DIY water cooling system for PC: recommendations and step-by-step instructions. Upgrading the CPU Cooling System Additional CPU Cooling

Water cooling systems have been used for many years as a highly efficient means of removing heat from hot computer components.

The quality of cooling directly affects the stability of your computer. With excess heat, the computer begins to freeze and overheated components may fail. High temperatures are harmful to the element base (capacitors, microcircuits, etc.), and overheating of the hard drive can lead to data loss.

As computer performance increases, more efficient cooling systems have to be used. An air cooling system is considered traditional, but air has low thermal conductivity and a large air flow creates a lot of noise. Powerful coolers produce a rather loud roar, although they can still provide acceptable efficiency.

In such conditions, water cooling systems are becoming increasingly popular. The superiority of water cooling over air is explained by the heat capacity (4.183 kJ kg -1 K -1 for water and 1.005 kJ kg -1 K -1 for air) and thermal conductivity (0.6 W/(m K) for water and 0.024-0.031 W/(m K) for air). Therefore, all other things being equal, water cooling systems will always be more efficient than air cooling systems.

On the Internet you can find a lot of materials on ready-made water cooling systems from leading manufacturers and examples of homemade cooling systems (the latter, as a rule, are more efficient).

Water cooling system (WCS) is a cooling system that uses water as a coolant to transfer heat. Unlike air cooling, which transfers heat directly to the air, in a water cooling system, heat is transferred to the water first.

Operating principle of the SVO

Cooling a computer is necessary to remove heat from a heated component (chipset, processor, ...) and dissipate it. A conventional air cooler is equipped with a monolithic radiator that performs both of these functions.

In the SVO, each part performs its own function. The water block removes heat, and the other part dissipates thermal energy. An approximate diagram of the connection of the SVO components can be seen in the diagram below.

Water blocks can be connected to the circuit in parallel or in series. The first option is preferable if there are identical heat sinks. You can combine these options and get a parallel-serial connection, but the most correct would be to connect the water blocks one after the other.

Heat removal occurs according to the following scheme: liquid from the reservoir is supplied to the pump, and then pumped further to the units that cool the PC components.

The reason for this connection is a slight heating of the water after passing through the first water block and effective heat removal from the chipset, GPU, and CPU. The heated liquid enters the radiator and cools there. It then goes back into the tank and a new cycle begins.

According to the design features, the SVO can be divided into two types:

1. The coolant circulates through a pump in the form of a separate mechanical unit.
2. Pumpless systems that use special refrigerants that pass through the liquid and gaseous phases.

Cooling system with pump

The principle of its operation is efficient and simple. Liquid (usually distilled water) passes through the radiators of cooled devices.

All components of the structure are connected to each other by flexible tubes (diameter 6-12 mm). The liquid, passing through the radiator of the processor and other devices, picks up their heat, and then through the tubes enters the heat exchanger radiator, where it cools itself. The system is closed, and the liquid constantly circulates in it.

An example of such a connection can be shown using products from CoolingFlow. It combines the pump with a buffer tank for liquid. The arrows show the movement of cold and hot fluid.

Pumpless liquid cooling

There are liquid cooling systems that do not use a pump. They use the evaporator principle and create a directed pressure that causes the movement of the coolant. Liquids with low boiling points are used as refrigerants. The physics of the ongoing process can be seen in the diagram below.

Initially, the radiator and lines are completely filled with liquid. When the temperature of the processor heatsink rises above a certain value, the liquid turns into steam. The process of turning liquid into vapor absorbs thermal energy and increases cooling efficiency. Hot steam creates pressure. Steam, through a special one-way valve, can exit only in one direction - into the radiator of the heat exchanger-condenser. There, the steam displaces the cold liquid towards the processor heatsink, and, as it cools, turns back into liquid. So the liquid-vapor circulates in a closed pipeline system while the radiator temperature is high. This system turns out to be very compact.

Another version of such a cooling system is possible. For example, for a video card.

A liquid evaporator is built into the radiator of the graphics chip. The heat exchanger is located next to the side wall of the video card. The structure is made of copper alloy. The heat exchanger is cooled by a high-speed (7200 rpm) centrifugal fan.

SVO components

Water cooling systems use a specific set of components, mandatory and optional.

Required components of the SVO:

• radiator,
• fitting,
• water block,
• pump,
• hoses,
• water.

