New boiler - re-use old gas pipe?

[fumb]

With gas prices climbing higher than Edmund Hillary I think the time has come for an upgrade to a new efficient boiler.

At the moment I'm in the cogitation/planning stages before looking for installers.

The current Crane Cavalier boiler, a cast iron floor standing behemoth, is sited approx dead center of the downstairs space on an inside wall of the kitchen. It is flued into an existing internal chimney breast so reusing the old flue is a non starter unless I've misunderstood something. I would also prefer to move it out of the kitchen to reclaim some space.

Originally I was thinking loft install but a quick measure suggests a 60+' external run of probably 30+mm pipe would be required. Not to mention boarding the loft, handrails, lighting etc etc to create a safe working place for the installer. All in quite a lot of additional expenditure to put the boiler somewhere that doesn't strike me as a great place for it.

So now I'm wondering if upstairs wouldn't be a better choice than the loft. The current hot water tank is up there almost directly above the current boiler (gravity how water setup) in an airing cupboard with loads of room for a boiler and access to an external wall via an extant cupboard. All it would need is is a few feet extension of the gas pipe to get it upstairs

Which brings me to the question. Downstairs is all parquet over solid concrete. The existing gas meter is at the far end of an attached garage probably 30' from the boiler as the crow flies. From the meter a 1 1/2" cast looking pipe dives into the concrete and emerges by the boiler. There's also a gas cooker outlet a couple of feet further along.That's all I know about the pipe and inspection is going to be impossible.
Assuming the pressure tight and drop under load numbers all check out would you use the extant pipe given that it's some sort of iron (not galvanized silver in appearance) buried in concrete?

 

[oldbuffer]

1. It is usually mild steel pipe.
2. Almost certainly imperial sized. Where:
2.1 3/4" bore = 26.5 mm outside diameter (OD). OR
2.2 1" bore = 33.5 mm OD
3. Likely to branch under the floor, usually with the diameter from the meter extending to the boiler and one size smaller going to the hob.
4. Measure the outside diameter of the pipe (not any fittings) coming out of the floor to the boiler. If its 1" bore pipe you'll almost certainly be OK. If its 3/4" bore it will probably be OK but might be marginal.
5. It will be up to the gas safe installers to determine suitability. There is nothing wrong in re-using steel pipe, provided there are no leaks, provided it has the requires gas carrying capacity.

 

[Harry Bloomfield]

So now I'm wondering if upstairs wouldn't be a better choice than the loft. The current hot water tank is up there almost directly above the current boiler (gravity how water setup) in an airing cupboard with loads of room for a boiler and access to an external wall via an extant cupboard. All it would need is is a few feet extension of the gas pipe to get it upstairs

If you swap your setup to combi, then almost certainly a combi would need a new larger gas supply from meter to boiler. The existing size might allow for a heat only boiler, but there is the issue of 'gravity hot water setup' - did you mean you have a large tank in the loft and a hot water cylinder, maybe in an airing cupboard? If the latter, and it is viable, then it is probably worth hanging on to that layout.

 

[gas112]

crane cavalier from the 60`s so good chance your pipework to rads is a one pipe system not the most efficient . cylinder will be on gravity as well .
You have a major upgrade on your hands not just a straight forward boiler change

 

[fumb]

Many thanks for the replies folks

Harry,
I have an unusual hot water system. It was a standard loft tank with cylinder setup providing gravity fed hot water. It's now plumbed as a heat bank providing mains pressure hot water with only a f&e tank in the loft.
It still relies on gravity circulation from boiler to tank
I would like to keep the heatbank setup (I have vague plans for solar in the future) although I'm aware it will need to be converted to a fully pumped s or y plan with a heat only boiler.


Gas112, it's a two pipe setup thankfully, beautifully piped in 15mm stainless for the visible runs downstairs

Oldbuffer,
I've never noticed before. What goes into the floor in the garage is 35mm or 1 3/8” outside dia. What comes out in the kitchen is 1" and thinking about it there's a (probably) gas poker connection in the lounge which had already been connected to a gas fire when I bought the house

I'm getting the feeling that the only way to know if the existing pipe is suitable will be to test it and see. Is this something that can be assessed by an installer in advance of the boiler install or does it need the new boiler to provide the full load? I'd really like to know in advance while I'm in the planning stage

 

[Harry Bloomfield]

I've never noticed before. What goes into the floor in the garage is 35mm or 1 3/8” outside dia. What comes out in the kitchen is 1" and thinking about it there's a (probably) gas poker connection in the lounge which had already been connected to a gas fire when I bought the house

You might be able to trace the route of the pipe, with a metal detector, to find where the pipe T's to fire and boiler. Knowing the route, and pipe lengths/sizes, it should be possible to then work out whether the existing pipework is adequate. The final test comes once the boiler is fitted.

 

[fixitflav]

What goes into the floor in the garage is 35mm or 1 3/8” outside dia. What comes out in the kitchen is 1"

Sounds like 1" nominal bore in the garage. Do you mean same in the kitchen, or is that 1" OD? Even if it's 3/4"NB, unless the boiler is unusually high output there should be no problem of pressure drop. Might be borderline if you go for a combi, but you haven't mentioned it, and that's another reason not to go that route, you obviously don't want to dig up the floor.

I would like to keep the heatbank setup (I have vague plans for solar in the future) although I'm aware it will need to be converted to a fully pumped s or y plan with a heat only boiler.

Well worth converting to fully-pumped, but why go for S or Y-plan? You might want to have weather compensation, which needs different boiler flow temperature setpoints for CH and HW, usually with HW preference. To achieve that with S-plan needs an additional relay, and with a mid-position valve (Y-plan) needs setting up so the mid position is inactive. That's a more expensive, less reliable valve, and not using its full functionality. W-plan with an either/or valve gets round it.

 

[Harry Bloomfield]

To achieve that with S-plan needs an additional relay, and with a mid-position valve (Y-plan) needs setting up so the mid position is inactive.

The control system will take care of not using the mid-position, mine does.

 

[fixitflav]

The control system will take care of not using the mid-position, mine does.

That's right, if you already have Y-plan and want to add weather compensation. But if starting from scratch an either/or valve is cheaper and more reliable, and the control system probably simpler. Problems with mid-position valves come up on here regularly.

 

[Harry Bloomfield]

Problems with mid-position valves come up on here regularly.

Yep, the spring return versions.

 

[fumb]

Yep, the spring return versions.

Two years ago one of the Honeywell spring return s plan valves at mother's failed on so these are not without issues.
In their infinite wisdom Honeywell decided that the best way to secure the fixed end of the return spring was a plastic tab since it's a well known fact that plastic never goes brittle in the presence of heat. Both valves now feature a spring secured to the metal chassis work pk screws
Then just before Xmas I discovered that my hot water was at about 10 billion degrees because the all plastic tank stat had become brittle and disnitigrated. Sadly replaced with another all plastic affair as that's all the local merchant had on the shelf

Regarding y/s/w/et all sytems they mostly seem to be tinkering around the edges with valves and priority. None of this seems terribly difficult to change on the fly
I'll probably end up running something custom anyway as I'd like to direct heat the tank leaving the coil free for solar and I have some other oddball ideas. I figure if I go S plan to start the rest is just playing with software and sensors (maybe a bit of pump speed or opentherm too)

Anyhoo, I think with some insight and nudging from the replies here I've arrived at my boiler location. It will go in the upstairs airing cupboard where the hot water cylinder is.
If all goes well I can reuse the extant gas pipe but if that goes mammory verticale an external pipe run is still an option

Again many thanks for the input folks