Tankless sprinkler systems can save on space and cost for your development. How do you install them safely?
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Do you need a tank for a sprinkler system?
A sprinkler system, in its purest form, does not require a tank. Sprinkler systems simply work like your kitchen tap. The heat from a fire cracks a glass bulb. That bulb is in place to hold back the water held within the system. Once that bulb is broken, the water is set loose and spills out over the fire.
There’s no need for a tank if there’s plenty of water to send out. This can often be the case, with public water supplies in the UK sometimes being known to provide enough water for sprinkler systems.
If the distance by which water can be thrown is dictated by the pressure, the amount of water in the pipes is dictated by the flow. If there’s plenty of pressure and flow, no tank is needed. If there’s not enough pressure: more needs to be provided and this is usually done by a pump. If there’s plenty of pressure but not enough flow, then we need to add water. This is done through a tank. However, the water in the tank can only be sent out by adding pressure.
In a public supply, water stores such as reservoirs are used in place of tanks. These are several miles down the road, but the principle is still the same. Water sits in the reservoir until it is released and sent through the system by a pump. Sometimes, several pumps are needed, with several positioned along the route. These are often referred to as booster pumps.
Pumps used in sprinkler systems are used to add press, so are often booster pumps. It can be seen then, that tanks are not needed. Not all systems need pumps or tanks. Of those that do: pumps can be used without a tank, whereas tanks cannot be used without pumps.
Why use a tankless sprinkler system?
Often, the most challenging part about domestic sprinklers systems is placing the tank. These tanks are not small, with the smallest, full capacity tank in the UK requiring as much water to operate as around 10 baths in the UK.
These tanks need to be placed somewhere, but where that is can often be the issue. Sprinkler tanks are usually tall. Installing short and wide tanks is not an efficient use of space, as can be seen from our article on coffin tanks. However, some properties don’t have the head room (or cash) to install a sprinkler system with a tall tank.
Tankless sprinkler systems can often be seen as the holy grail of sprinkler installation. Tankless sprinkler systems require the minimum amount of space within your property. This can make it easier for occupants and developers to find a home for these systems. It can also increase the resale value of properties which have these systems installed.
How much do tankless sprinkler systems cost?
In many cases, the cost of installing a tankless sprinkler system is no more than fitting a carpet.
Don’t believe me? The price of a decent carpet, with underlay, is typically £40 per m2, plus fitting. A single residential sprinkler can cover up to 25m2, and you should expect to pay between £300 and £200 for each sprinkler head installed. This puts the cost of a sprinkler system at £12 to £8 per m2. A sprinkler system costs roughly a quarter of the cost of the carpet.
In practice, a single sprinkler won’t cover the full 25m2 and so the sprinkler system cost per m2 goes up. The room may be smaller than 25m2. It may be long and thin, which may mean that a single head wouldn’t throw the water far enough. There may be obstructions, or other project specific quirks. Just as the price of a carpet may vary depending on the requirements, the sprinkler system cost varies too.
How does a tankless sprinkler system work?
BS 9251: 2021 defines tankless sprinkler systems. These are simply systems which are fed directly from the public water supply, often referred to as ‘direct feed’ systems. The important thing to know is that while a pump can be installed without a tank, a tank cannot be installed without a pump. We have discussed the ins and outs of sprinkler systems on this site before. Tankless systems work in very much the same way.
Tankless systems rely upon the public mains supply to provide both the needed pressure and flow for the system. This can often work, but it can never be guaranteed.
If flow can be considered as the amount of water flowing through a pipe, pressure should be considered as how far that water can be sent through that pipe. A tankless system would rely upon the public water supply for both of these elements.
Tanks are used to top up the flow of the water. However, if a system has plenty of flow but simply not enough pressure, a tank is not needed. A pump alone can be used to push the water further through the system.
Do sprinkler systems need pumps?
As discussed above: sprinklers do not necessarily need pumps. This is often because the mains supplier (for example: Welsh Water) will have their own pumps situated along the public route.
In a public supply: several pumps are needed, with several positioned along the route. These are often referred to as booster pumps. However, in their purest form: sprinkler systems do not need pumps either. Not when the remaining pressure, which is coming from the public supply, is enough for your system.
Pumps are simply used to push the water through the pipes. If the public water supply is already doing a good enough job of this, having your own pump is redundant. Even so, many home owners feel that this is proportionate to the risk. You may not need a pump, but you may choose to get one in the event that there was ever a problem with the mains supply. This isn’t required, but is an option for additional security.
