central heating pipe sizing.

dvae

in the process of renovating an old house.
the house has never had a heating system other than an open fire.

i am now at the stage of fitting a stove and laying the
pipes for the flow and return to the radiators. (gravity fed system)

I was planning on having the flow and return pipes at 22mm with 15mm branching off to the rads.
If I use pex piping for the f&r will the inside diameter of the 22mm pipe (17mm ish) restrict the flow
of the water to the rads?

Is using 22mm pex for the flow and return common practice or a bad idea?

thanks.

dvae

anybody?

John.G

If relying on gravity circulation (no circ pump) then pex will not do the job, even if you have a circ pump and you get a power failure the flow temp can rise to 100C which may be above the max permissible temp for pex.
3/4" pex is 16.7MM ID and 3/4" copper is 19MM ID.

corkgsxr

Also depends on house size.

Small old bungalow vs country manor.

Need proper detail to advice.

dvae

thanks for the reply guys.

the house is a small single story cottage with 6 rads.
the stove will be a Stanley erin or similar, about 14kw
boiler output. the plan is to eventually build a small extention
to the rear of the house, (another bedroom) so the boiler can
handle another rad or two.

Dtp1979

If you don’t know that 22mm pex isn’t suitable for gravity circulation then you have no business installing what could potentially be a bomb. You’re using the wrong type of pipe and certainly the wrong size.

dvae

Dtp1979 wrote: »

If you don’t know that 22mm pex isn’t suitable for gravity circulation then you have no business installing what could potentially be a bomb. You’re using the wrong type of pipe and certainly the wrong size.

your 100% right, I certainly have no business installing a central heating system but unfortunately
because of my circumstances I have very little choice.
I have done quite a lot of research and im also quite competent when
when it comes to most jobs.

certainly when im finished I will have somebody more qualified to look over
my work before I fire the system for the first time.

anyway ive decided to swap out the 3/4" pex for copper.
pipe.
most of the diagrams ive looked at use 3/4" pipework for the flow and
return, but none said if pex was suitable.

I guess from the above post, its not.
folks, all im asking here now is, is 3/4 copper suitable for the flow
and return? if not what is?
cheers......

corkgsxr

Are you pumping it around?

Is there a gravity circuit to the cylinder?

Dtp1979

corkgsxr wrote: »

Are you pumping it around?

Is there a gravity circuit to the cylinder?

It’s meant to be gravity.
Op, you say you’ve done extensive research into this yet you don’t even know what pipe size to use.

corkgsxr

Dtp1979 wrote: »

It’s meant to be gravity.
Op, you say you’ve done extensive research into this yet you don’t even know what pipe size to use.

Mm seems alright.

For what its worth i done a system like you want in a small 2 bed bungalow

Cylinder 2 foot higher and basically next to stove. In 1" copper with minimal bends.

Off that I took a 3/4 copper off each to supply the rads.

I done it with stat taking the reading off cylinder flow activating pump for rads.

That ment all rads got a good flow. As they were pumped.
Its favored to rads than cylinder.

Worked very well. If the power failed the cylinder gravity took over

Dtp1979

corkgsxr wrote: »

Mm seems alright.

For what its worth i done a system like you want in a small 2 bed bungalow

Cylinder 2 foot higher and basically next to stove. In 1" copper with minimal bends.

Off that I took a 3/4 copper off each to supply the rads.

I done it with stat taking the reading off cylinder flow activating pump for rads.

That ment all rads got a good flow. As they were pumped.
Its favored to rads than cylinder.

Worked very well. If the power failed the cylinder gravity took over

That’s the only way to do it by right. Rads are the secondary circuit, so should be pumped. The op initially was talking about doing the primary circuit in 22mm pex, which is wrong. If he/she hasn’t basic fundamentals like that right then they shouldn’t attempt anything at all.

antoinolachtnai

Dtp1979 wrote: »

That’s the only way to do it by right. Rads are the secondary circuit, so should be pumped. The op initially was talking about doing the primary circuit in 22mm pex, which is wrong. If he/she hasn’t basic fundamentals like that right then they shouldn’t attempt anything at all.

What the OP proposes to do is fundamentally very dangerous. Please do not do any of this. If you can’t afford to get an experienced professional to do this properly, don’t do it at all. If you are determined you want to do a quick and dirty job, buy an oil boiler. Even if you do a bad job you are unlikely to kill or maim anyone (other than yourself anyway, and the death will at least be quite quick, rather than slow and painful). I am not joking. This is really that serious.

Dtp1979

As my old plumbing instructor in Shannon used to say, any idiot can plumb an automatic system (oil boiler), but you can’t turn off a solid fuel fire

corkgsxr

Dtp1979 wrote: »

As my old plumbing instructor in Shannon used to say, and I’m idiot can plumb an automatic system (oil boiler), but you can’t turn off a solid fuel fire

Only type of heating that can genuinely violently explode

Dardania

corkgsxr wrote: »

Only type of heating that can genuinely violently explode

Similar to nuclear power as it happens...