What diameter of gas hose to choose according to the appliance type
Why the diameter of a gas hose is more important than it seems at first glance
When a customer comes to the store or writes a query about a gas connection hose, they usually focus on only one thing - the length. They need to connect a stove, boiler, or flow water heater and are looking for a piece of hose that physically reaches from the shut-off valve to the appliance. The diameter of the hose, i.e., its internal diameter (marked as DN), is rarely considered - and this is one of the most common causes of complaints, insufficient appliance performance, or, in the worst case, problems with the tightness of the connection after a few months of operation.
The diameter of the hose directly determines how much gas the hose can transfer per unit of time at a given pressure drop. If you choose a hose with too small a diameter for a powerful appliance, so-called flow restriction occurs - the appliance does not receive enough gas, the burner does not burn at full power, the boiler does not reach its rated output, and in the extreme case, the low-pressure safety switch may activate. On the other hand, an oversized hose with a larger diameter than necessary for a small appliance is not dangerous, but it is unnecessarily expensive and less flexible when handling.
In this article, we will look at how the hose diameter relates to the appliance's performance, what diameters are actually used in practice for different types of appliances (stove, oven, boiler, flow heater, grill, infrared heater), and how to correctly verify what diameter your specific appliance requires. If you are also dealing with the question of length, I recommend supplementing your information with the article What length of gas hose is suitable for your appliance - diameter and length influence each other when selecting.
Basic terms: DN, inch marking and the difference between internal and external diameter
Before we get to the specific recommendations, it is necessary to clarify the terminology that is commonly used in catalogs and on hose packaging and that often confuses a layperson.
Nominal diameter DN
DN (Diamètre Nominal, nominal diameter) is an approximate value of the internal diameter of a pipe or hose in millimeters. In household gas connection hoses, you will most often encounter DN 8, DN 10, and DN 13. This is an approximate marking - the actual internal diameter may vary slightly according to the manufacturer and the hose construction (stainless steel corrugated hose vs. rubber hose has a different wall structure).
Inch and metric thread marking
A separate chapter is the thread by which the hose is connected to the shut-off valve and the appliance. The most common are G1/2" threads (internal thread diameter approx. 15 mm, roughly corresponds to DN 15), G3/8" (corresponds to DN 10), and G3/4" (DN 20) for more powerful appliances. It is important not to confuse the thread diameter with the internal flow diameter inside the hose - the hose may have G1/2" threads on both ends, but the internal flow diameter of the corrugated part itself may be smaller, for example DN 10 or DN 13. This internal diameter determines the flow capacity, not the size of the thread.
A detailed analysis of when to use internal and when to use external thread on each end of the hose can be found in a separate article Internal thread vs. external thread - differences and use. For common household appliances (stoves, ovens, smaller boilers), the most common in practice has proven to be the internal-internal thread, which you will find, for example, in these length variants directly in our range: Gas hose internal - internal 500 mm, Gas hose internal - internal 1000 mm or Gas hose internal - internal 1500 mm.
Section diagram of the hose - where exactly we measure the diameter
The diagram above illustrates the principle of measurement - the external diameter includes the braiding and protective layer (corrugation in stainless steel hoses), while DN (internal diameter) represents the actual flow cross-section through which the gas flows. When selecting a hose according to the appliance's performance, we always work with the DN value, not the external diameter.
How the hose diameter relates to the appliance's performance
The amount of gas that a hose can transfer depends on three main factors: internal diameter (DN), hose length, and pressure drop (difference in pressure before and after the hose). Physically, flow capacity increases approximately with the square of the diameter, while pressure loss increases with the length of the hose and decreases with the fourth power of the diameter. This means that even a small increase in diameter significantly improves flow capacity, while extending the hose length at the same diameter reduces flow capacity.
In practice, this has a simple consequence: the more powerful the appliance (the more kW it needs for full performance), the larger the hose diameter it requires - and it also applies that with a greater distance of the appliance from the shut-off valve, we should choose a larger diameter rather than a too long thin hose (more on this in the article about hose length).
Approximate graph - flow capacity according to diameter
The graph illustrates the principle, not precise engineering values (which vary according to the type of gas, pressure in the network, and the standard according to which the hose was certified) - it is important to understand the trend: as the diameter increases, the capacity of the hose increases significantly faster than one might expect from a linear ratio of diameters.
