What is better double-circuit or single-circuit gas boiler: features of the device and operation

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Oleg Zubarev
Last update: August 2019

Choose a gas boiler for arranging an autonomous heating system in a private house or apartment? Agree, I want to choose the best equipment that can provide you and your family with hot water and heat in the cold season. But you can’t decide what is best to buy - a double-circuit or single-circuit gas boiler?

We will help you understand this issue - the article discusses the features of dual-circuit and single-circuit equipment, their main advantages and disadvantages, the subtleties of using each of them. A comparison of two types of boilers was also performed, thematic photos and video recommendations were selected for choosing the best option, based on the individual needs of a potential buyer.

Device and features of operation of boilers

Modern gas boilers, depending on the number of circuits, can be single-circuit and double-circuit. They are externally and structurally similar, but are designed to solve different problems, and in different conditions.

As a result, it can be argued that both types of equipment are equally useful and efficient, so there is no better one among them. So it all depends on the right choice. Next, we will examine in detail how the single-circuit type of a gas boiler differs from its double-circuit analogue.

Differences in the design of single and dual circuit units

Products that belong to both types of equipment for the most part consist of the same components.

The detailed design of a modern single-circuit wall-mounted boiler and the circuit diagram of its double-circuit “brother” are shown in the following figures:

Single circuit gas boiler
Any single-circuit boiler is structurally simple. What makes them more reliable and affordable. But the listed advantages are offset by the need to buy a boiler
The device of a double-circuit gas boiler
The presence of a complex heat exchanger and a three-way valve in a double-circuit unit makes it fundamentally different from any single-circuit analog

The main components of the two types of boilers are similar - both the name and purpose.

So, similar elements of single- and dual-circuit equipment:

  • cold water supply pipelines;
  • gas-burner;
  • membrane tank;

Even a structural element designed for heating water is called the same - a heat exchanger.

But, if you look at it, it turns out: the name is the only thing that this assembly is similar in for boilers of different types — the heat exchanger of a single-circuit unit is a pipe that serves to efficiently transfer heat released during gas combustion to water.

Double circuit gas boiler
An important difference between double-circuit boilers is that they are equipped with everything necessary for space heating and hot water supply. Therefore, there will be no additional costs for the purchase of equipment, and they also save space

And in the case of its dual-circuit analogue, everything is not so simple, since its heat exchanger is structurally more complicated. Moreover, such products are divided into separate subspecies and there are bithermic and dual.

In the first case, the design is a pipe placed in a similar product with a larger diameter. This feature allows you to create 2 circuits, one of which is designed to transfer heat to the liquid used for heating, and the second for the hot water system.

The dual heat exchanger consists of:

  • pipesthat provide heating water for heating;
  • platestransmitting heat to liquids for water supply.

That is, the heat exchangers of double-circuit boilers differ in structural complexity solely because of the need to solve 2 problems.

But still, the most significant difference between single-circuit and double-circuit products is the presence of the latter three way valve. Which task is to change the direction of hot water.

So in the standard position, the valve is in a position in which the coolant is supplied only to the radiators. Everything changes when the hot water tap opens. Since the three-way valve, having received the corresponding signal, moves to a different position. Namely, in providing the supply of hot water.

At the same time, the coolant supply to the radiators is stopped, and in full - the premises will not be heated throughout the entire time that hot water is used for domestic purposes.

That is, the design of the double-circuit boiler allows it to supply hot water in only one of two modes. But still, this feature should not be considered a weak point of equipment.

Comparative review of gas boilers

Both types of equipment are used to heat the coolant in order to heat the premises, buildings. And on this the functionality of single-circuit boilers is limited.

Modern floor gas boiler in the boiler room
A single-circuit gas boiler is used exclusively for heating the coolant entering the radiators of the heating system. But if we add an indirect heating boiler to it, then it, like its dual-circuit analogue, will be able to provide hot water supply

Their dual-circuit analogues are additionally used to provide hot water supply in order to solve any domestic problems. That is, they give the opportunity to take a shower, perform any other hygiene procedures, wash dishes, etc.

Next, we will conduct a comparative review of single and double circuit boilers according to a number of criteria.

Comparison criteria Single-circuit boiler Double-circuit boiler
type of instalationfloor; wallfloor; wall
absent if there is no need for
DHW if DHW is required, then you need to purchase a cumulative
absent if there are no more than 2 sampling points and they are located next to the boiler
Cost-effectivenessturns on when the water temperature in the boiler cools below acceptable
the heating circuit turns on when the coolant is cooled below an acceptable level;
DHW circuit is switched on every time after the start of water withdrawal
Compactnesswhen used in conjunction with
the occupied area actually doubles with a boiler
more compact single-circuit; wall-mounted models are suitable for use in confined spaces
The convenience of usewhen used together with a boiler
hot water will be the same temperature at all points of selection; coolant is evenly supplied to the heating system
when there is insufficient boiler power and many points of water intake, differences are possible
water and heat carrier temperatures
more abrupt; with open taps, water is not supplied to the heating system

As you can see, for the organization of hot water supply in the presence of a single-circuit boiler, you will have to additionally buy equipment. For example, indirect heating boiler. And this is an additional expense.

Moreover, after buying a boiler, it will have to be installed and connected correctly. And how to do it right and what to consider when operating such devices, we described in detail in this article.

