Couple of questions about central heating from a Squirrel

[tangledfooted]

Once again I'm a bit confused - so I turn to the amazing wealth of experience and knowledge on this website.

 

Im about to fit a couple of radiators and a back boiler to my squirrel. I intend to set it up as a gravity system with 28mm copper high flow and low return and an expansion and feed tank. Not too complicated. BUT I'm not entirely confident that the whole system will have enough slope to facilitate a good thermo-syphon - it might all get a bit tight under the gunnel by the time I get to the second radiator.

 

So I thought it might be a good idea to incorporate a circulation pump on the return pipe as a bit of insurance or just to assist the thermo-syphon.

 

Is this a good idea?

 

Do I need to have some kind of by-pass around the pump if so what should it look like? Do I need a check valve? swing valve in the bypass?. If Im using 22 or 28 copper either side of the pump should the by-pass be in 15mm? The pump will probable have 1/2inch connections.

 

If I fit a pump I'd like to control it with a pipe thermostat on the flow at the stove set to action the pump when the temperature hit 85C. Were can i get hold of such a thermostat. I can't find anything on ebay?

 

Advice please.

 

[peterboat]

I have a squirrel back boiler in my stove the stove is a tim sistems magic stove but the backboiler fits it heats the calorifier and 4 rads you can get the pipe stat from screwfix or B AND Q they might call them a tank stat but its the same thing. My system is fully pumped because that was what was already there.However as long as the stove is in the stern and the rads are uphill it will work as I have just fitted this system to a friends boat and it works fine. We thought that we might need a pump but not so

 

Peter

[PaulG]

Once again I'm a bit confused - so I turn to the amazing wealth of experience and knowledge on this website.

 

Im about to fit a couple of radiators and a back boiler to my squirrel. I intend to set it up as a gravity system with 28mm copper high flow and low return and an expansion and feed tank. Not too complicated. BUT I'm not entirely confident that the whole system will have enough slope to facilitate a good thermo-syphon - it might all get a bit tight under the gunnel by the time I get to the second radiator.

 

So I thought it might be a good idea to incorporate a circulation pump on the return pipe as a bit of insurance or just to assist the thermo-syphon.

 

Is this a good idea?

 

Do I need to have some kind of by-pass around the pump if so what should it look like? Do I need a check valve? swing valve in the bypass?. If Im using 22 or 28 copper either side of the pump should the by-pass be in 15mm? The pump will probable have 1/2inch connections.

 

If I fit a pump I'd like to control it with a pipe thermostat on the flow at the stove set to action the pump when the temperature hit 85C. Were can i get hold of such a thermostat. I can't find anything on ebay?

 

Advice please.

 

I've got a similar system on my boat.

 

I have a 12V pump fitted but don't use it as it's noisy and I find that the convection system works well enough without it. I don't know if there is a bypass. If you need to know I'll try and remember to take a look this weekend.

 

Thermostat could be a good idea. This one might fit the bill - doesn't quite hit your 85 degrees but might be near enough.

 

http://www.ebay.co.uk/itm/TEAMS-CLAMP-ON-HOT-WATER-CYLINDER-DIAL-THERMOSTAT-PIPE-STAT-INC-MOUNTING-STRAP-/281335087634?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item4180e0c212

Edited September 4, 2014 by PaulG

[tangledfooted]

So will the hot water cylinder/ pipe stat work with a 12v pump?

[gary955]

So will the hot water cylinder/ pipe stat work with a 12v pump?

Yes i think so, it's just a switch

[PaulG]

So will the hot water cylinder/ pipe stat work with a 12v pump?

It should do, depending on the current draw of your pump.

 

Unfortunately the seller doesn't give any details of the contact rating.

 

It would be worthwhile asking them before buying to make sure.

[bottle]

Oh!

 

Yes i think so, it's just a switch

 

Oh! no it's not.

 

I was going to put something similar to PaulG's post.

