Repurpose old unvented hot water tank

[Spedley]

I have an old Valliant uniSTOR 210/2 S and I want to repurpose it as an vented*tank.
I used to have a pool with a 40kW diesel boiler. The pool is gone now but I want to repurpose the boiler to run a radiator in my garage.
My plan is to heat up the 210L tank and then pump that water through a 2kW(ish) radiator for heating.
A neighbour was replacing their Valliant tank (not sure why really?) but it is still fully functional and in decent condition.

How do I convert it or use it as an vented* tank? I'm doing it myself on a budget and don't want a pressurised system.

* corrected from unvented.

 

[Madrab]

Do you mean re-purpose it as a vented cylinder or even a thermal store (TS)? Guess it could be done, it would need a header tank to keep the store topped up and a location to vent to and then pump the rad water through the coil.

Using a 40Kw diesel boiler though is madly oversized just to maintain a 210L TS and that just to run a 2kw rad, it really is a sledgehammer to crack a nut.

 

[Spedley]

I don't plan on a header tank, just taking water from well below the top of the tank, probably from the pressure relief valve pipe. My only real issue is that I dont know enough about the baffle or bubble. I put an inspection camera in but does seem to help. How do I disable that?

As for overkill, yeah but it's already there unused. Taking a 1.5 ton car half mile to get 20Kg of shopping is overkill ... but like I say, it's there so use it.

 

[Harry Bloomfield]

I used to have a pool with a 40kW diesel boiler. The pool is gone now but I want to repurpose the boiler to run a radiator in my garage.

Better/cheaper/simpler - If you want to heat a garage/workshop, buy yourself a cheap diesel heater. These have a combustion air intake, and exhaust, which both need to be out through a wall, plus a larger heated air intake and outlet. Up to 8Kw of heated air, thermostatically controlled, and can be run on diesel, heating oil, paraffin, or Jet A1 from your local airport, which ever you can source cheapest. They do need a 12v supply, such as a car battery, or similar power supply, but they are very efficient on fuel use.

I use one, in my garage workshop, it provides instant heat, and only when required.

These heaters can be had for £60 to £100.

 

[trojanhawrs]

I don't plan on a header tank, just taking water from well below the top of the tank, probably from the pressure relief valve pipe. My only real issue is that I dont know enough about the baffle or bubble. I put an inspection camera in but does seem to help. How do I disable that?

As for overkill, yeah but it's already there unused. Taking a 1.5 ton car half mile to get 20Kg of shopping is overkill ... but like I say, it's there so use it.

Without a cold water feed and header tank I'm pretty sure you'll airlock the system through evaporation.

 

[danfre]

Little knowledge, sounds dangerous

 

[Madrab]

I don't think the Unistor has an internal baffle, I believe it uses an external EV.

I don't plan on a header tank, just taking water from well below the top of the tank, probably from the pressure relief valve pipe.

Nope, 'fraid not - a vented cylinder needs a header 'tank' as in a F&E. You can't set it up just to heat the water via the coil and then just pump it to the rad without a vent as it's primary safety outlet (hence the name) and that normally would vent into the F&E.

As a thermal stoire and heat the rad water via the coil then that would also need a F&E cistern.

 

[Spedley]

"I don't think the Unistor has an internal baffle, I believe it uses an external EV"

That kind of makes sense as this is the photo from inside looking up at the main draw pipe. The centre pipe is only about 5" long until it exits. It doesn't look like a baffle and has nowhere to move, however it doesn't look like the top of a tank either.

 

[robinbanks]

You need to have a G3 certificate to work on unvented hot water systems. I'm guessing from the nature of the questions you're asking, that you don't have one. Please get someone in who is; I've seen more than one house rendered uninhabitable by the resulting explosion from tank failure - 200l of near boiling water erupting through a wall is a major risk to life

 

[Spedley]

Ah yes, after a bit of research you are right! The uniSTOR does have an external pressure tank and no baffle/bubble - which is great news! That means the tank is not an unvented tank, just that it is strong enough to be used in an unvented system. There's nothing stopping me using it as a vented tank for gravity fed system.

 

[endecotp]

You need to have a G3 certificate to work on unvented hot water systems.

He’s not actually proposing to make an unvented (pressurised) system. He has used that term in error in the first post.

 

[Spedley]

"He’s not actually proposing to make an unvented (pressurised) system. He has used that term in error in the first post."
Ooops, so I have. Thanks for that - edited now.
For some reason I type it the wrong way around, probably because vented=unpressurised, unvented=pressurised. Think my head is thinking pressure and my hands type venting.

 

[trojanhawrs]

"He’s not actually proposing to make an unvented (pressurised) system. He has used that term in error in the first post."
Ooops, so I have. Thanks for that - edited now.
For some reason I type it the wrong way around, probably because vented=unpressurised, unvented=pressurised. Think my head is thinking pressure and my hands type venting.

Your head isn't doing much thinking at all if you're planning to do it without a header tank.

 

[Spedley]

That was a bit rude trojanhawrs.
I don't see a need for a header tank. The boiler already has a header tank but the storage cylinder doesn't need one - the water is not used, it is circulated. I will also control evaporation, probably through a gauze. Water flow is minimal and if it gets an air pocket I'll walk across the room and top it up.
It's a non commissioned system in a garage used by the person who built it and will require far less maintenance than a wood stove.

How about this idea, I'm sure you'll love it ...
I'm also considering not using the heating coil but plumbing the boiler output directly into the tank. That has several advantages, one being I can use the boiler's header tank (if I raise it a bit). The main benefit being that the coil is only rated for approx. 22kW so it may not be able to cope with the boiler output of 40kW. I'll have to put inhibiter in both loops anyway so why not just get rid of one loop?

 

[trojanhawrs]

I don't see a need for a header tank. The boiler already has a header tank but the storage cylinder doesn't need one - the water is not used, it is circulated.

Nor is the water from the boiler used, and yet it has one.

How about this idea, I'm sure you'll love it ...
I'm also considering not using the heating coil but plumbing the boiler output directly into the tank. That has several advantages, one being I can use the boiler's header tank (if I raise it a bit). The main benefit being that the coil is only rated for approx. 22kW so it may not be able to cope with the boiler output of 40kW. I'll have to put inhibiter in both loops anyway so why not just get rid of one loop?

You could do that, that's a thermal store. How many tappings do you have on the cylinder though? You need flow and return to boiler, and the same for radiator. If you're not using the heating coil (and not using the top draw off pipe which you'll have to leave open to vent regardless) what does that leave you with?