Advantages and disadvantages of equipment

Both types of gas boilers are easy to operate, efficient and durable. And they have an attractive appearance.

The design of each type of gas boiler is designed to meet the needs of various categories of users, which clearly demonstrate their advantages and disadvantages. And they also provide an opportunity to understand the differences between a single-circuit gas boiler and its double-circuit analogue, helping a potential buyer to make the right choice.

Pros and cons of single-circuit units

Such products are able to provide stable heating of rooms of any area, number of storeys, remoteness from the heat exchanger.

And, in addition, single-circuit boilers:

  • more reliablethan their dual-circuit counterparts, the design of which is more complex, which leads to a slightly larger number of breakdowns;
  • easier to maintain, which is also caused by design features;
  • cheaper.

An important advantage is that single-circuit units can become the basis for connecting other equipment. That will expand their functionality and increase the comfort of living.

You should always remember that if you need to provide hot water in the premises, you will have to buy a storage boiler along with a single-circuit boiler. And this will lead to considerable additional costs. And a set of the listed equipment will take up a lot of space, which can be critical for small apartments

Single circuit gas boiler
Connection of storage boilers will provide premises with hot water supply. Moreover, water at any time will be supplied hot, which is not always possible to achieve from dual-circuit analogues

In this kind of equipment, in the absence of the need for hot water supply, there are no pronounced shortcomings. But otherwise, the lack of universality immediately affects. Which leads to the need to purchase an additional electric heating device.

As a result, its joint operation with a single-circuit boiler leads to:

  • high cost for purchase, installation, maintenance;
  • limited water for domestic needs - for sharing with single-circuit units, boilers are most often bought, so the question may arise about the rational consumption of water, the volume of which depends on the capacity of the drive;
  • greater wiring load.

The last drawback is relevant in cases where the old wiring is used in the house or apartment or powerful electrical equipment is used in parallel.So, you may need to upgrade the wiring and cable selection larger section.

You should also be aware that a set of single-circuit boiler and boiler takes significantly more spacethan one double-circuit boiler. And with limited space, this can be a significant drawback.

Advantages and disadvantages of double-circuit boilers

Units that belong to the specified type with some limitations, but are still able to provide two systems at once with hot water (heating, hot water supply). And they also take up less space than their counterparts with boilers. As a result, double-circuit boilers are more convenient to use.

Features of gas boilers
Both types of gas boilers are easy to operate, efficient and durable. They also have an attractive appearance.

In addition, the competition between manufacturers has led to the fact that the difference in the cost of both types of units is gradually leveled.

Therefore, today you can find a double-circuit boiler whose price slightly exceeds the same indicator of a single-circuit product. Which in some cases can also be considered an advantage.

If we talk about the disadvantages of double-circuit boilers, the most important is the inability to instantly provide hot water of the same temperature to all water consumption points in a house or apartment.

So, in their heat exchangers the amount of water that is needed right now is heated. That is, stock is not created. As a result, the temperature of the water may differ from expected or change during its use. This happens when the pressure, pressure changes, for example, after opening / closing the second valve.

Wall mounted gas boiler
When using a double-circuit boiler, the water temperature often differs at two different points of water intake - hot water can be delivered to the desired point with a delay, and significant. Which is inconvenient and leads to additional costs.

As for the installation, then installation of double-circuit boilers - This is a more complicated procedure, especially at the design stage. Since you will have to comply with numerous manufacturer recommendations

Which boiler is better to choose?

When choosing the best boiler, it should be borne in mind that each type of equipment is designed for specific conditions. Subject to which they will show maximum efficiency, they will achieve the expected result and mitigate the shortcomings.

Therefore, it is so important to determine your requirements and take into account living conditions. So, if the equipment is selected in an apartment and there is no extra space for installation, then the ideal option would be double-circuit wall boiler. And although it is inferior in power to outdoor models, it is quite capable of satisfying the needs of residents.

For a summer house or a private house, where there is a separate room for equipping a boiler room, a wonderful solution is to install a floor-mounted single-circuit boiler for gas in conjunction with a boiler of the required volume. That will provide for the needs of the family in hot water and heat.

Installation of a single-circuit boiler
When installing any model of a floor single-circuit boiler with a boiler, an order of magnitude more space is required than for double-circuit analogs. And the load on the equipment in this case will be higher, so it is important to choose the right boiler capacity

If you select a heating unit for a suburban two-story house or cottage, then in this situation it is best to stop at a powerful double-circuit floor boiler with integrated large volume heater.

Floor gas boilers with one and two circuits differ more power from their wall-mounted "brothers." They are also most often non-volatile. This is quite convenient, especially if there are power outages in the region.

More recommendations and important selection criteria for gas boilers we have given in next article.

Conclusions and useful video on the topic

This video will help to understand the features of various varieties of gas boilers:

The video is intended to deepen knowledge on the topic and help make the right choice:

When choosing between a dual-circuit boiler and its single-circuit analogue, one should not ask about what is better. Since all of the specified equipment is modern, productive and durable, but, as mentioned above, is designed to solve various problems. Therefore, it is so important to take into account personal needs and living conditions so that the equipment does not disappoint you.

And how many circuits does your gas boiler have? Share your impressions of the use of your heating equipment - tell us, does your chosen boiler meet all your needs or for some reason do you consider your choice wrong? Add a photo of your gas boiler, indicate its pros and cons found during operation.

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