[gary955]

Oh!

 

 

Oh! no it's not.

 

I was going to put something similar to PaulG's post.

Whoops! Sorry.

The one I have is just a bi-mettalic switch. I assumed that it was typical

[bottle]

It probably is a bi-metal strip but It is not the operation that can cause problems it is the rating of the switch and whether it can cope with dc, many are only rated for ac.

 

An ac. switch will work on dc. but has to be de-rated to cope with the possible arcing.

[tangledfooted]

I found this item on ebay. 151084725893 .

I was thinking that a cylinder stat would turn on when he temperature was low and off when the temperature got too high. Thats the opposite of what I want. Which is a thermal switch that 'closes' when the temp is high and turns on the pump and opens at low temperatures and turns the pump off.

 

Am I missing something ? Or are these cylinder stats reversible in some way.

 

I think the pump is rated at 3amps.

[PaulG]

I found this item on ebay. 151084725893 .

I was thinking that a cylinder stat would turn on when he temperature was low and off when the temperature got too high. Thats the opposite of what I want. Which is a thermal switch that 'closes' when the temp is high and turns on the pump and opens at low temperatures and turns the pump off.

 

Am I missing something ? Or are these cylinder stats reversible in some way.

 

I think the pump is rated at 3amps.

You can order this item in "normally closed" (NC) and "normally open" (NO) configurations.

The NC version effectively switches "off" at the set temperature, and the NO version switches "on".

[tangledfooted]

So an NO at 90c should do the job. Or should I go for 70C?

 

Any thoughts on a by -pass - is it necessary?

[peterboat]

So will the hot water cylinder/ pipe stat work with a 12v pump?

It does with mine and it did in my previous boat for 6 years

 

Peter

Also both tank stats I have are either NO or NC depends on how you wire it

 

Peter

[tangledfooted]

Thanks Peter

That makes sense now.

[smileypete]

Maybe give gravity operation a go, but premix any antifreeze.

 

Failing that there's pumps from £20ish on Ebay, best install with outlet pointing up so they self bleed.

 

Would have thought a cylinder stat would switch a small DC pump OK.

 

cheers, Pete.

~smpt~

Edited September 4, 2014 by smileypete

[tangledfooted]

Thanks Peter, Pete and all. So looks like I don't need a by-pass and that in the event of a pump failure the thermosyphon will work throw it. Get a cheapish pump if necessary and use either a contact thermo switch or a cylinder stat but wired for normal open. Cheers.

[David Mack]

A centrifugal impeller pump should allow convection currents to flow just fine if the pump is not running.

If you put a bypass without a NRV it will shortcircuit the pump, rendering it pointless. If you fit a bypass with NRV, then unless it has a VERY light spring the convection current won't overcome it to give any flow. So basically there is not much point in having a bypass.

 

I would be inclined to design and install the plumbing on the basis of gravity circulation only, but have a location where if necessary the pipe can be cut and a pump inserted. That way you can try the gravity circulation option first.

Edited September 4, 2014 by David Mack

[blackrose]

Personally if the system isn't that long and you're using 28mm dia pipe for your main run then I wouldn't bother with the pump. I don't think the slope of the main run is really that critical, but instead of 90 degree corners try using 2 x 135 degree elbows to make the corners more rounded. That should give less resistance to the corners of the main run.

 

[smileypete]

If there's reasonable height difference between BB and rads, and it can 'self bleed', then it should circulate OK.

 

IF not, one way to improve circulation may be an injector tee, eg:

 

 

http://www.torrens.org.uk/HowTo/Injector/

 

Best place might be an elbow between return pipe run and backboiler (so rotate above diag thu 90°), maybe fit a tee now just in case and blank off the spare end.

 

cheers, Pete.

~smpt~

Edited September 5, 2014 by smileypete

[blackrose]

Apologies, my post above assumed that there was no calorifier in the system. If there is and it has standard coils (rather than wide bore), then you'll probably need a pump.

