New multifuel boiler stove system

[Mack5]

Hi, I am in the middle of planning a new boiler stove system for my house. As a back story I've no idea when it comes to plumbing, I've done some research and I am trying to get an idea of what is achievable and efficient. I will of course be using a plumber to do all the work, I just want as much info as possible.

At the moment all dhw comes from economy 7 immersion. I have bought a boiler stove with an output of 6kw for water heating. The economy 7 tank is around about 100 litres direct copper cylinder. It used to be fed by an open fire back boiler, the pipes have been cut and blocked off. Heating is night storage.

From days of looking over some systems, I can't see one in particular similar to my idea. I would like to move the direct cylinder to the loft space and connect this into the central heating circuit. I would also install an F+E for this circuit. On ground floor I would install an indirect vented copper cylinder, the heating coil would be fed from the very top of the direct cylinder in the loft. The cylinder would have twin immersion, top immersion for mains electricity "boost" and lower connected directly to solar panels for summertime water heating. I would have a circulating pump, but I'm not sure where this would be best placed. Either on the return from the radiators, the return from the indirect cylinder or the common return to the stove.

As I have said, I'm not a plumber, I'm a truck driver, so I'm not going to get offended if you say I'm wrong about anything. I have drawn some sort of schematic, and I will allow you to laugh a little at that. I'm also on a very tight budget, so suggestions of fitting a combi boiler won't be necessary.

Does this system look plausible/efficient?

Would the heat stored in the direct tank in the loft be enough to heat the indirect dhw tank if the fire wasnt lit?

Would it take too long to heat 100+ litres of the central heating system?

Cheers for reading.

 

[Ric2013]

It's an interesting idea and I can anticipate a number of problems with it. Will try to have another look tomorrow after work.

 

[ShaunCorbs]

Sorry but can't use a indirect cylinder as a buffer cylinder

Too many pumps on the system

Have a look at thermal stores

 

[rpm]

I`ve no idea if it will help or not but look at how people use stoves on boats.

 

[Mack5]

Sorry but can't use a indirect cylinder as a buffer cylinder

Too many pumps on the system

Have a look at thermal stores

In my post I say I don't know where to put a circulating pump? The diagram is my options, I don't know if that wasn't clear or not.

Wouldn't the direct cylinder in the loft be the buffer cylinder? The indirect is for dhw?

As stated in post on a very tight budget, thermal stores are not viable.

Thanks

 

[Best]

What is the buffer cylinder in your drawing actually for?
And note that the f&e tank and the cwt need to be much higher than the cylinder in loft and the vents need to be much higher again than the f&e tank and cwt.
Why not have an indirect cylinder on fitted on upper floor (not loft) and pipe to that?
You could have a cylinder with an extra coil suitable for solar should you wish to do that later.

 

[Mack5]

What is the buffer cylinder in your drawing actually for?
And note that the f&e tank and the cwt need to be much higher than the cylinder in loft and the vents need to be much higher again than the f&e tank and cwt.
Why not have an indirect cylinder on fitted on upper floor (not loft) and pipe to that?
You could have a cylinder with an extra coil suitable for solar should you wish to do that later.

Ah, I should've said. The buffer in theory is to hold enough heat to run a boost circulation round the rads in the morning. I don't know whether I could include the boiler in this circulation, or if have to bridge between radiator return and feed pipes.

I'm in a single storey bungalow, currently the CWS is mounted roughly 2 metres above loft height on rafters. Surely this position wouldn't need to change as I'm not altering the dwh system?

Would the f+e tank be OK mounted at the same level?

TBH the indirect cylinder in the loft would be perfect, but I don't think I could afford to lose the CWS head height.

Cheers

 

[Best]

The bottom of the cwt would need to be well above the height of a cylinder.
The f&e tank would be fine If above any heating pipes or radiators that might be in loft.
The heating vent needs to have enough vertical height above the f&e tank

 

[Ric2013]

Okay, so make that circulation to the direct cylinder a gravity loop. So far so good. As far as I'm aware, this should be in 28mm for safety reasons, but I'll leave that to your plumber.

Pump 3 might restrict the gravity flow so I'm not sure that would comply with legislation/be safe as it theoretically could slow the gravity, even though I expect it would still work. Don't use pump valves!

If that direct cylinder is lagged, which it needs to be to act as a buffer, then you also will need a heat leak radiator to run on gravity, 22mm pipe.

If you must go for a semi-gravity design, then have you considered the use of an injector tee on the heating loop to accelerate the flow on the gravity?

Who's to say pump 2 won't just drag water back through the rads?

My inclination would be to run the rads and DHW coil from the direct cylinder as if it were a thermal store, and use a straightforward S plan arrangement and the return from pump 1 I would be put back straight into the direct cylinder to avoid the risk of the water circulating in undesired ways. Two valves, one pump. Simpler, eh?

The F & E needs to be suited to hot water. Most plastic F & E cisterns are not suited.

The direct cylinder would be better with a vent. Personally I would just angle the flow pipe up so the cylinder is the highest point and vent off the top of the cylinder otherwise you have no way of venting. Perhaps an AAV on the pipe from the top might be considered sufficient. Theres a niggle that says that the cylinder must be vented to be safe, but I think when I consider the rationale, it probably doesn't really need one because it is direct and vented through the primaries (he says thinking out loud).

Why are you feeding the F&E from the CWSC?

How big is this direct cylinder? Even if you get it up to 80C and it's still 70C in the morning, if it's only 115l, that will fill your radiators with hot water, but not for very long.

