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This instructable documents a simple electrical circuit for saving energy by reducing the stand-by natural gas consumption of a combi boiler. A combi boiler is a device for the supply of residential spatial heating and domestic hot water demand. The main condition for successfully applying this instructable is that in the design of the combi boiler the use of an external switch has been foreseen. Both modern technology combi boilers and older installations might be prepared for it. This instructable proposes a wired solution, a low-tech design without wireless technology.

Financial payback times of half a year or less can be realized at low investment costs. One can expect to need a working time of two hours to two days to do the tests and to install the switches as described in this instructable.

Note that safety restrictions apply and that a few additional conditions must be met (see step 2 in this instructable).

After measuring your own combi boiler stand-by and cold start consumption, and comparing this with your average daily domestic hot water demand pattern, you’ll be able to calculate the benefits of applying the concept from this instructable to your combi boiler. Generally speaking, the smaller your house is, the larger the relative benefits will be. If you don’t use hot water a lot, benefits of omitting stand-by losses will be higher. The higher the natural gas prices you pay (including energy taxes), the more benefit you’ll experience from the energy savings. You may expect net annual savings of $ 7 to 24 per year in the United States, EUR 10 to 36 in the average European Union and EUR 12 to 43 in the Netherlands.

The concept of the circuit described here is made available through a Creative Commons Attribution license (CC BY); the innovative part of the design is explained in step 1 below. For commercial use some directions have been provided in the last section of this instructable (step 8).

Step 1: Introduction

A combi boiler (or combination boiler) is a device for the supply of residential spatial heating and domestic hot water demand, usually run on natural gas and designed for a single dwelling. The part of the system that prepares the domestic hot water can have considerable stand-by losses and consequently significant stand-by energy consumption. I have observed that when such a heating device is being installed in new houses, the manual control (if available) of the hot water preparation system often is not connected. This means that the hot water preparation system is always simply 'on', having hot water available instantly, which results in stand-by losses. Heat is leaking away from the hot water vessel continuously and natural gas is being used at intervals during the whole day, even when no hot water is being tapped. Modern technology combi boilers might be equipped with an 'automatic mode', which might be an energy-saving mode or a self-learning timer-mode. However, I think that more energy reduction is possible when the device is fully controlled manually (this depends on your typical daily use pattern though). Some combi-boilers are equipped with an instantaneous hot water supply system. These might have no stand-by losses, although I expect that some will also be kept at operational temperature, resulting in stand-by losses.

The concept described in this instructable is new and innovate because of three aspects:

1. Using a multiway switching layout allows controlling the combi boiler from two locations in a building, typically the kitchen and the bathroom/shower of a house, or from two different floors. The main advantage is that the combi boiler can be controlled independently from two different rooms, and that the LED provides feedback to the user on the status of the device;

2. The control switch and/or indicator LED is being placed directly at the hot water tap, which is where you need it. Standard installation (if in use at all) usually locates a single switch at the thermostat in the living room. The main advantage of the concept described here is that it is made easier for the user to switch off the hot water when it isn't needed anymore;

3. The complete installation can be performed with simple material like switches, cables and LEDs, available in local stores.

The aim of applying the concept in this instructable is to reduce internal heat losses in the combi boiler and thus to reduce stand-by natural gas consumption.

Combi boilers are very common in Europe. In a recent study by the Energy research Centre of the Netherlands (ECN) an analysis of energy-saving measures has been performed (http://www.ecn.nl/publications/ECN-E--12-013, May 2012, with a summary in English). From this study it can be observed that in the Netherlands the penetration of (condensing) combi boilers is 96% in single and multi-family houses (based on a population of 146 thousand dwellings). This high penetration may be typical for the Netherlands, but it is not for most other European countries. The report also documents the expected average efficiency of the domestic hot water production in a combi boiler, which may vary between 59% and 67,5% (the latter for a condensing type of system, both efficiencies based on the gross calorific value of natural gas). Reasons for these relatively low efficiencies are the stand-by losses and the pipe losses. The concept introduced in this instructable helps to reduce these losses and to increase the overall efficiency.