Recommended diameters according to appliance type
The following overview is based on common installation practice when connecting household and smaller commercial gas appliances to natural gas and propane (LPG). However, the decisive factor is always the manufacturer's data in the manual or on the type plate of the appliance - the following values serve as an approximate guide and to verify the correctness of the selection, not as a substitute for the documentation of a specific appliance.
Gas stoves and cookers (individual burners)
A standard four-burner stove usually has a total power of between 8 and 12 kW. For such an appliance, a hose with a diameter of DN 10 is sufficient, connected via a G1/2" thread. In practice, we also encounter DN 8 for stoves without an oven or for separate stove tops, but due to the minimal price difference between DN 8 and DN 10, I always recommend choosing DN 10 - it has a reserve for the possibility of replacing it with a more powerful appliance in the future.
Gas stoves with oven (combined appliance)
If the stove includes a gas oven for baking, the total power of the appliance typically ranges between 12 and 18 kW (four burners plus an oven with a power of 2 - 3 kW). In this case, it is appropriate to choose a hose with a diameter of DN 10 to DN 13, depending on the total power sum indicated on the appliance's label. With newer stoves with an oven and a grilling burner, it is advisable to opt for DN 13 to avoid pressure drops even when all burners and the oven are turned on simultaneously.
Flow water heaters (so-called "gamatky")
Flow water heaters belong to the most power-demanding household appliances - their power usually ranges from 17 to 24 kW, and even higher in larger models. For this type of appliance, DN 13 is standard, and in some cases (especially at greater distances from the shut-off valve or in older supply systems with lower available pressure), a DN 16 diameter with a G3/4" thread is recommended. An insufficient hose diameter in flow water heaters typically results in water temperature fluctuations or incomplete burner ignition when hot water is drawn from multiple locations simultaneously.
Wall-mounted and stationary gas boilers
Common domestic condensing and classic boilers have a power range of 18 to 35 kW. For this category, DN 13 is standard, and for more powerful boilers over 30 kW or in cascade configurations with multiple boilers, it is recommended to switch to DN 16 or directly connect using rigid piping instead of a flexible hose (which is common practice in stationary installations according to inspection standards). With boilers, it is also important to consider that the boiler manufacturer usually specifies the minimum hose diameter precisely in the installation instructions - this value must be respected in preference to general recommendations.
Gas grills, cooking stoves and larger garden appliances
Garden gas grills with one or two burners typically have a power of 8 to 15 kW and can be sufficient with a DN 10 or DN 13 hose, depending on the distance to the pressure cylinder or regulator. For larger cooking stoves, catering equipment or high-power grilling units with power over 20 kW, it is advisable to consult the manufacturer directly regarding the diameter - these appliances often require a DN 16 or larger diameter, or even rigid steel piping instead of a flexible hose.
Infrared heaters and direct heating gas stoves
Infrared heaters (for example in workshops, halls or verandas) typically have a power of 3 to 13 kW per unit. A single infrared heater can be sufficient with DN 8 to DN 10, but when multiple units are connected to a common branch, it is necessary to calculate the total power of all appliances on that branch and choose the diameter of the main supply accordingly (not necessarily the diameter of the individual connecting hose to each appliance).
Overview table - appliance power and recommended diameter
| Type of appliance | Typical power | Recommended DN diameter | Common thread |
|---|---|---|---|
| Cooking hob / stove without oven | 8 - 12 kW | DN 8 - DN 10 | G1/2" |
| Stove with oven | 12 - 18 kW | DN 10 - DN 13 | G1/2" |
| Flow water heater | 17 - 24 kW | DN 13 - DN 16 | G1/2" - G3/4" |
| Wall-mounted / stationary boiler | 18 - 35 kW | DN 13 - DN 16 | G1/2" - G3/4" |
| Garden grill | 8 - 15 kW | DN 10 - DN 13 | G1/2" |
| Infrared heater (1 unit) | 3 - 13 kW | DN 8 - DN 10 | G1/2" |
| Catering appliance / cooking boiler | Over 20 kW | DN 16 and more | G3/4" and more |
Consider this table as an orientation aid for quick checking - it is always necessary to compare the values with the appliance label or installation instructions. During kitchen renovations or when replacing an old stove with a more powerful model, it often happens in practice that the original hose has a diameter that was sufficient for the older appliance with lower power, but is now undersized for the new model.
