Balancing Heating Systems - The Ultimate guide

May 15, 2020

Some heating systems can be an absolute nightmare to balance, no matter how much you fight it you just can't seem to get it all going at once! This guide helps you understand the best way to balance heating systems.

This is usually on larger systems, and many will say that means you probably needed hydraulic separation. However, we have a few tips that we have picked up along the way that will save a TON of time balancing at the end of a job. Making those systems that are impossible to balance, a breeze!!

So What is Balancing Heating Systems?

Balancing heating systems is simply making sure all the radiators or emitters heat up evenly. For systems using weather or load compensation, this ensures you have each room of the property at an accurate temperature rather than some rooms being too hot and some too cold. Too much flow to radiators will overheat rooms, the lower flow will underheat rooms.

With older on/off systems, this would have been more about heat-up times, and potentially less of an issue provided you have TRVs and your reference room (room with the thermostat) is slightly balanced down. This article, like all Heat Geek articles, isn't really about on/off systems though, and more about modern modulating heating systems which should be the standard.

Balancing does NOT increase condensing at the boiler contrary to popular belief. Getting the correct temperature drop across a system is done by controlling the speed of the pump. Unless you have a pump on a high setting and you restrict all of your valves to slow the flow back down, however, this would be exponentially wasteful with pump energy. The key is to not strangle the pump and waste energy. You should always have at least one valve completely open.

Incorrect or lack of balancing does however reduce the output of the system as a whole, this will look like a lower delta T on heat-only boilers where the pumps are not burner linked. More details on our article do balancing increase boiler efficiency?

Why Are Some Heating Systems Such a Pain to Balance?

There are a few key reasons balancing becomes difficult and understanding why is your first step. Here's a quick overview with links to more information.

The first and main reason is that you have high-pressure differentials across the system. This can be due to smaller bore pipework being used, or the fact the system is just large/has a long run. To understand more take a look at 'the relationship of pressure and flow'.

There are two ways we can get around this issue;

We can use one of the many pipework layout methods available to us to minimise the pressure differentials, more information on this is at the bottom of the article, and we can use better balancing valves!

We can't stress this enough, getting the wrong lockshield valves can cause you a complete headache and most are unaware there's any difference!

The other reason may be to do with the balancing method used.

For example, some engineers are trying to achieve a perfect temperature differential (or DT) of 20°c at each radiator. In our opinion, this is unnecessary and difficult.

Another issue is that some engineers put the boiler on full rate when balancing (chimney sweep mode). This will cause the boiler to try and put the maximum boiler output into a system that will most likely only have a radiator output a fraction of the boiler size. This will always lead to a tiny delta t, as the system cannot shift the heat. This will in turn also not have an accurate flow rate when the boiler is put back into normal operation which means you will be balancing for a scenario that will never occur.

Lastly, although they may be good enough in most cases, they might be using completely incorrect valves! Note before we said better valves, however, some lockshield valves aren't designed to balance at all!! Again more here... or there may be a better option described below...

How Would We Advise Balancing a Heating System?

First things first, in order to get the correct flow rate around each emitter/radiator you need to get the correct flow rate going around the whole system. For this, we need to adjust the pump output to suit the system.

A flow rate that’s too slow will mean the property may struggle to get up to temperature at all as the mean (average) temperature of the radiators is too low. If the pump is too fast this will exponentially waste power and also reduce the condensing effect at the boiler by raising the return temperature. Engineers may be tempted to strangle the pump by shutting off valves to slow the flow rate, this again wastes yet more power.

Thankfully, nearly all modern modulating boilers incorporate burner-linked pump control. This continually adjusts the pump speed to give the correct flow rate relative to the heat input. Give a quick check on your heat source to make sure it has the approximate correct DT/flow rate, for more information on refining and setting up your pump speed click here. Don't worry if your DT is 10-20% out, this really doesn't matter too much certainly at this stage, and installers can waste time and get hung up on achieving it.

More about this in our article 'the falsehood of DT20'. However, a more accurate guide is a DT that's around 30% of the flow temperature.

