Underfloor heating, any plumbers?

[yorkie_chris]

Originally Posted by skeetly

A 'simple pump the hot water round a loop' type system that you envisage might result in the circulating water getting too hot for the plaggy pipe to handle.....
This would be a failure

True. But I think we will use somewhere around 150m of pipe on 4 or 5 different circuits.

That's quite a lot for the size of boiler from what rich says, in fact, is this even going to put out an appreciable amount of heat? Or am I going to end up with a perfectly engineered, double fail-safed system which will barely warm up its working fluid lol.

[skeetly]

Originally Posted by yorkie_chris

Hmmm.
SV thermostat housing? Chop a radiator in half and weld it up so it will fit between joists, when the thermostat pops it will heat the radiator not the pipe coils.*

Sv rad is designed to have air forced through it so wont work so well...

Originally Posted by yorkie_chris

But, with an open system it will never get over 100c anyway (with the tank in the loft I reckon that is a 7m head so only about 68kPa, negligible effect on boiling point). So, depending on what the manufacturer says I think the tubing should be able to handle the max temperature OK.

A long as the heat dissipates fast enough, it will be a long length of pipe with bends with a poor pump doing its best; might need 2 pumps

Originally Posted by yorkie_chris

*My stepdad's a sparky, he says the first use of underfloor heating he saw was a guy bolting a pair of normal radiators underneath the floor!

Normal Rads do most of their work by convecting so this wouldnt work very well

Originally Posted by yorkie_chris

The problem is, what happens if the pumps switching is delayed, there can be very little convective movement because the stove is above the cooling coils.

I don't think an explosion is possible under steady state, because the system is not sealed. But, a large amount of steam could be generated when the pump is switched on when the stove is hot and has formed a steam bubble in the boiler. This I don't like.

If you put the stat in the right palce and adjust it right the pump will kick in pretty quick. Most boilers should be able to 'kettle' a bit before killing you anyway...
If they arent some cheap chinese impor...oh wait.

[skeetly]

Originally Posted by yorkie_chris

True. But I think we will use somewhere around 150m of pipe on 4 or 5 different circuits.

That's quite a lot for the size of boiler from what rich says, in fact, is this even going to put out an appreciable amount of heat? Or am I going to end up with a perfectly engineered, double fail-safed system which will barely warm up its working fluid lol.

That can happen too

[yorkie_chris]

I could hydrostatically test the boiler, but that won't tell me a thing unless I destroy it and make another. But that won't tell me a thing because mine will be made differently 'cos I can't guarantee materials, so I'll have to destroy that and make another!

But, we can put the thermostat right behind the boiler so it will get the temperature quickly.


What I did think of was some fair sized body of water in between the fire and pump. So if a delay caused a temperature "surge" it would be well diluted before reaching anything sensitive.

[yorkie_chris]

Here is the big safety question.

This system is open to the atmosphere via a pipe looped over at the top pointing down into the expansion tank, it's also got a pipe to the bottom of the expansion tank.

What could possibly cause this to go bang short of both of the feeds to the boiler becoming sealed off?

Flash steam if the boiler is allowed to get glowing white then gets cold water dumped into it? Would that go bang or just shoot steam-clean my loft?

[skeetly]

Originally Posted by yorkie_chris

But, we can put the thermostat right behind the boiler so it will get the temperature quickly.

On the boiler would be best

[skeetly]

Originally Posted by yorkie_chris

Here is the big safety question.

This system is open to the atmosphere via a pipe looped over at the top pointing down into the expansion tank, it's also got a pipe to the bottom of the expansion tank.

What could possibly cause this to go bang short of both of the feeds to the boiler becoming sealed off?

Flash steam if the boiler is allowed to get glowing white then gets cold water dumped into it? Would that go bang or just shoot steam-clean my loft?

It should be fine. Sometimes the boiler can 'kettle' (small steam bubbles) if you cant dump heat from the system fast enough. You need to make sure the pipe going back to the header tank is long enough and wide enough so that you dont start getting hot water expanding into the header tank.
There was a fatal accident a while back when this happened with an immersion heater system ffs. Plastic header just got so hot it folded over and dumped gallons of boiling water through the ceiling onto some poor woman while she slept

You do have 7m of head though so you should be OK.
It all comes back to controlling the heat source though...

[yorkie_chris]

That is dodgy! But should not be possible with a steel tank.

It is controlling the heat source which is problem. I am looking at design of dunsley yorkshire stove and thinking how basic ours is! Draft control on ours is just a flap on the back of the ash box which does not seal well. I am thinking I may weld this up, and weld a 3" pipe onto it with a ball valve. That way could even duct in cold air from somewhere.

[skeetly]

Originally Posted by yorkie_chris

That is dodgy! But should not be possible with a steel tank.

It is controlling the heat source which is problem. I am looking at design of dunsley yorkshire stove and thinking how basic ours is! Draft control on ours is just a flap on the back of the ash box which does not seal well. I am thinking I may weld this up, and weld a 3" pipe onto it with a ball valve. That way could even duct in cold air from somewhere.

Ours is a 3" metal disc on a thread so you can 'spin' it in and out.
a 1/16th gap to keep the thing over night and 3/8th to have it roaring.
Thats how fine the control is. Tiny leaks make a massive difference

[yorkie_chris]

Is yours tightly sealed enough to actually go out if the vent is closed fully then?