Optional components of the water supply system are: temperature sensors, reservoir, drain valves, pump and fan controllers, secondary water blocks, indicators and meters (flow, temperature, pressure), water mixtures, filters, backplates.

• Let's look at the required components.

Waterblock is a heat exchanger that transfers heat from a heated element (processor, video chip, etc.) to water. It consists of a copper base and a metal cover with a set of fasteners.

The main types of water blocks: processor, for video cards, for the system chip (north bridge). Water blocks for video cards can be of two types: those that cover only the graphics chip (“gpu only”) and those that cover all heating elements – fullcover.

Water block Swiftech MCW60-R(gpu-only):

Waterblock EK Waterblocks EK-FC-5970(Fulcover):

To increase the heat transfer area, a microchannel and microneedle structure is used. Water blocks are made without a complex internal structure if performance is not so critical.

Chipset water block XSPC X2O Delta Chipset:

Radiator. In SVO, a radiator is a water-air heat exchanger that transfers heat from the water in the water block to the air. There are two subtypes of SVO radiators: passive (fanless), active (blown by a fan).

Fanless ones can be found quite rarely (for example, in the Zalman Reserator air conditioner) because this type of radiator has lower efficiency. Such radiators take up a lot of space and are difficult to fit even in a modified case.

Passive radiator Alphacool Cape Cora HF 642:

Active radiators are more common in water cooling systems due to better efficiency. If you use quiet or silent fans, you can achieve quiet or silent operation of the air cooler. These radiators can come in a variety of sizes, but they are generally made as multiples of a 120mm or 140mm fan size.

Radiator Feser X-Changer Triple 120mm Xtreme

SVO radiator behind the computer case:

The pump is an electric pump, responsible for the circulation of water in the water supply system circuit. Pumps can operate on 220 volts or 12 volts. When there were few specialized components for air conditioning systems on sale, aquarium pumps operating on 220 volts were used. This created some difficulties due to the need to turn on the pump synchronously with the computer. For this purpose, a relay was used that turned on the pump automatically when the computer started. Now there are specialized pumps with compact sizes and good performance, operating on 12 volts.

Compact pump Laing DDC-1T

Modern water blocks have a fairly high coefficient of hydraulic resistance, so it is advisable to use specialized pumps, since aquarium pumps will not allow a modern water cooler to operate at full capacity.

Hoses or tubes are also essential components of any water treatment system; water flows through them from one component to another. Mostly PVC hoses are used, sometimes silicone. The size of the hose does not greatly affect overall performance; it is important not to use hoses that are too thin (less than 8 mm).

Fluorescent Feser Tube:

Fittings are special connecting elements for connecting hoses to water supply components (pump, radiator, water blocks). The fittings must be screwed into the threaded hole located on the SVO component. You don't need to screw them in very hard (no wrenches are needed). Tightness is achieved with a rubber sealing ring. The vast majority of components are sold without fittings included. This is done so that the user can select the fittings for the desired hose. The most common types of fittings are compression (with a union nut) and herringbone (fittings are used). Fittings are straight and angled. Fittings also differ in the type of thread. In computer SVOs, threads of the G1/4″ standard are more common, less often G1/8″ or G3/8″.

Computer water cooling:

Herringbone fittings from Bitspower:

Bitspower Compression Fittings:

Water is also an obligatory component of SVO. It is best to refill with distilled water (purified from impurities by distillation). Deionized water is also used, but it has no significant differences from distilled water, it is only produced in a different way. You can use special mixtures or water with various additives. But using tap or bottled water for drinking is not recommended.

Optional components are components without which the SVO can operate reliably and do not affect performance. They make the operation of the SVO more convenient.

The reservoir (expansion tank) is considered an optional component of the water cooling system, although it is present in most water cooling systems. Reservoir systems are more convenient to refill. The volume of water in the reservoir is not important; it does not affect the performance of the water treatment system. There are a variety of tank shapes and they are selected based on ease of installation.

Magicool Tubular Tank:

The drain tap is used to conveniently drain water from the water supply system circuit. It is closed in the normal state, and opens when it is necessary to drain water from the system.

