New boiler with old FULL Gravity system.

[chrisbeney]

I have a full truly all-gravity system: 2 1/2 inch iron flow pipe, cast iron radiators, no pump, no electrics whatever, no hot water (currently separate electric system for that). Apx 100,000BTU/hour, 45kW Ideal gas boiler. Works fine. Goes to attic with 2 1/2 inch pipe and then branches down to first, then ground floor, via four somewhat narrower pipes.

Would like to install modern (probably condensing) boiler. I don't want to have new rads or pipes.
Does anyone have experience with using such a boiler in such a system?

I imaging the larger water volume in the pipe system will possibly slow the flow and may reduce the heat to the ground floor rads.
Might it affect the flow and return temperatures and would that have adverse affects?

Does a true gravity system have a greater water flow or a lesser flow than a normal pumped condensing system?

Any issues that I haven't thought of?

Chris

 

[doitall]

First you have to identify the flow, not guess.

On a ladder system the return is the bigger pipe returning to the boiler after the smaller flow pipes have connected into it.

Having decided which is the flow, (and it is important to get it right) then you can connect to them with reducers in the normal way.

The existing cold feed and vent should be connected to the old boiler, these will need to be connected before the pump as a standard fully pumped system.

Watch out for open vents at high level, possibly existing the roof, these will need to be removed and auto air vents fitted.

The pipe size will not be a problem on an open vented system, and I wouldn't advise a sealed system.

If you have or get any problems you can always email me (in my profile)

 

[kevplumb]

jeez glad i'm only a young un

 

[doitall]

jeez glad i'm only a young un

I thought at Interbuild you were catching up fast

 

[Strachan]

That would have been a good one for water systems to get his teeth into! I miss him No news yet from admin Kev?

 

[kevplumb]

nope yer old git you where listening sharpish DJ

 

[kevplumb]

That would have been a good one for water systems to get his teeth into! I miss him No news yet from admin Kev?

do you think he would want to play wiv the big boys marra

 

[chrisbeney]

Thanks 'doitall', that is an encouraging reply.

Flow pipe is known, there are two returns, one into each bottom side of the existing boiler, would need linking into one of course.

Cold feed goes to one of the return pipes just before the boiler, so could probably stay there.
Vent pipe comes off the 2 1/2 inch flow pipe at its highest point in the attic by the feed tank, rises some ten foot and would discharge into that tank which is some five foot above the flow pipe. I suppose it depends on the pump head as to whether that is satisfactory or if a new overflow pipe is needed the whole house height.

Have you practical experience of this sort of installation?

Chris Beney

 

[doitall]

What I think you are saying is the flow rises to the loft with a branch for the ground floor, which connects to the rads and drops back to the boiler seperately to the top floor.

Is the 1st floor the same e.g. a branch off before the pipe gets to the loft.

The conventional way would be, if you picture a ladder, the left rail being the flow and the right rail being the return, with the rungs being the connecting link between the radiators.

Practical experience

Ok so you're system may be a tad smaller than what I'm used to 2,000,000 btus + or - a few 0000s

perhaps a quick sketch would be in order.

 

[chrisbeney]

No, the flow rises to the loft with no branching on the way at all. In the loft it runs nearly horizontally with four downward branches. Each branch goes down to under the ground floor, passing a rad on first and on ground floors (except in one case where the first floor one is omitted). These downpipes pass at one side of the cast-iron rads (except for the single one) and are connected to the rads top and bottom with swept tees or in the case of the single rad fed in one side and out other side bottom. The four pipes are merged under the ground floor to two, which return to the boiler.

Definately not a ladder type system.

Chris Beney