Please comment on our stove set up

[goosebump]

Hello,
We just placed an order for Woodwarm 12 with split saddle and roof boilers. Hot water from stove will gravity feed a 210l thermal store positioned almost directly above. There will be a pumped circuit for the radiators, heat sink rad in the bathroom. Thats the easy bit. My understanding of plumbing is patchy so would appreciate a double check that what the plumber says makes sense:

there are no pipe/flue stats included in this system. The plumber says thats fine, due to the gravity feed and the fact a store is being used.
Stove has no thermostat to control airflow (we could order one if this is sensible?) Woodwarm say there is no real need for one once you get to know how the stove works.

Is this right? Whats your view?

[Tigger]

Hi Goosebump,

My own opinion is that you should fit the thermostat control for the airflow. 

Yes, you can manage it manually and prevent the water from boiling however if you happen to go to bed one night and leave the air vent open, you'll be woken up by the loud rumbling noise your hot water cylinder will make when the stove starts to boil.  I speak from personal experience of the set up in my parents house with an open fire with back boiler.......

[goosebump]

Thanks Tigger,
To be honest, I thought it was a bit of a "no brainer" but the supplier is fairly sure that in the long run (ie once youve got the stove sussed) you dont need it.  Do you know about the pipe stats?

[Stuart]

Using gravity flow only, the water in the tank wont be so hot unless the fire has been going all day.

I would be simple to wire a thermostat to the top of the tank, and connect it to the central heating pump so it would automatically dump excessive heat into the rads. rather that boiling into the expansion tank (being well supported and able to hold boiling water with a copper ballcock) and out the (copper) overflow.

that hot domestic water coming out of the thermal store may be scalding hot so good idea to fit a Thermostatic mixing valve to make sure its at a safer temperature.

[goosebump]

Stuart - thanks for the comments.  Why does the gravity feed mean the store will take longer to get hot?  The water has only to travel a couple of metres from stove to store?

[dhaslam]

When you are using a pumped radiator circuit  there is a possibility that the pump will  prevent  water circulating in the cylinder unless there is a bypass  to allow the pump to draw hot water through the cylinder coil.   Once you have a boiler large enough to heat the cylinder and radiators  the cylinder should always be  reasonably hot   but  you may need to adjust temperatures  on the pump thermostat to avoid cooling the cylinder.   The pump thermostat should be fairly close to the boiler.  This will start the circulation a bit quicker and  prevent the stove thermostat, if fitted, from closing prematurely.   Gravity circuits can be quite slow to get started  although some of the delay is in heating the water in the boiler first.   

[biff]

hi goosbump,
          the trick with the gravity system is to ensure that the bends are nicely rounded( in the proper bender) and that the flow and return leave and return to the boiler as gentle as possible,compression elbows close to the boiler will cause turbulence and the system will bump and bang for eternity.
      ensure that the flow rises gently to the storage tank and that there are no hollows or sags in the pipework which must be copper and no less than inch and a half in diameter for quick recovery.
     it is important to fit a thermostat enroute to the expansion tank which will trigger the pump to send the excess hot around the rads, and also a non return flap valve to stop the pump from circulating  through the gravity pipe and bypassing the boiler.
       there is a nice little system waiting in there,just draw it all out before you start,
      placky pipe dont work well in the gravity system,due to the possible excess heat and also because the molicules in the plastic create a drag on the water. note that drops of water run along the surface of the copper like ballbearings and that they tend to flatten out on the surface of the placky,
                  good luck,
                                   biff.

[Micol]

Goosebump,
I'd second Biff's comment about having a non-return flap valve in the gravity circuit (in the return) for the reason Biff mentions but also to inhibit hot water in the store from circulating down through the boiler and losing tank heat when the stove isn't on.  My previous installation didn't have a NR valve and we kept losing heat all over the summer (when the tank was heated by the oil boiler).
We also had a Woodwarm 9kW with split saddle and roof boilers - great stove - dead easy to light and run - I got discount buying from Simon Keeping (google him) - he designed and made the Woodwarm range and sold the business (Metal Developments) to his employees a few years back, but he still sells them.  Worth a go.

Micol

[noelsquibb]

Goosebump

Weve just done our first winter with the fire you have purchased and we have no problems with managing the air flow manually.

Probably the most useful thing for managing it is the magnetic thermometer that is permanently attached to the top boiler.

This allows us to drive the fire quite hard when the heatstore is around 55c-65c ( top & bottom temps ) and back it off when its been raised to around 65c-75c with the return flow keeping the boiler temp reading around 70c and the fire ticking over. This way we can drive it hard to heat the water then let it tick over for room heat.

If we go out we throttle the fire right back to minimum but if you are thinking of cooking water whilst you are out
a stat for air control could be useful.
Now youve just got to work out how to load logs when you are out.

Well impressed with the fire, apart from its appetite for wood.

Agree with the flap valve but apparently they need to be close to horizontal to work in a gravity circuit

noel

[goosebump]

Thanks all for the replies - the best forum by far for sensible replies!  We have just opted to go for the thermostat.  As for the rest of the system, the plumber has finally tired of me pestering and invited me out on a job with him to see a system he has recently installed so we can talk the whole thing through.  I will be asking about pipe bends, stat positions and non return valves!
Thanks again.

[Solal]

Don't expect  your  installer  to  fit an nrv  on the feed and expansion  pipe to your  stove or on any section of the feed and vent arrangement!
If  crud   or sludge  jams  the valve  say over a  summer period  of  inactivity  then  upon re igniting   the stove    the   boiler  may empty  and become  extremely hot, with possibly  disastrous  consequences.
I think BS6700  deals with the finer details.

I expect  those who are having  "reversed"   circulation  through their stove  when  unfired  probably have their stove   "directly"  connected  and another heat source  heating the store.

What type of thermal  store  are you installing?  Will it provide DHW?

[Brandon]

what that lot said, and don't take him seriously if he cant pull bends in 28mm.

[goosebump]

Solal - the store is for central heating and hot water - not sure on the specifics.  I appreciate its small, we opted for a store more for ease of installation than anything else.

[Solal]

When you are using a pumped radiator circuit  there is a possibility that the pump will  prevent  water circulating in the cylinder unless there is a bypass  to allow the pump to draw hot water through the cylinder coil.

What type of layout does this refer too?
I think you mean  a directly  heated  thermal store  with the stove connected top/bottom at the store  and  the CH return  then being balanced  between  an unused  indirect coil  at the bottom  and  the store  in  order  to reduce turbulence?

Would it not be easier  to  have a circulator  with a low flowrate?
Or regulated to acheive a low flowrate!

[Brandon]

Would it not be easier  to  have a circulator  with a low flowrate?
Or regulated to acheive a low flowrate!

or three pipe and injector tee, problem solved