Koolance drain tap:

Sensors, indicators and meters. Quite a lot of different meters, controllers, and sensors for air defense systems are produced. Among them there are electronic sensors for water temperature, pressure and water flow, controllers that coordinate the operation of fans with temperature, water movement indicators, and so on. Pressure and water flow sensors are needed only in systems designed to test components of the water supply system, since this information is simply unimportant for the average user.

Electronic flow sensor from AquaCompute:

Filter. Some water cooling systems are equipped with a filter included in the circuit. It is designed to filter out a variety of small particles that have entered the system (dust, soldering residues, sediment).

Water additives and various mixtures. In addition to water, various additives can be used. Some are designed to protect against corrosion, others to prevent bacteria from growing in the system or discoloring the water. They also produce ready-made mixtures containing water, anti-corrosion additives and dye. There are ready-made mixtures that increase the productivity of the water treatment system, but the increase in productivity from them is possible only insignificantly. You can find liquids for water treatment systems that are not water-based, but use a special dielectric liquid. Such liquid does not conduct electric current and will not cause a short circuit if it leaks onto PC components. Distilled water also does not conduct current, but if it spills and gets on dusty areas of the PC, it can become electrically conductive. There is no need for a dielectric liquid, because a well-tested SVO does not leak and is sufficiently reliable. It is also important to follow the instructions for the additives. There is no need to pour them in excess, this can lead to disastrous consequences.

Green fluorescent dye:

A backplate is a special mounting plate that is needed to relieve the PCB of the motherboard or video card from the force created by the waterblock fastenings, and to reduce the bending of the PCB, reducing the risk of breakage. The backplate is not a mandatory component, but is very common in SVO.

Branded backplate from Watercool:

Secondary water blocks. Sometimes, additional water blocks are installed on low-heating components. These components include: RAM, power transistors, power supply circuits, hard drives and the south bridge. The optionality of such components for a water cooling system is that they do not improve overclocking and do not provide any additional system stability or other noticeable results. This is due to the low heat generation of such elements and the ineffectiveness of using water blocks for them. The positive side of installing such water blocks can only be called the appearance, but the disadvantage is the increase in hydraulic resistance in the circuit and, accordingly, an increase in the cost of the entire system.

Water block for power transistors on the motherboard from EK Waterblocks

In addition to the mandatory and optional components of the CBO, there is also a category of hybrid components. There are components on sale that represent two or more CBO components in one device. Among such devices are known: hybrids of a pump with a processor water block, radiators for air coolers combined with a built-in pump and reservoir. Such components significantly reduce the space they take up and are more convenient to install. But such components are not very suitable for upgrade.

Selecting a water heating system

There are three main types of CBOs: external, internal and built-in. They differ in the location of their main components relative to the computer case (radiator/heat exchanger, reservoir, pump).

External water cooling systems are made in the form of a separate module (“box”), which is connected using hoses to water blocks that are installed on components in the PC case itself. The housing of an external water cooling system almost always includes a radiator with fans, a reservoir, a pump, and, sometimes, a power supply for the pump with sensors. Among external systems, Zalman water cooling systems of the Reserator family are well known. Such systems are installed as a separate module, and their convenience lies in the fact that the user does not need to modify or alter the case of his computer. Their only inconvenience is their size and it becomes more difficult to move the computer even short distances, for example, to another room.

External passive CBO Zalman Reserator:

The built-in cooling system is built into the case and is sold complete with it. This option is the easiest to use, because the entire SVO is already mounted in the housing, and there are no bulky structures outside. The disadvantages of such a system include the high cost and the fact that the old PC case will be useless.

Internal water cooling systems are located entirely inside the PC case. Sometimes, some components of the internal cooling system (mainly the radiator) are installed on the outer surface of the case. The advantage of internal air defense systems is ease of portability. There is no need to drain the liquid during transportation. Also, when installing internal SVOs, the appearance of the case does not suffer, and when modding, the SVO can perfectly decorate the case of your computer.

Overclocked Orange Project:

The disadvantages of internal water cooling systems are that they are difficult to install and require modifications to the chassis in many cases. Also, internal SVO adds several kilograms of weight to your body.

Planning and installation of the SVO

Water cooling, unlike air cooling, requires some planning before installation. After all, liquid cooling imposes some limitations that must be taken into account.

During installation, you should always keep convenience in mind. It is necessary to leave free space so that further work with the SVO and components does not cause difficulties. It is necessary that the water tubes pass freely inside the housing and between the components.

