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Low Loss Headers.

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HHP Ed

On a job at the minute where the boiler manufacturer has specified that there has to be a low loss header installed. Which is fine as got one ready to install. I was just wondering could any of you guys put into plain english exactly what they do and why they are needed as ive never come across one before. The guy im working with tried to explain it but i didnt quite fully understand. So put it in laymans terms please.
 
it does a few things, ive fitted alot and my understanding is:

1 - allows for numerous flow and returns circuits
2 - allows you seperate controls/temps
3 - lets you recirculate return water
4 - has a primary and secondry circuit, can therefore put boilers and primary pumps on first and bring in circuits after, allows you a bit of a back up of heated water
5 - probably other reasons, i cannot remember, maybe somebody will add to this

this of any help?
 
should have added, the ones i worked on were commercial, usually ony needed in larger systems. as they are designed long before i got to site i want involved in that side, just fitted em, we never questioned the design engineers, my knowledge is just from what i worked out for myself, maybe theres more reaons?
 
The low loss header is a bit like a thermal store that other pumped circuits 'dip' into for heat. It's a way of allowing multiple pumps to be fitted. Like one bucket of beer we can all dip our straws into and draw from as and when we need too! That's kind of how I see it anyhoo's :)
 
just googled and it reminded me of an important factor. if you have numerous systems/circuits imagine the pressure/pull through the boiler, If you incorporate a low loss header you can have different velocitys going through the boiler and another through the system, ensuring the water will heat up.

so number 5 - different pressure, which i presume were low loss comes from?
 
Its for a very large house that is being refurbished. 3 large boilers in it 2 doing heating and 1 doing hot water primarys. The guy i was working with said it also helps even up the pressures of the flow and returns to get the best performance out of the boilers. I found this link on them Header basics explained it reasonably well.
 
Ahhh making more and more sense with each post. Clever bit of kit really. Could do the same thing with just making a manifold with very large pipe surely? Although i expect there are a lot of calculations that go into the sizing for the chamber.
 
The last one i saw being installed by the fitters had a CT and VT circuits coming off it , I always think of them as a kind of mixing pool have always enjoyed watching this kind of fit outs come together like a specialist side of fitting .
 
constant and variable temps, not possible without a low loss header

i used to fit them in conjunction with a reverse return system, is that the case here? or is it just 1 boiler?
 
Defo going into the same header the CT circuit going out to batteries and the VT obviously heating ,i installed all the circuit pipework along with couple other fitters and upon nosing in plant room thats what i saw .
 
Just the one boiler here but a couple of cylinders coming off of it. Havent had a detailed look at the system really as im doing the boring part first fixing the heating and bathrooms, would much rather be down in the plant room where i enjoy it much more.
 
gaspastemania said:
Defo going into the same header the CT circuit going out to batteries and the VT obviously heating ,i installed all the circuit pipework along with couple other fitters and upon nosing in plant room thats what i saw .
Click to expand...

wasnt questioning you mate, hope you didnt think that, i was supporting your post
 
fuzzy said:
wasnt questioning you mate, hope you didnt think that, i was supporting your post
Click to expand...

arn't we here to be questioned and advance knowledge ???
you commercial and domestic then fuzzy??
 
Hi there I've put one in on my last job but after I found out that spirotech do one that includes vent, filter etc thought it might be a better idea to have them all in one piece of kit.
 
i was allways told it allows a constant flow rate through the boilers regardless of the system demands
the boiler only sees the flow through the header and the various circuits draw from the header
with large commercial stuf it allows boilers to heat up faster to prevent condensing and possible fractures caused by cold water hitting them direct from the system
 
make sure you follow the manufacturers instructions i have done a few kestons with lost headers and a glow worm set up but the manufacturer stated different set ups .some manufacturers require check valves on the boilers to stop one boiler pumping up the other when its reached temp.keston do some good schematics on their site worth alook - glow worm will email you there set up if you contact them .

ant
 
Can anyone define at which point a system becomes a low loss header? Is there a minimum spec? Ratio? Definition?
 
bengasman said:
Can anyone define at which point a system becomes a low loss header? Is there a minimum spec? Ratio? Definition?
Click to expand...
A system does not "become" a low loss header, it may incorporate one.

The purpose of a low loss header is to hydraulically separate the flow through the boiler from the flow round the rest of the system.


Low Loss Header.JPG
 
maybe the question was meant to read, at which point does a system require a low loss header?

i suppose when the velocity of the water circulating the system is greater than that required by the boiler
 
fuzzy said:
maybe the question was meant to read, at which point does a system require a low loss header?
Click to expand...
Possibly.

I suppose when the velocity of the water circulating the system is greater than that required by the boiler
Click to expand...
Do you mean flow rate? Velocity is related to the diameter of the pipe so 20 litres/minute will have a higher velocity through a 15mm pipe than through a 22mm pipe. It's velocity which determines how many kilowatts a pipe can take as the higher the kW the more litres/min. Trying to send too many kW down a pipe which is too small will require a higher velocity, which means higher friction in the pipe, which means more pressure loss round the circuit, which means a more powerful pump. A high velocity will also produce an unwelcome noise.