To be honest, I've toyed with this sort of setup for my own house, to allow my gas boiler to run in tandem with my proposed stove, when I get around to it, and I started to think a thermal store wasn't much more expensive, but then I'd factored in a heat exchanger instead of using one cylinder to heat another.

That said, I wouldn't bother with your version myself, because until your direct cylinder is heated through, you won't be able to start making serious inroads into getting your DHW hot, by which time you may find the stove is producing too much ambient heat to warrant firing it any longer.

You must have a hell of a stove to run 6 radiators. What stove have you? Or are you thinking of only running a radiator or two at any one time?

 

[Welder]

6KW won't do all of that. You'll heat a few rads at a time at best OR the HW.

Personally, I get a heat calc done to see what your proper needs are rather than guessing. You cannot f around with a boiler stove cos if you or your plumber gets it wrong then you'll be sitting atop a literal bomb.

Few plumbers have the experience to work with these. For example, your F&E MUST be a galvanised tank far larger than the std 4 gallon jobbie.

Please take my advice and find a plumber who's both qualified and experienced at stove boilers. Doing this on a shoestring may kill you.

 

[quality]

Sorry but can't use a indirect cylinder as a buffer cylinder

Can you explain why not?

 

[ShaunCorbs]

Can you explain why not?

Cylinders not rated for gravity circuits

Cylinder isn't rated / spec for use as buffer

Really you don't want the coil in as you won't get decent separation eg when system is upto temp etc

 

[quality]

in the application thats drawn it would be poor

Cylinders not rated for gravity circuits, That is not true for all indirect cylinders

Cylinder isn't rated / spec for use as buffer, That doesn't matter as pressure and temp would be suitable for any cylinder

Really you don't want the coil in as you won't get decent separation eg when system is upto temp etc, I agree on this

 

[Mack5]

Some good replies here, firstly safety is my priority. I have a wife and child at home 24/7. I won't take any risks to save money.

If you must go for a semi-gravity design, then have you considered the use of an injector tee on the heating loop to accelerate the flow on the gravity?

Not really sure what an injector tee is, but if that's what recommended then sure.

Who's to say pump 2 won't just drag water back through the rads? Good point.

My inclination would be to run the rads and DHW coil from the direct cylinder as if it were a thermal store, and use a straightforward S plan arrangement and the return from pump 1 I would be put back straight into the direct cylinder to avoid the risk of the water circulating in undesired ways. Two valves, one pump. Simpler, eh? Yep. I cannot remember how many ports are on my direct tank, but that definitely makes more sense. Keeps the gravity return loop cleaner too.

Why are you feeding the F&E from the CWSC?

Mainly as I've seen a couple system's done this way, by way of a ballcock valve. What would you recommend?

How big is this direct cylinder? Even if you get it up to 80C and it's still 70C in the morning, if it's only 115l, that will fill your radiators with hot water, but not for very long. Yea, I did have that concern, it probably is only 115l, its whether the hassle of fitting will be rewarded.

Tbh I'd be happy if it only fed half the radiators for an hour in the morning just to take the chill of the bedrooms and living room. The house is reasonably insulated so is never really cold.

You must have a hell of a stove to run 6 radiators. What stove have you? Or are you thinking of only running a radiator or two at any one time?

I have a hunter herald 8. The 6kw I quoted I believe is wrong, as they do a clip in and a wraparound boiler. The clip in being lower. Ive had another look and the output to water is potentially 8.5kw. It has some mixed reviews, so I am a bit anxious as to how it compares to the 6kw heat only stove for ease of use and heat output.

Personally, I get a heat calc done to see what your proper needs are rather than guessing. You cannot f around with a boiler stove cos if you or your plumber gets it wrong then you'll be sitting atop a literal bomb. Yep I gather that. Since I've been looking into this I've started to grasp how complex plumbing is. I have done my own BTU room calculations through using an online calculator, I will attach it for reference.

Few plumbers have the experience to work with these. For example, your F&E MUST be a galvanised tank far larger than the std 4 gallon jobbie. Will do some digging on this. I wasn't aware.

Please take my advice and find a plumber who's both qualified and experienced at stove boilers. Doing this on a shoestring may kill you. My attitude when it comes to hiring tradesmen is to get as many quotes as possible and pick one about the middle of the road. Unless they've been recommended. I'm from a rural area so I expect there are a few good plumbers experienced in this subject around.

Thanks all.

 

[Best]

BTU calculations look very low.

 

[Best]

Albion Mainsflow direct cylinder (not the combination version), or similar in other brands, will just do the job and with only one pump needed (for to rads). Basically a thermal store.
Heating system water direct into cylinder full volume (so large store for space heating) and a coil for mains hot water.
I don’t like them, and they are overpriced, but that idea gives you one unit supplying hot water and heating, as with other thermal stores.
Still requires heat leak rads

 

[Ric2013]

Why are you feeding the F&E from the CWSC?

Mainly as I've seen a couple system's done this way, by way of a ballcock valve. What would you recommend?

Feeding it from the mains by way of a ballcock valve. Just easier, and will fill more quickly when you commission the system.

Can I make some clarification on the cistern. If used on solid fuel, it must be suited to an uncontrolled heat source solid fuel application. As Dave says, it could be galvanised, but copper is more typical in my experience; you can even get some GRP types that are suited for this application (I didn't believe it either until I saw the manufacturer's data).