In addition, the flow of liquid should not be limited by anything. As the coolant passes through each water block, it heats up. To reduce this problem, a circuit with parallel coolant paths is being considered. With this approach, the water flow is less stressed, and the water block of each component receives water that is not heated by other components.

The Koolance EXOS-2 kit is well known. It is designed to work with 3/8″ connecting tubing.

When planning the location of your CBO, it is recommended to first draw a simple diagram. Having drawn a plan on paper, we begin the actual assembly and installation. It is necessary to lay out all the parts of the system on the table and approximately measure the required length of the tubes. It is advisable to leave a margin and not cut it too short.

When the preparatory work is done, you can begin installing the water blocks. On the back side of the motherboard behind the processor there is a metal bracket for securing the Koolance cooling head for the processor. This mounting bracket is equipped with a plastic gasket to prevent short circuits with the motherboard.

Then the heatsink attached to the north bridge of the motherboard is removed. The example uses a Biostar 965PT motherboard, in which the chipset is cooled using a passive radiator.

When the chipset heatsink is removed, you need to install the water block fastening elements for the chipset. After installing these elements, the motherboard is placed back into the PC case. Do not forget to remove old thermal paste from the processor and chipset before applying a thin layer of new one.

After this, the water blocks are carefully installed on the processor. Do not press them with force. Using force can damage components.

Then work is done with the video card. It is necessary to remove the existing radiator and replace it with a water block. Once the water blocks are installed, you can connect the tubes and insert the video card into the PCI Express slot.

When all the water blocks are installed, all remaining pipes should be connected. The last one to connect is the tube leading to the external unit of the SVO. Check that the direction of water flow is correct: the cooled liquid must first flow into the processor water block.

After all this work is completed, water is poured into the tank. The tank should only be filled to the level specified in the instructions. Carefully monitor all fasteners and at the slightest sign of leakage, fix the problem immediately.

If everything is assembled correctly and there are no leaks, you need to pump the coolant to remove air bubbles. For the Koolance EXOS-2 system, you need to short-circuit the contacts on the ATX power supply, and supply power to the water pump, without supplying power to the motherboard.

Let the system work in this mode for a while, and you carefully tilt the computer in one direction or the other to get rid of air bubbles. Once all bubbles have escaped, add coolant if necessary. If air bubbles are no longer visible, you can start the system completely. Now you can test the effectiveness of the installed SVO. Although water cooling for PCs is still a rarity for ordinary users, its benefits are undeniable.

Often, after purchasing a computer, the user is faced with such an unpleasant phenomenon as loud noise coming from the cooling fans. The operating system may malfunction due to the processor or video card heating to high temperatures (90°C or more). These are very significant shortcomings, which can be eliminated with the help of an additional water cooling installed on the PC. How to make a system with your own hands?

Liquid cooling, its positive properties and disadvantages

The operating principle of a computer liquid cooling system (LCS) is based on the use of an appropriate coolant. Due to constant circulation, the liquid flows to those components whose temperature conditions need to be controlled and regulated. Then the coolant flows through the hoses into the radiator, where it cools, giving off heat to the air, which is then removed outside the system unit using ventilation.

The liquid, having a higher thermal conductivity compared to air, quickly stabilizes the temperature of hardware resources such as the processor and graphics chip, bringing them to normal. As a result, you can achieve a significant increase in PC performance through system overclocking. In this case, the reliability of the computer components will not be compromised.

When using SZhOK, you can do without fans at all or use low-power, silent models. The computer operation becomes quiet, making the user feel comfortable.

The disadvantages of SJOC include its high cost. Yes, a ready-made liquid cooling system is not a cheap pleasure. But if you wish, you can make and install it yourself. It will take time, but will not cost much.

Classification of cooling water systems

Liquid cooling systems can be:

Types of SZhOK - gallery

When using a serial connection, it is difficult to continuously provide refrigerant to all connected nodes. The parallel connection diagram of the LCC is a simple connection with the ability to easily calculate the characteristics of the cooled units. A system unit with an internal LCC takes up a lot of space inside the computer case and requires high qualifications during installation
When using an external LCS, the internal space of the system unit remains free

Components, tools and materials for assembling SZhOC

Let's select the necessary kit for liquid cooling of the computer's central processor. The composition of the SJOC will include:

All components of the liquid cooling system can be purchased in the online store upon request.