The realized energy savings will depend on the user demand, i.e. how often hot water is consumed during a typical day. In the next steps I show that significant annual savings per year can be expected if all conditions are met. It is important to measure some characteristics of your combi boiler to estimate the maximum realizable savings. See step 4.

This instructable works for a natural gas-fired condensing combi boiler that is prepared for manual control of the domestic hot water functionality. Apart from safety restrictions (see step 2) also technical conditions apply.  There are two main conditions: the combi boiler must be prepared for an external switch, and you'll need the installation manual of the boiler. The easiest situation is when domestic hot water demand only occurs at two locations in the house (or on two floors). This situation is described in this instructable, using two three-way switches. Installing more switches is possible as well, but this will require a special switch (a four-way or intermediate switch).

As there is quite some information to share, the listing of the required material comes in under step 6 only. In summary: you will need the combi boiler installation manual, two three-way switches, some meters of electrical cable (both with 2 and 3 wires) and two LEDs in the voltage level that you'll determine in step 5 of this instructable, and optionally a casing for integrating LEDs. In step 7 an alternative circuit layout with reduced functionality is introduced, which will be much quicker to install.

Step 2: Conditions Applying to This Instructable

In order to benefit from the concept described in this instructable some conditions need to be satisfied.

Safety conditions:

• If in doubt, consult your local registered installer;
• The installation should not be used by people with vulnerable health (children, elderly people) and you are aware of possible health issues due to the risk of legionella bacteria;
• In case your boiler is used to secure a minimum temperature level of 65 degrees C with a solar water heater connected to the system preferably do not switch off this functionality and don’t install the switches described here because of the risk of legionella bacteria;

Technical conditions:

• A combi boiler is your domestic heating installation;
• You have access to the installation manual (not only the user manual);
• You have access to the gas meter (showing consumption in sufficient detail for measuring purposes);
• You are the owner and/or you are entitled to modify the installation;
• The average daily domestic hot water demand has relatively long intervals
• Possibly you need to drill some holes in a wall and/or a ceiling for the advantage of shorter trajectories and getting rid of cables;

Moreover a basic understanding of electrical circuits is required, as well as understanding the consequences of the manual control (most importantly that for a combi boiler cold start it will take about 1 minute to several minutes before the hot water is available, see also step 3). All users of hot water in the house need to be aware of the new system control in order to avoid annoyance. Be aware that no warranty applies from this instructable. You might damage your system. Be sure to unplug electrical equipment (i.e. the boiler) when working on it.

The next step attempts to make you familiar with the design of a combi boiler and the concept described in this instructable.

Step 3: Understanding Your Combi Boiler

If you know what a combi boiler is than you can safely skip this text.

A (condensing) natural gas combi boiler has two functions: firstly, to heat water for circulating through the radiators in the different rooms in a dwelling, and secondly to supply domestic hot water for use in kitchen and bathroom and/or shower. One of the possible designs of these systems is that a small vessel is integrated into the device, in which the domestic hot water is being kept. Often two operation modes are available:

a) Constantly keeping the vessel at the desired temperature level. This mode is most convenient for the user as domestic hot water is immediately available, but a drawback is the relatively high heat losses, reason for which the boiler is switching on regularly to heat up the water to the desired temperature level (stand-by losses). At night you might hear switching the device on and off (which may as well be caused by a demand for space heating, depending on the room thermostat settings).

b) An 'economy mode' in which the water in the small vessel is only heated to the desired temperature in case actually hot water is being tapped. This mode has no (or fewer) stand-by losses since the water most of the time is being stored at room temperature, at least in situations where long pauses occur between hot water tap moments. The drawback of this mode is the relatively long time it takes to supply water at the desired temperature, as the water in the small vessel needs to be heated first. Some boilers allow to control the temperature level at which the vessel is kept when no heating demand occurs. It might be that manual control still reduces the stand-by losses for those modern combi boilers.

Here comes the important condition. In some boilers an electrical connection is provided for adding an external switch. If the switch is open, heating the hot water storage vessel is switched off. If the switch is closed, heating the vessel is active. Depending on the boiler mode the water is brought to the desired temperature (mode 'a' above) or it is actually being heated once a hot tap water demand occurs (mode 'b' above). It is possible to buy a room thermostat with an integrated switch to control the hot water vessel. A drawback of such a device is that it is usually not installed next to the tap: forgetting to switch on your water heater might force you to go downstairs at the moment you'd like to enter the shower upstairs.