[tangledfooted]

Very much like the venturi T. But positioning. The 28mm return comes in a bit below the lower connection for the back boiler, The pump has an natural 90degree in/out which would bring me vertical for a 90 or two 45s into the boiler. I was thinking of starting the by-pass with a T up from the horizontal then a 90 to bring it back the the other side of the pump on the vertical before the turn into the boiler. So T would put the Venturi T at the point on the vertical where the bypass rejoins the pump return. IS that right?

[smileypete]

Ah OK, I'd just test it without pump and with 100% water, otherwise could be a lot of fiddly plumbing for nothing.

 

Then dump the water and if all is good fill with premixed AF, if it won't thermosyphon then time for Plan B....

 

cheers, Pete.

~smpt~

[tangledfooted]

Just an update: Firstly thanks for all the advice. I had finished the plumbing and filled up with water and found leaks at the pump and on one solder joint. I went to tighten up the pump joints and managed to snap the pump in half. 30 litres of water heading for the bilge via the newly laid engineered oak flooring! Cleaned up with old towels removed the pump fixed the solder joint and filled up again. No leaks. Lit the fire and had heat at the far radiator in half and hour.

 

I managed to get a nice slope up just following the gunnel - keeping the flow pipe 4 inches below the gunnel. I used 28mm from the boiler to the first radiator and then 22mm on to the second. 15mm on to the expansion tank. I used full bore 15mm level valves on both radiators and no valve at all on the returns from the radiators. I kept the radiators parallel with the gunnel so they slope slightly up and join the flow to the radiators at the higher end further from the boiler so they would self bleed ( thanks Smilypete) and joint the return closer to the boiler. The return pipe is parrellel to the flow until it has to rise to the lower entrance of the back boiler. Thats where I put the pump with the venturi. So inspite of the pump being absent and there being some restriction on the return with an extra 90 degree and the venturi the whole works really well - even with a full water tank.

 

The only concern is that i didn't bother with a return from the expansion tank -reckoning that the last radiator would do the job - as an after thought I took the level of the last valve so i couldn't close the valve. Do you think I was being stupid/lazy not adding the (feed) to the return? I just could'nt see why I would need it.

[smileypete]

Sorry to hear about the pump , the connections do look a bit fragile. Glad to hear it's working well on thermosyphon.

 

The only concern is that i didn't bother with a return from the expansion tank -reckoning that the last radiator would do the job - as an after thought I took the level of the last valve so i couldn't close the valve. Do you think I was being stupid/lazy not adding the (feed) to the return? I just could'nt see why I would need it.

 

Not 100% sure what you mean there, a sketch or piccy would help.

 

Sounds like the feed pipe from the header tank goes into/through the last rad, if so provided the rad can't be turned off then it should be OK.

 

cheers, Pete.

~smpt~

[Alan Saunders]

Thank you for the feedback Tanglefooted. 28mm pipe, though dificult to bend it will enable your thermosyphon and (uninsulated) warm every compartment that it passes through. I have seen a 70' boat that had no radiators, only large (3" or 4"?) iron pipes.

 

Even though it is the ideal arrangement, a thermosyphon system does not need a 'continous slope'. The important thing is that each radiator is higher than its predecessor.

 

The suppliers and manufacturers of my boiler recomended additional thermostats. One to only run the pump when the boiler reached a sufficient temperature; to avoid condensation and subsequent corrosion. Another to run the pump if the boiler temperature became excessive; to dump heat and avoid internal corrosion due to 'local boiling'.

 

They also recomended an injection-tee (smpt's venturi) which would initiate the thermo-syphon sooner and hardly impede it. Like smtp's diagram this can be made up from standard components.

 

BTW, even in this 'balmy' weather you can run the system flat-out to determine its capacity. If it can raise the cabin temperature from 20C to 40C then it will also raise the temperature by 20C from -10C to +10C in a cold winter.

 

HTH, Alan