DHW from a solid fuel Aga

[shellac]

I have a 56 year old solid fuel Aga used for cooking and space heating. It seems a waste not to utilise the aga's hot water capabilities so I've a acquired a glass lined boiler which I intend to fit.

The aga will be connected up to a vented single feed indirect hot water cylinder (Gledhill primatic) which I've also just acquired.

The Aga system will replace the current DHW system of an immersion heater and a direct cyclinder.

A couple of questions:

1. Does the Aga still require it's own f&e tank or will the primatic serve that purpose?

2. Does the Aga flow primary require it's own vent pipe when linked to the primatic?

Thanks

 

[Terrywookfit]

Primatics should not be used on SF.

 

[shellac]

Damn.....so I've bought the wrong type of cylinder? Anyone want to buy a 12 month old, unused Gledhill Primatic?

Do I need an indirect with 28mm internal coil? I've also read somewhere on the internet that it should be unlagged when used with SF Aga - is that right?

And I guess I need a high temp f&e tank for the Aga?

Sorry for so many questions. I've had a couple of plumbers round but gravity fed DHW systems seem a bit of a mystery to them.

 

[RickMoore]

You need better plumbers. Gravity fed systems aren't that complicated.

Consider a thermal store, and benefit from mains pressure hot water, rather than anything else IMHO

 

[shellac]

if funds were unlimited then yes, a thermal store would be ideal - unfortunately that's not the case.......besides the Aga and a traditional gravity fed system also gives me a heat leak radiator and believe me, my bathroom needs it!

The plumbers I've spoken to were all in their 30's and it was obvious they did not have experience of gravity fed systems. One suggested a pump would be required and the other thought a conventional radiator would serve as a heat leak.
There is one plumber, a much older guy who is highly recommended but he has a 6 month waiting list!
Rather than pay up to £1k for a bodged system I've decided to install it myself.

 

[RickMoore]

I go back to you need better plumbers. I'm in my 30's and really don't have that much experience of gravity systems in practice, relatively speaking, but still know how they work. After all it's covered in level 2 nvq's but hey ho.

The cylinder needs to be appropriatly sized for the aga and located properly in relation to the aga. Both the aga and cylinder, if it's vented, will need vent pipes over the appropriate storage cistern. Minimum 28mm pipework for flow and return between again cylinder. Ideally the cylinder wants to be directly above the aga.

 

[shellac]

thanks for the advice. The cottage is single storey. It used to be two cottages but was converted into one dwelling several decades ago. Apart from a wood burning stove in the sitting room which is lit only at weekends the solid fuel Aga is the only source of heat. The kitchen is great but the rest of the place is baltic!
When I first installed the Aga I was hoping that the heat generated would dissipate throughout the building and even removed all the doors. It doesn't work that way, the Aga draws in cold air from every room so the doors are back on.
Right now the cylinder is located in the bathroom immediately behind the Aga, the other side of what was a 3' thick party wall but the necessary 28mm pipe work can't reach it because of an internal wall at 90 degrees to the Aga.

I did intend to locate the new cylinder in an internal hallway and build a new airing cupboard in the hope that it would heat the rest of the cottage and allow for an old Edwardian towel rail to be installed in the bathroom as a heat sink. The other alternative is to place the cylinder in the loft immediately above the Aga which would be more efficient in terms of thermosyphoning but would rob me of much needed heat.

 

[SimonH2]

Starting with ... I don't know what the regs say, nor do I have experience i this area ...

Logic says that if you have the cylinder close enough, then you don't need a lot of vertical height difference to make a thermosyphon work. So if the proposed location is "quite close", and you can get the pipework to have all the right falls, then you should be able to have the cylinder in a ground floor location - though possibly it would have to be lifted up (as a minimum you'll need the bottom of the cylinder above the bottom of the boiler or you'll have some dead space that won't get heated.
From your description, I can't see why you can't get pipes to the current cylinder location. Perhaps a sketch of the layout would help people visualise your setup ?

If you do end up with the cylinder in the attic, then you might also consider hooking up the WBS to it as well - but whether that's worth it depends on your habits in terms of when you have what lit.

I'd also suggest you consider a thermal store and connect direct. It'll save a lot of considerations as you'll just have an open vented system with no worries about sizing an indirect coil to guarantee it'll cope with a "fully stoked" Aga.

BTW - I believe it is possible to have a pumped circuit, but that needs proper safety valves and stuff which I suspect add to the cost somewhat.

 

[transam]

general rule of thumb ? 3 foot thermal centres i.e centre of cylinder coil centre of heat exchanger on the aga/ boiler 3 feet

 

[shellac]

Thanks for everyone taking the time to reply.

If you think of my room layout as an inverted T, the aga is south of the horizontal and just to the left of the vertical. The bathroom is to the right of the vertical. That's probably as clear as mud!

My solution is to run the flow and returns to a new cylinder located to the left of the vertical which is a spacious inner hallway. The new cylinder can be raised 3' above the Aga boiler to help thermo syphoning.

I've had another idea too. My intention is to treat the existing cylinder as a large heat sink radiator - T off the primary flow and returns into top and bottom of existing cylinder respectively. If I strip off the insulation it should work fine as a heat sink and keep the bathroom warm. I'll probably vent it too just to be on the safe side.

Hopefully this will keep the whole system from boiling.

The wood burner is a long way off and would require a very long horizontal run which would affect thermo syphoning. I suppose I could pump it?

A thermal store would be great but right now is way beyond my means. Besides, I don't want to spend too much money as the cottage is only rented, albeit on a 10 year lease - and yes, I do have the landlord's permission!

 

[SimonH2]

I've had another idea too. My intention is to treat the existing cylinder as a large heat sink radiator - T off the primary flow and returns into top and bottom of existing cylinder respectively. If I strip off the insulation it should work fine as a heat sink and keep the bathroom warm. I'll probably vent it too just to be on the safe side.

But ideally you don't want your heat dump running continuously or it'll just cool the whole system down. Best discuss it with an expert before you get too far into the planning stages.

The wood burner is a long way off and would require a very long horizontal run which would affect thermo syphoning. I suppose I could pump it?

Yes, it can be pumped, but you'll ned to use the right safety systems - in essence there needs to be a failsafe (failure of power means it opens without external energy) means of allowing thermosyphon to a suitable heat dump (radiator in the attic). Again, something an expert could advise on.

A thermal store would be great but right now is way beyond my means. Besides, I don't want to spend too much money as the cottage is only rented, albeit on a 10 year lease - and yes, I do have the landlord's permission!

BIY heat bank (if you can find a suitable heat exchanger going spare) ?

 

[shellac]

The reason I'm thinking along the lines of the original cylinder as a large heat leak is that the new cylinder I have just been given is way under the spec recommended by Aga. They state a cylinder of 190 ltrs - mine is 120.

This has to be a system on a very tight budget.

The other option is to run the two cylinders in series? Pipe run as described but with DHW take off from the original cylinder.

I know this must all sound like a horrible compromise but does it have a chance of working and will it be safe?