For example; If we have a flow temperature of 70°c (70 x 0.3) gives a DT of 21°c. If your flow temperature is 50°c this would give a DT of 15°c (50 X 0.3) and so on. This is not exact, it's just to get the flow rate in the right ballpark. There are more complex sums you can use but we wouldn't waste time.

Anyway, now your flow rate is in the right ball bark its time to finally balance the radiators.

How to Balance Your Radiators

We can use a few different methods here, importantly none are right or wrong within reason. It's just some methods will take longer than others and some will achieve more accurate room temperatures! We will also assume that we are balancing a modulating boiler with no hydraulic separation.

The two main ways heating engineers balance radiators (if at all) are by either 'feeling the average radiator temperature' and adjusting the lockshield until they feel the same average temperature. At the other end of the spectrum, they use a temperature gauge on each tail of the radiator (flow and return) and balance for a specific temperature drop.

Connecting a thermometer to the radiator's flow and return tails, and adjusting the lockshield valves to give the same temperature drop ensures the flow rates are correct relative to that specific radiator size or output.

However, If you have some temperature drop along the flow pipe before the radiator, this will give you a different 'mean temperature' at each radiator. The mean temperature being the average of the flow and return. To work this out add the flow temp to the return temp and divide by 2.

We don't see a big problem with slightly different mean temperatures, but this will mean you have spent quite a lot of time for something that isn't that accurate anyway as the radiators real-world outputs will vary.

When using modulating controls, we again don't see too much problem with using touch rather than a thermometer provided the room gets to an accurate temperature with any TRVs set to maximum. I.E the flow temperature is targeting the room temperature not the TRV as this could potentially cause the boiler to burn hotter.

As described above, what you could do instead is balanced to give the same 'mean' temperature at each radiator. To do this work out the mean temperature at the heat source (roughly) and adjust each lockshield valve until you have the same mean temperature at each radiator.

Essentially this will give a different DT/temperature drop at all the radiators but your average radiator temperature will be the same. This will work but can again take a lot of time, and will be a pain if your boiler cycles. Importantly this may not give you the perfect balance, after all our target is an accurate room temperature, not an accurate radiator temperature.

Heat loss calculations are not exact, and even if they were they could be thrown out by a multitude of things like missing insulation, calculation errors, how the rooms are used or the incorrect radiator being selected. We think personally both the above options are a bit of a thankless task.

Return Temperature Balancing

What we would instead suggest doing is that after setting your TRV’s to maximum, you simply feel (or measure if you wish) the radiator return temperature while the system is at the 'design flow temperature' (flow temperature required at -2°c approx outside temperature), and making sure the rooms don't get above 20/21°c. At least to start with.

In the vast majority of systems, your flow temperatures to each radiator will be broadly the same, there's not much point in measuring them at all. Touching the radiator to feel the average temperature also leaves only a small margin for error. Measuring the return temperature, however, has by far the biggest margin for error.

To elaborate, assuming a boiler with DT 20 ish, a radiator return that's 8°c out will have a mean temperature that's only 4°c out.

example of radiator temperature depending on different return temperature for balancing heating systems
Fig 1

Whereas if we were feeling the average radiator temperature and we made the same 8°c error we would have hugely different DT's, and in turn massively varying flow rates through each emitter.

For example.

example of radiator temperatures depending on delta T
Fig 2

Because measuring the return temperature is a bigger variable, many systems may be close enough by simply feeling the return pipe with your hand. For more accuracy, though you can use a thermometer of some description or a combination of the two, this is the first point in which you'll vastly increase your balancing speed and accuracy.

Accuracy does not have to be perfect right now, go around getting all your return temperatures to approximately match.

On larger systems, you may find that you have had to restrict the nearer radiators so much that you need to increase the pump speed. This is because the pressure differential across the flow and return is much greater on larger systems in order to get a high enough flow rate. More information on this in understanding pressure and flow.

Go back to the pump and measure your DT at the heat source and approximately adjust the pump output if needed but this is unlikely on most systems.

Again, you do not need exactly matching return temperatures. The radiator sizing will never be exact as the radiator will have been upsized or downsized to the nearest radiator, also - rooms share heat.