Relationship between diameter and length - why it matters where the hose leads
In practice, the diameter and length of the hose are always assessed together. The longer the connecting hose, the greater the pressure drop along its length - and this drop is significantly more pronounced with a small diameter. This means that if you need to cover a greater distance (for example, a boiler located further from the riser, or a stove on an island in the kitchen distant from the wall with the shut-off valve), it is better to choose a length that you actually need and rather increase the diameter, than stretch a thin hose to the maximum allowed length.
In our range, you will find hoses with internal threads on both ends in lengths 500 mm, 750 mm, 1000 mm, 1250 mm and 1500 mm - when choosing a specific length, we recommend measuring the actual distance from the shut-off valve to the appliance connection with a small reserve (about 10 - 15 %) for natural hose bending, not stretching it to the maximum in a straight line.
Connection diagram - from the supply to the appliance
As shown in the diagram, the hose is only one link in the chain between the main supply and the appliance. At each connection (shut-off valve - hose, hose - appliance), it is important to pay attention to the correct type of thread, which we discuss in more detail in the article "Internal thread vs. external thread - differences and use", and on the correct tightening according to the procedure described in the article "Installation of a gas connecting hose step by step."
Practical examples from service practice
Over the years of installations and service interventions, we repeatedly encounter several typical scenarios that clearly illustrate why the hose diameter is important.
Example 1: Replacing an old stove with a new one with an oven and grill
The customer had an original two-burner stove without an oven connected with a DN 8 hose. After replacing it with a new four-burner stove with an oven and a grilling burner (total power 16 kW), the original hose was left in place. The result was a noticeable flame drop on the burners when the oven and two burners were turned on simultaneously - a classic sign of an undersized diameter. The solution was to replace it with a DN 13 hose.
Example 2: Flow water heater at the end of a long run
During the renovation of an apartment block, the flow water heater was moved further from its original connection point, requiring a longer connecting run. Instead of increasing the length while keeping the original DN 10 diameter, we recommended switching to DN 13 with an appropriate length - this helped the customer avoid pressure issues when the heater and another appliance were simultaneously drawing power from the same branch.
Example 3: Garden grill with a long hose to the gas cylinder
A common mistake with garden grills - the customer uses a thin hose of 1500 mm instead of a shorter one with a larger diameter, because they want the cylinder to be "out of sight" further away from the grill. With a higher grill power (over 12 kW), this causes slower burner ignition and uneven burning, especially at low outdoor temperatures, when the pressure in the LPG cylinder naturally drops.
Common mistakes when choosing the hose diameter
- Coping the original diameter without verifying the new appliance. When replacing an appliance with a more powerful model, it is always necessary to check the power rating on the label, not automatically use the old hose.
- Mixing up the thread size with the flow channel diameter. A hose may have a G1/2" thread on both ends, but the internal diameter may be only DN 8 - it is always necessary to look at the declared DN value, not just the type of thread.
- Stretching a thin hose to maximum length instead of increasing the diameter. For longer runs, it is more appropriate to choose a larger diameter rather than maximizing the length with a small diameter.
- Ignoring the total power when connecting multiple appliances on one branch. When connecting multiple appliances (e.g., two infrared heaters), the diameter of the main branch must be calculated based on the total power, not just the power of one device.
- Underestimating the manufacturer's recommendation for the appliance. The installation instructions for a boiler or flow heater almost always specify the minimum hose diameter - this value takes precedence over general tables.
How to proceed when choosing - step by step
The practical procedure for choosing is as follows: first, determine the power of the appliance from the factory label or manual (usually in kW), then verify the type and size of the thread on the side of the shut-off valve and on the side of the appliance (more in the article about internal and external threads), measure the actual distance of the route, choose the DN diameter according to the table above, and finally choose a specific length from the range and install the hose according to the step-by-step guide in the article "Installation of a gas connection hose step by step". After installation, it is always necessary to perform a tightness test - the procedure can be found in the article "How to check the tightness of a gas connection."