Pipes should be sized to give a maximum velocity of 1.5m/sec. See, for example, WB Pipework Sizing Guide, which is based on 1m/sec and Small Bore Heating Systems.

However, I think you are basically correct. If you set the pump so you achieve the correct ΔT at the boiler, the rad at the end of the line does not get hot because the pressure drop in the index circuit is more than the pump can handle.
 
Last edited:
doitmyself said:
If you set the pump so you achieve the correct ΔT at the boiler, the rad at the end of the line does not get hot because the pressure drop in the index circuit is more than the pump can handle.
Click to expand...
Adjusting the pumpspeed to achieve the recommended drop at the boiler is putting the cart before the horse.
The purpose of installing a boiler is to heat up the rads correctly, and therefore the primary goal must be to get the rads at the correct temperature, not the boiler.
 
Last edited by a moderator:
headerimages.jpgWhy should I fit a Low Loss Header?
· 1. Your boiler, particularly the heat exchanger in you boiler, will only function at its peak efficiency when the water velocity passing through it is maintained within prescribed parameters. Boiler manufactures should tell you what the specs are for each make and model. In some cases the flow rate through the system circuit will exceed the recommended maximum flow rate through the boiler, or it may be that the system flow rates are simply unknown. In other cases the reverse is true, where the boiler flow rate exceeds the maximum system flow rate (particularly true in some multi boiler systems). Fitting a Low Loss Header allows the creation of a primary circuit, within which water velocity can be maintained at the required constant, regardless of changes or requirements in the secondary circuits. To sum this up in plain English: The amount of water going around the system (radiators, cylinder etc) might be too much or too little for the boiler.
· 2. Not only is the water velocity important, but also water temperature. There are two potential problems: the first is "thermal shock". If the temp difference between the flow and return is to great, it puts a huge strain; through thermal expansion and contraction, on the heat exchanger. Also the temperature of the water passing through the heat exchanger is important, particularly with condensing boilers, these have their own specific requirements to operate at maximum efficiency. For a boiler to go into "condensing mode" the return temperature should not be higher than about 55'C. So in some cases temperature sensors are fitted on the header to allow control over the primary circuit temperature. Again in plain English: The temperature of the water coming from the system might be too hot or too cold for the boiler.
· 3. Because of the reduced water velocity, the header is an ideal place for positioning an automatic air vent for removing air and a drain point for removing sediment and debris. These are generally fitted as standard on most headers
· 4. The header allows separation of primary and secondary circuits for easier diagnosis when problems occur.
 
Last edited by a moderator:
doitmyself said:
fuzzy said:
maybe the question was meant to read, at which point does a system require a low loss header?
Possibly.


Do you mean flow rate? Velocity is related to the diameter of the pipe so 20 litres/minute will have a higher velocity through a 15mm pipe than through a 22mm pipe. It's velocity which determines how many kilowatts a pipe can take as the higher the kW the more litres/min. Trying to send too many kW down a pipe which is too small will require a higher velocity, which means higher friction in the pipe, which means more pressure loss round the circuit, which means a more powerful pump. A high velocity will also produce an unwelcome noise.

Pipes should be sized to give a maximum velocity of 1.5m/sec. See, for example, WB Pipework Sizing Guide, which is based on 1m/sec and Small Bore Heating Systems.

However, I think you are basically correct. If you set the pump so you achieve the correct ΔT at the boiler, the rad at the end of the line does not get hot because the pressure drop in the index circuit is more than the pump can handle.
Click to expand...

the diameter of the heat exchanger cannot be altered, therefore the only thing that can adversley affect the opportunity to heat the water in a primary circuit is the velocity. At this stage we are not considering the rads, they will be on a seperate pump with a low loss header
Click to expand...
Click to expand...
 
bengasman said:
Can anyone define at which point a system becomes a low loss header? Is there a minimum spec? Ratio? Definition?
Click to expand...

always thought when 2 or more boilers are linked together best to do lost header system .
ant
 
bengasman said:
Adjusting the pump speed to achieve the recommended drop at the boiler is putting the cart before the horse.
The purpose of installing a boiler is to heat up the rads correctly, and therefore the primary goal must be to get the rads at the correct temperature, not the boiler.
Click to expand...
So you adjust the pump to make sure all rads heat up and ignore the temperature drop across the boiler?
 
Hi,

Sorry to bother you. I have a couple of questions

The low loss header goes after the boiler, does a pump need to go between the boiler and low loss header?

Secondly is it best practice to move the pump and zone valves after the low loss header?
Thirdly after the low loss header can you just have one flow with a pump that then splits to the heating and hot water zone valves?
Fourthly can you have a low loss header on a gravity system?

Thanks
 
if theres no pump in the boiler yes, also needs a pump after the llh to the zone valves can be either one size correctly for all load or one for each zone sized correctly

and yes

also yes

and as you would need to change things on the system it would need to be brought upto reds so no gravity (but should work)
 
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