This instructable elaborates on using a multiway switching layout allowing you to control the combi boiler from two locations in the house, typically the kitchen and the bathroom/shower, or from two different floors. The control switch and/or indicator LED is being placed directly at the hot water tap. This is exactly where you need it. The LED shows whether hot water is available (the light is on) or whether you'll have to switch on the domestic hot water functionality and wait a minute. Installing more than two switches is possible as well, but this will require a special switch (a four-way or intermediate switch).

Note: the combi boilers I’ve seen don’t have a pilot light, but electrical ignition instead. I assume that this instructable works for either system, but I am not sure.

The reason for doing all this lies in the expected reduction of stand-by gas consumption for domestic hot water preparation by the combi boiler. However, it is important to measure first the stand-by losses and the cold start natural gas consumption. Then you’ll be able to find out, knowing your typical daily hot water use, whether in your specific case it makes sense to install the manual control switches. This measurement will be discussed in the next step.

Step 4: Measurement and Estimating the Benefits

In order to pronounce on the amount of expected energy saving it is worth performing a measurement test. To do so, monitor the gas consumption on a day when everybody is away or possibly monitor few days after each other to find an average daily stand-by consumption. Make sure that the spatial heating is turned off (don't do this during the winter period if there is a risk of freezing) and that no other appliances use natural gas while all people are out. Doing so, all gas consumption measured can be attributed to the stand-by gas demand of the combi boiler.

For the test it is needed that the gas meter has enough detail to measure relatively small amounts of gas consumption (0.001 m3 is fine). In case the meter has not that much detail, then extend the measuring period.

In this manner I've measured the stand-by consumption of four different combi boilers, which resulted in a daily stand-by consumption varying from 90 to 210 liter natural gas per day, which I extrapolated to 33 to 77 cubic meters (m3) per year. The measurement was done in July 2012 in the Netherlands, with ambient temperatures of approximately 25°C. Note that these values are to be interpreted as maximum achievable savings: a correction is needed for the energy required for heating up the vessel once it cooled down. Be aware that high stand-by losses can also indicate that your combi boiler needs maintenance. For example, fouling in the internal heat exchanger may cause inefficient heat transfer.

In the Netherlands, the average household natural gas consumption ranges from 1250 m3 per year (for apartments) to 3100 m3 per year (for detached houses) (http://statline.cbs.nl/StatWeb/publication/?DM=SLNL&PA=70904ned&D1=56-70&D2=0&D3=6&STB=G1,G2,T&VW=T, July 2012). The abovementioned gross stand-by losses thus represent a share in average household consumption of 1% to 6%.  For the United States the share might be less due to an expected higher average energy consumption per dwelling.

Note that the above calculation implicitly assumes that the stand-by gas consumption is constant during the year. In reality the seasonal changes will result in a month-to-month variation. Two mechanisms might impact the seasonal variation: firstly, during colder periods the temperature level surrounding the boiler may be lower, resulting in a higher temperature difference, higher heat losses to the environment and thus higher stand-by gas consumption. Secondly, in colder periods the spatial heating demand is higher as a result of which the boiler will be in operation more frequently. This means that the internal heat losses of the boiler for spatial heating assist in reducing the heat losses from the hot water storage vessel. In summary, the above extrapolation (resulting in an estimated 33 to 77 m3 stand-by natural gas consumption annually) may not be entirely justifiable and the projected annual stand-by consumption may be smaller or larger.

In Europe, prices for natural gas vary between countries. In the year 2011 the European Union average natural gas price including taxes amounted to 17 EUR/GJ, in the Netherlands this was 20 EUR/GJ (http://epp.eurostat.ec.europa.eu/portal/page/portal/energy/data/database, July 2012). With an assumed energy content of 35 MJ/m3 (gross calorific value) of natural gas, the above mentioned maximum achievable savings would result in annual savings of EUR 19 to 45 in the average European Union, and EUR 23 to 55 in the Netherlands.

