Advice needed - Installing a solid fuel stove and buffer tank

iwb

I have installed a second hand solid fuel stove in my garage and had a qualified person put the flue in. Now it's time to plumb it all together. I have a 1,000 litre buffer tank which has a coil and several connections to the main volume of water.

I have a plumber lined up but I want to be sure I know best practise for this as I have gotten bad advice in the past. I know these things can be dangerous. I will put a UPS onto the circulating pump for safety. I intend to get a hybrid solar solution in place in the future which may mean I can remove the UPS.

Here's my take on it so far: The stove needs to feed the coil in the buffer tank. 1" copper pipe from top of boiler to the top of the coil, 1" copper from bottom of coil to boiler. Circulating pump which starts from a pipe stat (keeping it simple for now). Expansion vessel and air separator. Does this circuit need a water source to refill it? Can it be mains pressure or has to be a tank? What else am I missing?

The buffer tank is then plumbed 3/4" to the hot water cylinder. Straightforward as I have a spare coil on the cylinder. It has a circulation pump and some sort of controls. It is also plumbed to the main feed into the house. I could use a three way valve to choose existing oil boiler or buffer tank. it needs an expansion vessel also.

Calahonda52

Expansion vessel, no way unless you want to build a bomb!

1" pipe from stove must vent to air and you must also have an open refill: google back boiler plumbing

Not from mains, you need to reduce the risks so keep it simple

To get a serious heat gain from buffer to DHW cylinder, you will need a decent delta T across the coils so you will need 75 or 80 C in the buffer if you want 60 in the DHWC

What's the pipe run from buffer to DHWC?

How big is the DHWC?

iwb

Thanks for the quick reply. I'll use copper from the buffer tank to hot water tank I think. 3/4" copper in the other coil from the oil boiler. It's a 300 litre cylinder.

Why the vent to air, is it a safety thing? I was going by some diagrams I saw online and it didn't show this? Not exactly the same setup though.

In the diagram above, there's a coil on the heating side also which I don't have. Does that side need to be vent to air if no coil? If so, can it be the same tank above or two separate ones as shown here?

Regarding the delta, I haven't tried it yet but I was hoping to get 70 - 80 degrees in the buffer. The oil is there to boost it too though so not very concerned.

iwb

Also, do I need a Laddomat to regulate the boiler to buffer tank temperature? I don't really understand the need for it but my plumber mentioned it before. The other thing that seems to come up is that the boiler might be better directly feeding the tank, instead of through a coil as the heat won't transfer effectively through the coil and will come back too hot.

Lenar3556

A stove, and most other uncontrolled solid fuel applicances must be open vented. I.e you would typically have a feed and expansion tank which auto refills by a ball cock.

Ideally there would be no need for a circulation pump, and the primary circuit should circulate on gravity/temperature alone.

Is it a very big stove?

Lenar3556

https://www.boards.ie/discussion/comment/121443105#Comment_121443105

A big difference in temperature between stove flow and return will lead to condensing for which the stove isn’t designed, and would rot the boiler prematurely. The Laddomat is a mixing valve which prevents under temperature water entering the boiler on the return side.

The above would be less of an issue with a coil arrangement than circulating water directly between the stove and buffer tank, and this is probably the route I would be going.

Again it’s best that the 1” stove circuit is clear of any valves / laddomats etc. and is allowed to circulate on gravity.

Out of interest, have you done the sums on the financial viability of this? Quite a bit of work between building and running it!

iwb

So, if I go with the coil, it would transfer enough heat by gravity? The boiler wouldn't overheat?

Sounds so much less complicated and no worries about power cuts from a safety point of view. To be clear, the boiler is on the same level as the buffer tank. Is that a problem gravity wise?

I didn't do a really in depth financial analysis but I have lots of firewood and I don't like to burn oil. Not many choices in the country. I bought it all second hand, so it wasn't as expensive. Also, I have an office in the garage and the flue will heat that, saving more electricity or oil.

Lenar3556

https://www.boards.ie/discussion/comment/121444714#Comment_121444714

The answer to a lot of that will depend on the individual spec of the buffer tank and the coil within it. If you can find the make and model the manufacturer should be able to tell you what the coil delivers to the volume of water in the buffer tank (in KW) at a given temperature.

iwb

Thanks. I don't have any info on the tank. Can the copper between stove and tank be level or with a 50mm rise maybe?

iwb

I'd really like to move this along. Anyone willing to advise remotely? I'm happy to pay for the help.

Lenar3556

https://www.boards.ie/discussion/comment/121447090#Comment_121447090

There is going to be an element of ‘suck it and see’ with this in order to establish what will work best, particularly given that there is no spec for the buffet tank.

It it were me;

1. I would install a galvanised steel feed and expansion tank at the highest point available, and in a well ventilated space. Run overflow pipe to safe location outside.
2. Run 1” flow and return to the buffer tank coil. The pipe from the top of the stove entering the bottom of the coil on the tank, so as to encourage a gravity path.
3. Install a circulation pump on a parallel path created in the pipework, so that I could increase the flow if necessary. I.e if I had a large fire on and gravity circulation was inadequate.
4. Install a 3 bar safety valve at the stove and pipe to outside.

Would be interested to hear how you get on.