Now, this shouldn't have taken a lot of time at all. You could now either ask the occupant to keep an eye on room temperatures and if one is a little high you can balance down slightly later or show them. If a room is a little low in temperature increase the flow rate (reduce the DT) to increase that radiator output though this is unlikely to occur though in our experience.

We realise that most systems still use on/off control instead of modulating controls like weather compensation or room compensation. For this we would advise targeting the return temperature roughly, balancing down your reference room (room with the thermostat in) to a slightly wider DT, and then letting TRVs do their thing. Alternatively use the automatic balancing valves offered by IMI, Honeywell or Danfoss.

If You Are a Stickler for Accuracy However, You Can Take This to the Next Level…

Shut all the internal and external doors, windows and curtains (to prevent solar gain) in the property and set the modulating control to target the highest temperature you are comfortable working in.

You will then need to measure each room temperature individually and adjust the lockshield to make each room the exact same temperature. Go to each room and tweak each lockshield if required, open up the lockshield valve very slightly if the room is cooler than your target temperature and close it down if the room is too warm.

This is a much better use of your time than making each radiator have the same DT, as mentioned it's the room temperature we’re targeting, not our radiator temperature.

Be aware of other variables such as solar gain when doing this. Also note, the wider the difference between inside and outside the more accurate this method will be, this can be achieved by either waiting for a colder day or turning up the modulating thermostat higher, or both. This last adjustment will more likely just show you how forgiving your system is and that the property shares much of its heat.

After your balancing is complete and you are happy with your heating curve (if required) you can set your TRV's back to limit internal gains.

Quick tip. If you are balancing towel radiators (towel rail valves are very quick opening), close down both sides not just one. By closing down one side then the other you will have more rotation on the valve for less flow change, effectively meaning you improve the opening characteristic.

As mentioned, this suggestion for balancing makes the assumption that you are balancing a modern modulating boiler only. It will work for all other system types too, but there are other options available if your modulating boiler is not controlling the flow rate around your system.

Before reading the next section it would be useful to understand the pressure and flow!

What Type of Pump Are You Trying to Balance?

If you have an older boiler, no modulating controls, or Hydraulic separation on your system, other methods of balancing are also available. OR you might not even need to use lockshield valves to balance!

In the commercial world, for example, it's imperative to know how you are going to control each circuit. You will then choose a pump control type in combination with a valve type that compliments it, to efficiently distribute flow.

Pumps use different methods to manage the flow and save energy. You could have burner linked, DT controlled, differential pressure control, outside sensor control, constant pressure, constant speed, proportional pressure and more (an article to follow on these).

But typically this can be broken down into 2 groups, pumps that vary the speed to target pressure, and pumps that vary the pressure to target a speed. You would then select a specific valve type that works to supplement this.

The problem with domestic modern modulating boilers is that they vary both the pressure AND flow rate. This can be very complicated to manage, and so the only option left is to balance with the humble lockshield, which is more than ample in domestic we might add. However, all lockshields aren't the same for balancing! What you didn't know about lockshield valves!

Grunfos Alpha2 System

The Grundfos Alpha2 system will work with any of these pump logic or any valve. However, you have to use their Alpha 3 pump.

Once the system is filled and cleared of air, you connect an external Bluetooth module to your phone and the pump. Your phone will then instruct you how much to adjust the lockshield or what presetting flow-limiting TRVs should be adjusted to. After finishing this will then generate a report showing that you have balanced which may be handy for the imminent balancing legislation.

Automatic balancing valves

For pumps that target a fixed pressure and vary the flow, I would recommend flow-limiting TRV's, or automatic balancing TRV's.

Automatic balancing valves aka pressure independent control (PIC) are usually commercial valves that have a built-in flow limiter, and these are simply TRV versions of those. They incorporate a flow rate selector underneath the TRV head and is numbered say 1 to 5. Each number corresponds to a flow rate which will be in the manufacturer's instructions, simply select the flow rate you require and adjust! GREAT!

We would strongly advise setting the pump carefully with these. If the pump targets a set pressure differential across the valve is below 1meters head they don't have full control and the further radiators may struggle. However, these valves typically have quite small-bore restrictive pathways (and increased valve authority), so this will be unlikely. Take note though, if you run the pump at a higher differential pressure than the minimum required, your pump power consumption will increase.