In the United States, the residential price for natural gas varies between the states. Assuming an average price of natural gas of $ 11 per thousand cubic feet (http://www.eia.gov/dnav/ng/ng_pri_sum_dcu_nus_a.htm, July 2012, unclear whether taxes are included or not) ($ 0.39  per m3) the projected maximum achievable savings might vary between $13 and 30 per year.

The maximum achievable savings mentioned above can be interpreted as gross savings. If you want to tap hot water after a long period of combi boiler inactivity, and you activate the control switch after the water vessel has cooled down completely, the combi boiler will consume natural gas to heat the vessel up to the desired temperature level. My own measurements of such a combi boiler cold start yielded a natural gas consumption of 20 to 24 liter (average 22 liter). Compared to the above-mentioned stand-by range from 90 to 210 liter natural gas per day this is 24% to 10%. Stated otherwise: in the worst case of this example (210 liter stand-by gas consumption daily and 22 liter gas for a cold start) you’ll reach break-even after 9 times a cold start in a day. In the best case (90 liter stand-by gas consumption daily) you’ll have reached this after 4 times a cold start in a day. In summary: if you have a combi boiler which performs reasonably well, the expected savings might be smaller than anticipated.

In order to translate the cold start issue into monetary terms, it is assumed that on average you’ll make use of the manual control switch twice a day (in the morning and in the evening). The net achievable savings resulting then range from 17 to 61 cubic meters per year, which for the Netherlands would represent a share in average household consumption of 0.5% to 5% (depending on the type of dwelling, see above).  Financially, this results in net annual savings of EUR 10 to 36 in the average European Union, EUR 12 to 43 in the Netherlands and $7 to 24 per year in the United States.

Based on the above estimates, and an expected cost of the material ranging from EUR 10 to EUR 20 (depending on the layout of the house, the materials you have available in the shed and which price level you'd like the new material to have), financial payback times of half a year or less can be realized at low investment costs. Expenses due to time spent in reading this instructable, obtaining the material and preparing and executing the work have not been considered in this calculation. You can expect to need a working time of two hours (best case) to two days (worst case scenario) to do the tests and to install the switches.

It would be great if you could share the results of your own measurements in the comments to this instructable. For easy comparison, state the stand-by gas consumption in m3/year and the anticipated annual savings (in EUR or US $). You could also mention the cold start gas consumption and your combi boiler type.

Summary: after measuring your own combi boiler stand-by and cold start consumption, and comparing this with your average daily domestic hot water demand pattern, you’ll be able to calculate the benefits of applying the concept from this instructable to your combi boiler. Generally speaking, the smaller your house is, the larger the ratio of domestic hot water energy use compared to spatial heating demand will be, and thus the larger the relative benefits will be. If you don’t use hot water a lot, benefits of omitting stand-by losses will be higher. The higher the natural gas prices you pay (including energy taxes), the more benefit you’ll experience from the energy savings. You may expect net annual savings of EUR 10 to 36 in the average European Union, EUR 12 to 43 in the Netherlands and $ 7 to 24 per year in the United States.

In the next step you’ll find out whether the concept described in this instructable will work for your combi boiler.

Step 5: Testing Whether It Works for Your Boiler

To begin first confirm from the boiler manual that your domestic heating device is a combi boiler, which provides both spatial heating and domestic hot water functionality.

Then look in the installation manual of your combi boiler for information on connecting an external interruption switch to control the hot water storage vessel or hot water preparation system. This information can be mentioned in the section that discusses the functionality of the boiler, or you can learn it from the section on the electrical connections. If that doesn’t work, look at the electrical outline of the internal wiring, often displayed at the end of the installation manual. If a connector has been foreseen in the design of the combi boiler it should be mentioned there.

If you must conclude that your combi boiler does not allow installing an external interruption switch this instructable ends here for you. However, there is a listing of alternative measures for improving the boiler efficiency and other energy saving measures in the discussion under step 7 in this instructable. These measures might still be possible in your case. Thank you for joining me until here!

If you find a short-circuited connector pair as indicated on the picture then you might be lucky.

You are now able to test how the boiler behaves when this small cable is removed. Ideally the hot water functionality should then be interrupted. Remember to pull out the electrical plug while working on the boiler, and to take other safety measures when appropriate.

