The Use of manifolds in Domestic Heating Systems

What are heating manifolds and why you should use them?

Most of you are aware of Manifolds, particularly from Underfloor Heating applications. This article is addressing the increasing use of them in traditional wall hung radiator systems, with the advent of plastic piping.

Manifolds are revolutionising installations in the same way that computer cabling did in the IT industry some years ago. They allow you to move away from the traditional ‘ring’ circuit system to a ‘star pattern’ system, giving significant advantages in the speed of installing a system, and commissioning it.

star plumbing circuit

ring plumbing circuit

Key differences between a traditional ‘ring’ system and a ‘star’ system are as follows:

A manifold based ‘star’ system can improve installation time by up to 40% (dependant on your choice of pipe). How? You eliminate up to 75% or more of all joints. There is little or no requirement for tees and elbows (depending on the radius of curvature of the particular pipe you choose, please refer to BS7291 pipe manufacturers data in each case).
The cost saving in not using these fittings is then offset against the increased metreage of pipe required, and the manifold cost itself.
The remaining joints are limited to the wall hung radiators and the manifold, reducing inaccessible joints and minimising leak potential.
In the eventually of a leak, if you have chosen a manifold with isolation facility, it is easy to isolate just the circuit that is leaking, leaving the rest of the system free to continue functioning.
Manifolds give you central control. Depending on the functionality you require, you can provide the following functions from the one location: Filling, draining, isolation, hydraulic balancing, flow and temperature control. All of these reduce the installation, commissioning and maintenance time on site.
Manifolds should be fitted as part of the first fix, allowing them to play a key role in pressure testing. You can isolate at this point, and pressure test the installed pipework.
Heating manifolds provide independent flow and return circuits to each radiator, making control of the energy requirement per radiator that much easier. Hydraulic balancing between circuits is easier, and can also be done on the manifold with an integrated flow meter.
Centrally located manifolds significantly improve the speed at which the last radiator on the traditional flow ‘ring’ circuit receives its hot water. This avoids the old problem of one radiator producing heat well before another.

What types of manifold are there?

There are many, from simple plastic manifolds to sophisticated weather compensating manifolds. Here we have addressed the standard solutions available in the UK market.

This can be split into two groups:

By construction there are brass and plastic manifold. Plastic is generally a simple tube with multiple branches, brass is generally flow and return rails mounted on an offset bracket. Co-planar (or bi-polar) manifolds will be discussed later.
By function there are three types: –
Type 1 – Manifold supplying wall hung radiators, with Thermostatic Radiator valves (TRV’s) and lockshields on the radiator.
Type 2 – Manifolds supplying wall hung radiators, no longer using a TRV, but instead using a pair of Wheelheads or Lockshields on the radiator. It uses a wall thermostat instead of a TRV, wired back to the manifold, which has an electrothermic head on the return rail.
Type 3 – Manifolds as per type 2, supplying underfloor heating circuits, but incorporating a secondary pump and a temperature controller.

What heating manifold is best suited for your application or installation?

The selection of your heating manifold should be based on the following issues: Where can I locate it? What functionality do I want from it?

We will address location in a later a paragraph. Functionality is linked to whole life costing analysis – the choice should reflect installation and commissioning time, cost of the relative systems, the energy efficiency requirements (Part L of the Building Regulations) and maintenance intervals linked to the workload (the longevity of the system).

Type 1 manifolds
These are the simplest and increasingly used on new housebuild. As a minimum, you need a flow and return rail. It is common to add simple functionality like manual or automatic air vents, and a pair of ball valve isolators (red and blue handled). Further functionality can be added:

Drain and fill points can be added to each rail, making it easy to fill the system for commissioning, and maintenance.
Isolators per circuit help with filling and commissioning. You may wish to carry out your hydraulic balancing here, and so the addition of double regulating lockshields is necessary. These can incorporate flow meters.
An integral differential pressure by-pass valve (as per Good Practice Guide 302) can be added.
To measure your flow and return temperatures, you can use flow and return ball valves incorporating thermometers.

Type 2 heating manifolds
These can have all of the additional functionality described above, but now with the addition of electrothermic heads on the return rail.

These allow you to use a programmable or simple room thermostat, per room. This form of individual room zoning, particularly using a programmable room thermostat with time and two levels of temperature control (comfort and energy saving) increases the energy efficiency of a heating system significantly, allowing easier compliance with Part L of the Building Regulations (Conservation of fuel and power) and Best Practice (GPG 301, 302 and GIL 59 CHeSS).

You will also need a wiring box, to signal the pump and boiler when circuits are closed. It also eliminates the need for a 2-port motorized valve and its accompanying wall thermostat.

Type 3 heating manifold
For underfloor heating, you can use a type 2 manifold, but with the addition of a secondary pump (for the longer pipe runs) and a temperature controller (for the reduced running temperatures).

Where to locate a heating manifold?

They should be as centrally located as possible, with easy access. They can be located in stud walls, inside a plastic or metal cabinet. Other common locations are in the airing cupboard (first floor) or under the stairs (ground floor). If these are not central enough, then locate them in the ground floor roof space, between joists (using a co-planar manifold). Typically, you use one per floor, between 6 and 8-ways.

Where within a heating system should they be installed?

Following Building reguWhat are heating manifolds and why you should use them?

Why use a bi-polar or co-planar manifold?

This type of manifold is a single piece design, with flow and return connections cross linking through the opposite rail, without mixing the water. These have a smaller ‘footprint’ then conventional manifolds, in depth and height, and can be fitted horizontally. They are commonly used in roof spaces, between joists.

Can I use the same manifolds for both wall hung radiator (WHR) systems and underfloor heating systems (UFH)?

This question can occur when you are looking at UFH on the ground floor, and WHR on the first floor. The only difference is the requirement in a UFH system for a secondary pump and a temperature controller. These are often separate items or a separate kit to the manifold. However, we offer an all in one solution, the Floor Mixing Unit.

A Type 2 manifold, with electrothermic heads on the return rail is identical in both cases. If you wish to fit a manifold on the UFH circuits with an integrated pump and temperature controller, choose a type 3 manifold. If you don’t wish to have individual room zoning, relying on TRV’s then use a type 1 manifold for the WHR part of the system.

Mixed Systems

What can I do if I have an Underfloor heating (UFH) manifold system but also have some wall hung radiators (WHR) on the same floor?

Manifolds make addressing this issue easy. Simply use a manifold system that allows high temperature flow and return rails on the same manifold set, before the secondary UFH pump and temperature controller. This means you use one central manifold control set, rather than two, reducing installation time and costs. You also retain the central control functions you have chosen. Emmeti offer the Floor Mixing Unit, which allows these high temperature circuits to be added.

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