systems so extravagant with your money? Actually, it's not too bad: Harald Berewinkel has managed to get his heating pump to run for only 6 minutes after the burner stops!

4.3 The consumer components

At the simplest level, these are pipes (under-floor heating and industrial heating systems) which radiate heat, and all kinds of radiators. Modern radiators are calculated and checked using infra-red cameras in such a way that convection is minimized and a high degree of radiation is ensured (creating the heating comfort you require). If you have a heating system which gives you real comfort, this will be a combination of large heating areas with low flow-temperatures. Why is a tiled stove so pleasant, for example? You should be able to touch the heated surfaces without feeling that they are uncomfortably hot. Your own experience tells you: it is never like that! How can you achieve this?
      There are two ways to achieve comfort at low heating medium temperatures:
Large heating surfaces or low heating losses (or both). Ideally, you should have underfloor or wall heating in a well-insulated house. The increase in building costs only account for a small proportion of the overall costs and have to be paid only once. High heating costs and an uncomfortable atmosphere will bother you permanently.
      Even if the hydraulic balance of your system is correct, individual room control can provide more savings. There are always rooms which heating and foreign sources will make too warm. However, individual room control only makes sense if the temperatures of the heating medium is a lot higher than room temperature. This is because a separate room thermostat is only worthwhile when difference between the temperature of the heating medium and the room temperature is very high.
      With radiators, none of this applies. In this case, thermostatic valves have become standard.

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5. Public buildings: heating with the windows open

If you have seen the figures above, the ones below will shock you. Public buildings are normally managed with no sense of responsibility for economy and the public has no control over what is being spent.
      The figures below are high enough, but what they don't show is the extra heating through electrical current consumed by lighting and other equipment. There is no integrated energy concept.

These are the heating consumption figures for Stuttgart and Hannover:

Type of building Consumption
in L/m per year
Low heating-energy building 3...7 !
Heat conservation regulation 1995 5...10 !
Measured in Stuttgart 1990  
Hospitals 35.3
Homes 25.8
Kindergardens 25.4
Administrative buildings 17.7
Schools 14.5
Measured in Hannover 1993  
Hospitals 51.0
Homes 37.0
Kindergardens 23.0
Administrative buildings 21.0
Schools 19.5
Source: ÖTV Stuttgart
These are the latest figures we could obtain. We can be sure that the situation in hospitals is the same as before.

The bottom line

  • As permanent high-level consumers, hospitals are perfect customers for heating cost surveyors and suppliers of combined heat and power generators, and also in relation to economizing electricity, a financial saving for the public purse.
  • Schools consume at the same level as multi occupied houses.
  • Savings are also administrative buildings because they consume very much in proportion to the amount of time they are occupied.

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page written 1.12.1998, last update 18:23 28.6.2014, Samstag