Depending on how often you'd like to switch off the water heating functionality during a day (this depends on your typical daily use pattern) you can decide now which boiler mode is most appropriate for use with the switches. I suggest to put the combi boiler in the 'always on' mode and to have the domestic hot water functionality switched off (using the external switches described in this instructable) during the largest part of the day, provided that your daily domestic hot water demand allows this.

The next step is to perform electrical measurements to find out the voltage level of the required LED. In my case I found a voltage level of 24 V DC, which I already expected as it was indicated in the installation manual of the combi boiler. The electrical current ranged from 0.001 to 0.002 A. If you find higher voltage levels or currents then you really need to pay more attention to safety measures in executing the project.

I also tested whether the LED would light up, and it did. I found out later that also two LEDs light up together.

If you have all this information and the tests show all that the concept works, you can continue to the next steps in this instructable. The following steps are really easy.

Step 6: Connecting Manual Switches in a Multiway Switching Layout

Note: the electrical wiring in the pictures do not match the electrical code: ignore the colors, it is 24 V DC.

As indicated in the introduction, the innovative aspect of this instructable can be found in applying a multiway switching layout allowing to control the combi boiler domestic hot water functionality from two locations in a building, typically the kitchen and the bathroom/shower of a (single family) house or an apartment, or from two different floors. The control switches and/or indicator LEDs are being placed directly at the hot water tap, which is where you need them. Standard installation (if in use at all) usually locates the switch at the thermostat in the living room, which is less convenient and makes it easier to forget to switch the hot water functionality on or off.

You'll need the following material for executing the work:

• Two three-way switches;
• Two LEDs in the voltage level that you determined in the previous step;
• Some meters of electrical cable, with 2 wires from the combi boiler to the first switch, and with 3 wires from the first switch to the second one;
• Optionally you can use separate casings for the LEDs.

For the switches it is convenient if you use watertight ones: firstly because you'll be installing them in wet rooms (installing them like I did horizontally cancels part of the watertight functionality though). But more important is the practical aspect of being able to integrate the LED into the switch casing.

One of the pictures above show the scheme for connecting the multiway switches to the combi boiler. It's really easy.
Connect the switches according to this scheme and connect then the wires to the right connectors on the boiler. In my case the brown cable with two wires is being attached to connectors 4 and 5 as shown in the pictures. This will be different though for every combi boiler. Make sure that the combi boiler is unplugged while connecting the wires.

In order to remember in future what you did when implementing this instructable you can indicate on a piece of paper the function of the cabling, see the pictures. This is especially important in case you are violating the electrical code like I did. You don't want to scare off a skilled professional! Another hint: document the test results, make a print of this instructable and store them close to the combi boiler.

As I wasn't able to find a watertight switch in white color I opted for a conventional switch, and I put the LED in a separate casing, which I mounted close to the hot water tap. Robot (original design by Jeff Fassnacht, https://www.instructables.com/about) informs the user whether the combi boiler is switched on or not by showing the LED. The notice is a bit oversized, but generally speaking it is worth mentioning the function of the LED to the users, and especially in case there is a chance of having visitors. Alternatively you might opt for integrating the LED in a more gracious way in an existing shelf or a cupboard, see the pictures in the next step.

If you have realized the steps above you're done. Congratulations, I hope that you'll see the effect in the bill for natural gas next year. What follows in this instructable is a section with some discussion and further suggestions for reducing energy consumption. After that section, this instructable ends with some words on licensing the concept described.

Step 7: Discussion and Further Suggestions

In case the concept described in this instructable wasn’t compatible with your own combi boiler, or if you’d like to read more on measures for energy saving, the hints below might be useful.