Material of the hose and its influence on the choice of diameter
Along with the diameter, the material of the hose also plays a role - a stainless steel corrugated hose usually has a slightly different flow cross-section compared to a rubber (rubberized) hose with a textile reinforcement at the same outer diameter, because the wall construction is different. Stainless steel hoses are generally more resistant to mechanical damage, rodents, and UV radiation, which is advantageous especially for appliances installed outdoors or in areas with a higher risk of damage (boiler rooms, technical rooms, garden kitchens). A detailed comparison of both types can be found in the article "Comparison of stainless steel and rubber gas hoses - for the same type of appliance, the recommended DN diameter does not change essentially, only the construction and durability of the hose change."
When it is advisable to consult a specialist
Despite tables and general recommendations, there are situations where it is advisable to consult an experienced gas technician or service technician: when connecting multiple appliances to a common branch, in catering businesses and larger commercial appliances over 30 kW, when the route length is non-standard and exceeds the standard hose dimensions, or when combining natural gas and LPG within one installation (as the flow parameters differ slightly due to the different density and calorific value of the gas). In such cases, we recommend having a professional design prepared or at least verifying the choice of diameter directly with the appliance manufacturer.
Lifespan of the hose and its relation to the diameter
The hose diameter itself does not significantly affect its lifespan - this depends mainly on the material, mechanical stress, and environmental conditions (temperature, humidity, UV radiation). Nevertheless, it is advisable to check during each appliance replacement or regular inspection of the gas installation whether the currently installed hose corresponds to the current requirements for diameter and its overall condition. More about when it is time to replace the hose regardless of the diameter can be found in the article "Lifespan and replacement of gas hoses - when it is time for service."
Frequently asked questions about gas hose diameters
Can I use a hose with a smaller diameter than recommended by the appliance manufacturer?
This is not advisable. A smaller diameter will limit gas flow, the appliance will not reach its rated power, and in some cases, it may cause unstable flame combustion or problems with ignition. Always follow the minimum diameter specified in the appliance installation manual.
Is there a problem with using a larger diameter than necessary?
No, using a larger diameter is not a safety issue - the hose will simply carry more gas than the appliance needs, which does not interfere with it. The only disadvantage is a slightly higher price and somewhat reduced flexibility of the thicker hose when handling in tight spaces.
How do I determine the diameter of the currently installed hose?
The DN diameter should be printed or engraved directly on the hose body or on the end fitting. If the marking is missing or unreadable, we recommend measuring the inner diameter of the fitting opening with a caliper when replacing, or consulting the seller according to the type and power of the appliance.
Do the same diameters apply for natural gas and propane-butane (LPG)?
The recommendations in the table are applicable for both types of gas, as the hose itself does not distinguish between gases - the appliance power in kW is the determining factor. However, it should be noted that with LPG from a pressure cylinder, the inlet pressure may be lower especially at low temperatures, so for higher powers (over 12 - 15 kW), it is advisable to choose a larger diameter from the recommended options.
Must the hose diameter be the same as the diameter of the fixed pipe distribution?
Not necessarily. The connecting hose is only a short flexible section between the shut-off valve and the appliance, its diameter is chosen according to the power of the specific appliance, not according to the diameter of the entire home distribution system, which is usually adapted to the total power of all appliances in the building.
What if my appliance has a thread that does not match the available hose diameters?
In such a case, there are reducing fittings (adapters) that allow you to connect a hose with a different thread diameter, but the internal diameter of the hose should still match the recommended DN according to the appliance power - reducing the thread does not solve any possible underdimensioning of the flow cross-section.
Summary
The diameter of the gas connecting hose is not a detail that can be estimated - it directly affects whether the appliance achieves its rated power and whether it will operate reliably even when multiple burners or appliances are in operation simultaneously. For common household appliances (cooking hobs, stoves), you can manage with a diameter of DN 8 to DN 10, while for more powerful devices such as flow heaters and boilers, DN 13 is standard, and DN 16 for higher powers or longer routes. It is always most reliable to follow the data in the specific appliance manual and, in case of doubts, choose a larger diameter rather than rely on an estimate. When selecting a specific hose in our range, do not forget to combine the correct diameter with the correct length - both criteria complement each other and together form the basis of a safe and functional gas appliance connection.
Do you have a question on this topic?
Having trouble making a decision or dealing with a specific situation in your home? Write to us - we'll be happy to help.