For example, if you can get enough flow to the radiators with 3 meters head, but the pump is left at 6m head, you will double your power consumption. You should absolutely experiment with lowering your pump speed until flow begins to suffer. If you double your resistance, you double your power consumption this is a direct linear relationship. Read more

If your pump is targeting speed, you will need to be even more careful. If the set speed is even slightly above your total flow limit through all the valves added together, then the valves will place exponentially more resistance against the pump, and the pump will increase to maximum pressure differential to compensate. This will draw the maximum power, for that flow rate. It's for this reason, we would always suggest leaving one bypass radiator for any excess flow to go through when using these valves.

We would not suggest these valves for use with a modern modulating boiler that varies both pressures and flows for the reasons described above, or with a DT-controlled pump. Here's a little explainer.

Automatic balancing trvs

You also have available PIC (pressure independent control) valves that work in line with the pipework, however, this would only be expected to be used with larger commercial systems.

The only other advice we would give when it comes to valve selection is to be aware of and understand valve authority and valve 'opening characteristics'. This is fully covered in our 'what you didn't know about lockshield's' article.

The other variable to whether you require extra time balancing or different valve types depends on how your system is piped and may be easier to resolve by adjusting when you replace the boiler or installing in a slightly different way from the start. System layout also dictates what pump setting you should ideally use.

System Layout

Installing or adjusting pipework in a slightly different way when installing a new boiler can ensure that balancing is easy, and even negate the need to balance the system at all!

As described in Understanding pressure and flow, when you balance a heating system you are effectively making each circuit have the same or similar resistance as each other. The main reason systems are out of balance and have dissimilar resistance is because of the communal pipework. That is the common pipework they all share.

The nearer radiators (or shorter circuits) will use less communal pipework and so have less resistance to flow than the radiators further down the line. So water takes the path of least resistance.

pump head distribution though a basic heating system diagram

There are two ways to address this. The first is to make the communal pipework large. Ensuring larger communal pipework means that the majority of the resistance is within the individual legs of the pipe and the pressure differentials end up much closer 'out of the box and even before you have balanced. Unlike the picture above.

This also increases your system's valve authority as more of the relative pressure loss is at the valve.. a win-win!

Many may talk about the dangers of low velocity. This has never been a concern for us on domestic systems, and your pipework will be oversized 99% of the year anyway as the system modulates (we hope). Another article to follow up on this another time.

The second way is to keep the communal pipework short.

Manifold Systems

Manifold systems refer to where you run your flow and return to a manifold. Similar to an underfloor manifold, or perhaps one you have created yourself. This can be located anywhere in the property but ideally centrally, then split off for individual runs to each radiator or emitter.

manifold heating system by Dave Chorley
Installation from Dave Chorley Plumbing and heating

This ensures all the radiators have similar communal pipework resistances, and if/when an emitter turns off, the pressure effects on each of the other emitters is the same/similar.

A manifold system makes it so easy to balance (if necessary at all) as it’s all in one easily accessible point.

Reverse Return System

First in last out, is the term generally used in the trade. This is the same as a traditional 2 pipe system, however, the first radiator your flow pipe feeds is the last radiator in your return circuit. This has the effect of making all your radiator circuits similar resistances.

reverse return heating circuit diagram

You may find this impractical, however, there are as many versions of all of these techniques as your imagination will allow.

For example, rather than running your flow and returning to the first radiator, then sequentially to the second etc. You could run your flow and return past the first rad to the centre of the property then tee out like a spider diagram. Then again tee out from there keeping the primary pipework larger.

The more you can create equal resistances like this the more a constant pressure mode will suit. A proportional pressure setting would be better selected for undersized and poorly planned systems. More on this another time

None of this is essential knowledge, however, once you have understood the theory this will help with the decision-making process later so you can decide on the fly. And as mentioned a few times now, all this can really be more helpful for larger systems.

This may be one of the last pieces of content we will be publishing here for a while as we push harder on our online video course that's currently under development.

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    May 15, 2020
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