Some components and parts, for example, a water block, radiator, fittings, and tank, can be made independently. However, you will likely have to order turning and milling work. As a result, it may turn out that the SJOC will cost more than if you had purchased it ready-made.

The most acceptable and least expensive option would be to purchase the main components and parts, and then install the system yourself. In this case, it is enough to have a basic set of plumbing tools to perform all the necessary work.

Making a liquid PC cooling system with your own hands - video

Manufacturing, assembly and installation

Let's consider the manufacture of an external pump liquid cooling system for a PC central processor.

Do-it-yourself water block on a computer - video

Water cooling is superior in performance to the air system originally installed on modern computers. Due to the coolant used instead of fans, background noise is reduced. The computer is much quieter. You can make an SJOC with your own hands, while ensuring reliable protection of the main elements and components of the computer (processor, video card, etc.) from overheating.

CPU cooling affects the performance and stability of your computer. But it does not always cope with the load, which is why the system malfunctions. The efficiency of even the most expensive cooling systems can be greatly reduced due to the fault of the user - poor installation of the cooler, old thermal paste, dusty case, etc. To prevent this, it is necessary to improve the quality of cooling.

If the processor overheats due to previously overclocked and/or high loads when operating the PC, then you will have to either change the cooling to a better one or reduce the load.

The main elements that produce the greatest amount of heat are the processor and video card, sometimes it can also be the power supply, chipset and hard drive. In this case, only the first two components are cooled. The heat generation of the remaining components of the computer is insignificant.

If you need a gaming machine, then first of all think about the size of the case - it should be as large as possible. Firstly, the larger the system unit, the more components you can install in it. Secondly, in a large case there is more space, which is why the air inside it heats up more slowly and has time to cool. Also pay special attention to the ventilation of the case - it must have ventilation holes so that hot air does not linger for a long time (an exception can be made if you are going to install water cooling).

Try to monitor the temperature of the processor and video card more often. If the temperature often exceeds the permissible values ​​of 60-70 degrees, especially when the system is idle (when no heavy programs are running), then take active steps to reduce the temperature.

Let's look at several ways to improve the quality of cooling.

Method 1: Correct positioning of the case

The housing for productive devices should be large enough (preferably) and have good ventilation. It is also desirable that it be made of metal. In addition, you need to take into account the location of the system unit, because Certain objects can block air from entering, thereby impairing circulation and increasing the temperature inside.

Apply these tips to the location of the system unit:

Method 2: Clean from dust

Dust particles can impair air circulation, fan and radiator performance. They also retain heat very well, so it is necessary to regularly clean the “insides” of the PC. The frequency of cleaning depends on the individual characteristics of each computer - location, number of ventilation holes (the more ventilation holes there are, the better the cooling quality, but the faster dust accumulates). It is recommended to do cleaning at least once a year.

Cleaning should be done using a soft brush, dry rags and napkins. In special cases, you can use a vacuum cleaner, but only at minimum power. Let's look at step-by-step instructions for cleaning your computer case from dust:

Method 3: Install an additional fan

By using an optional fan that attaches to the vent on the left or rear wall of the case, you can improve air circulation inside the case.

First you need to select a fan. The main thing is to pay attention to whether the characteristics of the case and motherboard allow you to install an additional device. There is no point in giving preference to any manufacturer in this matter, because... This is a fairly cheap and durable computer element that is easy to replace.

If the overall characteristics of the case allow, then you can install two fans at once - one on the back, the other on the front. The first one removes hot air, the second one sucks in cold air.

Method 4: Speed ​​up the fans

In most cases, fan blades rotate at only 80% of their maximum speed. Some “smart” cooling systems are capable of independently adjusting the fan speed - if the temperature is at an acceptable level, then reduce it, if not, then increase it. This function does not always work correctly (and in cheap models it does not exist at all), so the user has to overclock the fan manually.

There is no need to be afraid to overclock the fan too much, because... otherwise, you only risk a slight increase in your computer/laptop's power consumption and noise level. To adjust the speed of rotation of the blades, use the software solution - SpeedFan. The software is completely free, translated into Russian and has a clear interface.

Method 5: replace thermal paste

Replacing thermal paste does not require any serious expenditure in terms of money and time, but it is advisable to exercise some caution here. You also need to take into account one feature with the warranty period. If the device is still under warranty, then it is better to contact the service with a request to change the thermal paste, this should be done for free. If you try to change the paste yourself, your computer will be void of warranty.