Do mist systems need tanks?
It’s often the case that residential mist is touted as a tankless sprinkler system option. However, the situation isn’t as simple as that. In fact, it can sometimes be the case that residential mist systems need bigger tanks than sprinkler systems would for the same property.
It’s true that mist systems can sometimes be fed directly from the mains supply, but it isn’t as simple as saying that because the system is mist, it doesn’t need a tank. This is why the residential mist standard includes a specification for mist tanks (see below).
The misconception is becoming more widespread. More and more often, developers are hearing that if they want a tankless sprinkler system, they should look to mist as a solution. So where does this come from?
We’ve identified two sources for the misconception:
- The first is confusion about the difference between system certification and Annex C certification. This is a long topic and addressed more fully in our post on tankless mist systems;
- The similarity between the residential sprinkler standard (BS 9251) and the mist standard (BS 8458). The two are incredibly similar. Surprisingly though, despite the similarities, the two treat fire compartments completely differently.
Sprinklers suppress fires by soaking the fuel. Whereas mist displaces the oxygen and cools the flame. For mist, this creates the benefit of not soaking the surrounding area. An issue which can cause challenges when cleaning up afterwards. However, doing this takes away sprinklers’ biggest benefit.
When a sprinkler system suppresses fire, it soaks the fuel. This is a highly efficient method of operation and allows designers to assume that no more than two heads are operating at any one time. Even if there are half a dozen heads in a room, only two (in a Category 1 system) need to modelled for when considering whether or not a tankless sprinkler system is appropriate.
In contrast, mist systems need to assume that every nozzle within a room (up to 64 square meters) is operating at once. The flow requirements need to support that. The end result is that, when the standard is properly applied: mist is not necessarily the best option for tankless sprinkler systems.
The confusion seems to come from the low flow ability of some mist heads. It seems that, at some point, some designers have confused the two standards and reasoned that: if the heads need less water, then the systems must do too. Unfortunately, that isn’t the case. In practice: mist systems frequently need larger tanks than the equivalent traditional sprinkler systems. This is even more likely if the property is installed across multiple floors.
Do mist systems need pumps?
It’s worth noting that tankless sprinkler systems may still need to use pumps. If there’s plenty of water coming from the mains supply, but it simply isn’t being sent far enough through the pipes, then a booster pump an be installed without a tank.
In many ways: mist systems and sprinkler systems are identical. They take a source water supply, re-route it, and spray it over a fire when triggered. Low pressure mist systems can often be installed without a tank, in the same manner as a tankless sprinkler system.
The two technologies differ when it comes to high pressure mist. These systems leverage the higher pressure to reduce the flow further. To do this, they always need a pump. They may also still need a tank. This is most likely in homes with open plan stairways, or where compartments (rooms) is built across more than one floor. These tanks can sometimes be bigger than sprinkler tanks.
The easiest way to tell if you have been proposed high or low pressure mist is to consider whether hoses are being used or CPVC. CPVC (also referred to as blazemaster, or flameguard) has been checked and approved to make it fire resistant and minimise leaks. However, it can’t withstand the high pressures needed for high pressure mist. Instead, hoses or stainless steel will usually be used, which don’t have the same approvals.
How do you know if your property is suitable for a tankless sprinkler system?
It’s best to assume that a tank will be needed for your system and then work backwards, even if you are able to install a tankless sprinkler system later. Assuming that a tank will be needed ensures that you have enough space in your property as you progress your development. You can then carry out a pressure and flow test to determine if a tankless sprinkler system is an option. If your property is not suited to a tankless sprinkler system, then alternatives can include reduced capacity options.
In practice, it isn’t always straight forward in carrying out these tests. New builds, for example: don’t always have the water connected until the later stages. While the walls and ceilings need to be installed earlier than this. Planning for a full capacity tank and working backwards is the simplest solution.
What if you need a tank?
If you do need a tank, working with your sprinkler installer can ensure that you are provided with the most cost effective, efficient, and viable option.
How big are sprinkler tanks?
If you are concerned that your development may need a sprinkler tank, we have a sprinkler tank calculator which may be of use. The important thing to know is that the size of sprinkler tank needed for your project varies depending on the application. The layout of the building is also important. A taller tank is generally better than a short wide tank, but in practice: the most appropriate tank for your project depends upon the available space. Please see our detailed guide on tank sizing for more information.
Find out more
If you found this post on tankless sprinkler systems useful, feel free to share it and take a look at our other resources over at the Sprinkler Academy for Developers and Regulators.
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