Maximum Flow and Return Pipe Lengths for Log Burner 6M?

[Graham Land]

Help!

Day one after our plumber came to install our new heating system and everything has ground to a halt because of the installation manual.

We had an old coal fired back boiler and oil boiler that met at a neutraliser to heat DHW & rads.

After a cold winter and crazy oil prices we decided we needed to improve the heating system (guessing > 20 years old) and decided to go for a new log burner with back boiler (stratford seb20 eco-boiler) and link it with the oil boiler via a 450 litre thermal store.

The hope is that the log burner will supply most of our requirements.

PROBLEMS :
(1) The log burner is about 8.4M from the thermal store location and the manual says and I quote
"To connect the indirect hot water cylinder use
28mm copper pipes. Ensure that the pipes rise
continuously to the cylinder.
Ensure that runs are not to long, i.e. 6 metres
maximum each for flow and return."

Our plumber is still awaiting a callback from the manufacturer. He wants to find out why this length is vital?
Can anyone enlighten me? The original back boiler ran the same distance with 22mm pipes but was pumped.
Do I really need to consider scrapping the whole boiler project because of this 2.4 M distance?
The pipe run is about 2 metres vertically and then 6.4 metres horizontally.

Yes plumber is qualified, certified etc, but is concerned as manufacturers guides over ride building regs.

Is the manual wrong? Why doesn't their sales literature mention this fact before sales?

Stressed,
Graham

[diamondgas]

Graham you sound 'cheesed off!'

Manufacturers cover their behind and give guidance. Doesn't mean that the installation "can't" be installed, just means they haven't tested their stuff beyond the recommendations or have found issues beyond! Ultimately you are the buyer and your plumber is the installer ... If they think it'll work the shout is yours. The manufacturers however will state recommendations should the fan be coated with excrement!

[Graham Land]

Stressed pregnant wife and two little girls running about the building site (house) wonder why daddy isn't playing...shame on me!!!

[diamondgas]

Kids are the priority, hands down!

[justlead1]

Hi. The length is important as it creates frictional resistance. (Slow circulation) But the vertical height is most important to get good circulation. If the pipe size was increased the length can be extended. But Vertical height still remains the key.

[Graham Land]

If slow circulation is the only concern could I simply get a pump on the return pipe controlled by a pipe stat and have temperature and pressure valve on the flow side?

[justlead1]

Hi. My personal view is no. This is a result of the possibility of a power cut during weather that will induce combustion. Leading to boiling of the water within the system and the associated dangers.

[diamondgas]

If slow circulation is the only concern could I simply get a pump on the return pipe controlled by a pipe stat and have temperature and pressure valve on the flow side?

In one simple word 'yes'. You'll be reluctant, however. to be able to find an engineer to sign his name to it!

We're so constrained ny regs these days that to fart may be a contravention!

Therefore you'll rarely getting anyone here edging beyond what is regulatory!!

[tackleburger]

My feeling on the matter is you go ahead as planned. It will still work but, may take a bit longer for the heat to get there. Get as good a rise as you can and I am sure your plumber knows this but always use pulled bends or 45 deg fittings not elbows.

Pumping is an option but you should use an open vent with the expansion pipe going to outside as like justlead said in the event of a power or pump failure you have no control over the heatsource.

[Graham Land]

Thanks guys for your support it's much appreciated.
Manufacturer was contacted today and explained pretty much what you already stated, they know that 6M works well!

All things steaming ahead now.

@tackleburger - elbows already used due to space constraints of pipe work.

Will be fitting a pump with by-pass loop around it - just in case it needs a little encouragement (due to run length, elbows, etc)

See my next post for which thermal store to buy... I need to know by tomorrow am.

Thank you everyone,
The Worrier

[diamondgas]

Thanks Worrier :-)
Good idea regards pump and bi-pass. On commercial installs the secondary circulation uses a similar set-up. You could fit a gravity non-return valve on the primaries with a pumped bi-pass around it.