When changing it yourself, you need to carefully consider the choice of thermal paste. Give preference to more expensive and high-quality tubes (ideally those that come with a special brush for application). It is desirable that the composition contains compounds of silver and quartz.

Method 6: installing a new cooler

If the cooler does not cope with its task, then it should be replaced with a better and more suitable analogue. The same applies to outdated cooling systems, which due to a long period of operation cannot function normally. It is recommended, if the dimensions of the case allow, to choose a cooler with special copper heat sink pipes.

Use step-by-step instructions for replacing an old cooler with a new one:

And how effective it can be. The need for liquid cooling arose due to the fact that it was decided to overclock the processor, and the faster it runs, the hotter it gets. That is, a standard cooler was no longer enough, and store-bought cooling systems are quite expensive.

Materials and tools for homemade work:
- heat exchanger or water block;
- cooling radiator (from the car);
- pump (centrifugal water pump with a capacity of 600 liters per hour);
- expansion tank (in our case under water);
- four 120 mm fans;
- power supply for the fan;
- various other consumables and tools.

Homemade manufacturing process:

Step one. Making a water block
A water block is necessary in order to remove heat from the processor as efficiently as possible. For such purposes, materials with good thermal conductivity will be needed; the author chose copper. Another option is to use aluminum, but its thermal conductivity is half that of copper, that is, for aluminum it is 230 W/(m*K), and for copper it is 395.4 W/(m*K).

As a result, the water block turned out to be quite large, which affected its weight; when assembled, the motherboard carried a load of 300 grams. And this led to additional costs. To make the design lighter, it was necessary to come up with an additional fastening system for the hoses.

Water exchanger material: copper and brass
The diameter of the fittings is 10 mm
Assembly by soldering with tin-lead solder
The structure is attached to the store cooler with screws; the hoses are additionally secured with clamps
The cost of homemade products at this step is around 100 rubles.

More information about assembling a water block
How the assembly process took place can be seen in the photo. That is, the necessary blanks were cut out of a sheet of copper, tubes were soldered, and then, with the help of a soldering iron, everything was combined into a finished organ of the system.

To reduce noise, the pump should be installed on foam rubber or other similar material. The reservoir was a jar in which the pump was placed. To connect the silicone hoses, metal clamps with screws were needed. To make hoses easier to put on and take off in the future, you can use an odorless lubricant.

Step three. A few words about the radiator
The success of the whole undertaking will depend on how well the radiator works. For the homemade product, the author used a car radiator from a Zhiguli stove of the ninth model; it was bought at a flea market for only 100 rubles. Due to the fact that the distance between the radiator plates turned out to be too small for the coolers to drive air through it, they had to be forced apart.

Test computer:
- Intel Core i7 960 3.2 GHz / 4.3 GHz processor;
- AL-SIL 3 thermal paste;
- power supply OCZ ZX1250W;
- ASUS Rampage 3 formula motherboard.

Software used: Windows 7 x64 SP1, RealTemp 3.69, Prime 95, Cpu-z 1.58.

This material is inspired by impressions from working on a previous article, the hero of which was a silent HTPC in a radiator case. I really wanted to use the AMD A10-5800K in it. A convenient thing that combines a fairly powerful processor and graphics core in one case. But there is one difficulty - its typical heat dissipation is 100 W. At first glance, this is not so much, but the critical temperature of the CPU is 70 degrees. It turns out to be an interesting equation, in which there is a low temperature and decent heat release. Not an easy task.

Naturally, like every reasonable person, I initially decided to take the path of least resistance - buy a commercial cooler that could cope with the task of removing 100 W of heat from the processor.

Cooler options

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The first two are, one might say, veterans, the rest are much younger. Of the entire list, I had the first three, and I decided to try them out in the “passive”, starting with Scythe Ninja.

Naturally, without a fan, since there was little hope for it. Its technical characteristics indicate that it is capable of discharging 65 W in “passive” mode. And I put it on a hundred-watt processor.

The board used in testing was MSI FM2-A85XA-G65. When turned on, monitoring in the BIOS shows 32 degrees, then the temperature begins to rise by about 1 degree per minute and very soon goes beyond 73 degrees. Then I turned it off.