• This instructable might also work for other types of boilers than gas-fired combi boilers. I haven't researched this, feel free to post your suggestions and alternative configurations to this instructable.
• If your boiler is not prepared for manually controlled switching on and off the hot water vessel you might be tempted to switch off the complete boiler. In think that this is not a good idea. A combi boiler usually has not been designed to be booted a few times a day, and besides it might take a relatively long time before the hot water is getting available.
• If you are reluctant to performing all the work with the multiway switches, but your combi boiler does support an external switch, you might decide for an alternative circuit layout and install only one electrical switch, without an LED, but in a place that is easy accessible. Doing so, you’ll have reduced functionality on comfort and user-feedback, but it will be much quicker to install.
• Another hint to save energy is on the side of the spatial heating. If you have a condensing boiler, the temperature difference between the desired water temperature and the condenser (which has a working temperature level of 100°C) influences its efficiency. Instead of running the system on high temperatures (say radiator temperature of 80°C), try lowering the temperature to 50°C. The boiler might be a few percentages more efficient.
• This instructable documents a wired solution, with fixed switches. One could consider using wireless technology for the remote control, but I wouldn't recommend it: it’s much more complicated and the risk is that you don't find the remote control when you need it (I suggest you fix it on the wall next to the hot water tap). One important advantage of a wireless technology though is that you don't need to drill through walls and ceilings, making the installation easier.
• Switching off the boiler while continuing to tap hot water allows rinsing out the hot water and thus reducing the pipe losses of the system. This however yields an increased risk of legionella bacteria exposure, see safety conditions in Step 2.
• High stand-by losses can also indicate that your combi boiler needs maintenance. For example, fouling in the internal heat exchanger may cause inefficient heat transfer.
• Combi boilers usually have a circulation pump for the spatial heating system. Make sure that the pump is not running continuously, but only at times the boiler is working. Note that in order to not damage the pump (through corrosion) it should run for a short while every day. Modern combi boilers do this automatically, but in some cases there is a manual switch for pump options. Check the manual!
• Remotely switching appliances from the electricity outlet can be useful and energy-saving as well in some cases other than controlling a combi boiler. For example, if you have two computers in the house, one downstairs and one in the attic and you're using one LAN switch. Instead of having the switch available 24/7, for energy efficiency reasons you might want to switch off the switch, and a multiple switching layout can prevent you from running up and down the stairs. A 50 Watt device at 8760 hours a year consumes 438 kWh annually. At 0,20 EUR/kWh this is EUR 88 each year. Other appliances to switch off remotely: DECT phones (at times where you don't expect people to call) or even electric hot water boilers (because of the long heating times only if you are away for at least a few days).
• It is also very well possible to have three switches in the system layout, but this will require, besides the two standard switches, a third and special 4-way or intermediate switch.
• If you need a new combi boiler, be sure to obtain information on the average stand-by consumption of the devices available. With the vendor you could discuss whether manual control (like described in this instructable) makes sense, and which types are ready for it.
• If you need a new combi boiler, be sure to opt for condensing technology. It allows capturing heat from the exhaust gas and makes the boiler much more efficient than a non-condensing alternative.

Next step is the final one in this instructable.

Step 8: Licensing and Commercially Using the Concept

The concept described in this instructable is made available through a Creative Commons Attribution license (CC BY, http://creativecommons.org/licenses/by/3.0/deed.en_GB), and the innovative part consists of three aspects:

1. Using a multiway switching layout allows controlling the combi boiler from two locations in a building, typically the kitchen and the bathroom/shower of a house, or from two different floors. The main advantage is that the combi boiler can be controlled independently from two different rooms, and that the LED provides feedback to the user on the status of the device;

2. The control switch and/or indicator LED is being placed directly at the hot water tap, which is where you need it. Standard installation (if in use at all) usually locates a single switch at the thermostat in the living room. The main advantage of the concept described here is that it is made easier for the user to switch off the hot water when it isn't needed anymore;

3. The complete installation can be performed with simple material like switches, cables and LEDs, available in local stores.

The aim of applying the concept in this instructable is to reduce internal heat losses in the combi boiler and to reduce stand-by natural gas consumption.

Commercial use is possible at no costs provided that the name of the author of this instructable, ‘openproducts’ is mentioned. For other arrangements send a Private Message through the instructables member page (https://www.instructables.com/member/openproducts)

Non-commercial use by private home-owners, schools or other utility buildings is encouraged. If you experience real benefits from this instructable then sending a message or posting a comment would be appreciated, or consider to let the author of this instructable share in the gains (for example 10% of the projected or realized net benefit in the first year of stand-by savings). Other suggestions on what to do with your profit: invest in a solar water heater (but read the safety conditions at the start of this instructable once more), in renewable energy in general or other energy-saving measures (like a new condensing boiler if you don’t have one yet). Good luck!

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