Navitron Renewable Energy and Sustainability Forum

BIOMASS => Solids: eg. Wood/Woodchips/Pellets/Sawdust => Topic started by: dtl on June 13, 2020, 09:50:53 AM



Title: condensing oil boiler and boiler stove
Post by: dtl on June 13, 2020, 09:50:53 AM
Hi,

Hi our set up consists of a 20kW (ish) solid fuel boiler stove in the kitchen and a central heating oil boiler situated in an out building.

The boiler stove was added to the existing central heating system about 10 years ago, it is a simple arrangement which is just teed into central heating via a couple of isolation valves on the heating circuit and a thermograravity vent to hot water tank.

The solid fuel boiler has its own pump which is switched on when the stove is used.
There is no neutraliser or similar in the system.
The system works well.

Our central heating oil boiler is about 40 years old and now need replaced having started to leak from its welded seams.

My question is given that the new central heating oil boiler will be a condensing boiler will the operation on the solid fuel stove in any way be bad for it:

ie, usually what happens is that central heating has brought/is bringing the house up to temperature with thermostat calling for heat, we then open soild fuel stove valves, turn on pump and then start burning wood in solid fuel stove.

When the central heating thermostat stops calling for heat is OK for warm/hot water to be pumped around a non fired condensing central heating boiler?

Thanks







Title: Re: condensing oil boiler and boiler stove
Post by: Philip R on June 13, 2020, 01:47:34 PM
A system schematic would be useful.
A new condensing boiler needs to be fully pumped. What sort of cylinder do you have. Is is a coil heat exchanger type or a single feed cylinder with the tank air vent type heat exchanger inside?


Title: Re: condensing oil boiler and boiler stove
Post by: dtl on June 13, 2020, 02:05:53 PM
Hi,

The oil central heating boiler has its own pump.

It was a standard oil powered open vented central heating system with hot water via a calorifier pipework in a the domestic hot water tank, with a timer valve that opens to take central heating water around calorifier in hot water tank.

The solid fuel boiler was added by basically teeing into a radiator, adding two manual isolation valves and a separate pump.

Two safety thermocirculation lines were added from solid fuel stove to existing hot water tank by teeing into calorifier pipework where it entered and exited the hot water tank,

Thanks

Thanks


Title: Re: condensing oil boiler and boiler stove
Post by: kdmnx on June 13, 2020, 02:40:51 PM
Condensing boilers really donít like anything other than perfectly clean water, therefore you need a solution to ensure water water that goes through the wood burner doesnít also go through the boiler. There are a few ways to achieve this depending on your current system design.


Title: Re: condensing oil boiler and boiler stove
Post by: dtl on June 13, 2020, 03:05:51 PM
Thanks for the reply.

Why is the water going through the wood boiler dirtier than elsewehere in the central heating system?

Thanks


Title: Re: condensing oil boiler and boiler stove
Post by: gb484 on June 13, 2020, 04:36:05 PM
Hi, have read your post several times and am still not sure what your concerns are. Corrosion? While I appreciate that your installation has worked well for a number of years, without seeing a system diagram, I would not like to even say that it was safe to use; The mention of isolation valves on a WBS raises alarm bells. Still, was browsing the SALE pages on navitron and saw this: https://www.navitron.org.uk/anti-condensing-recycling-pump-unit, a laddomat, basically, which could be exactly what you need. Hard for me to know, because you do not give enough info. You will have to decide for yourself.


Title: Re: condensing oil boiler and boiler stove
Post by: dtl on June 13, 2020, 05:43:51 PM
Hi,

The isolation valves do not isolate the thermosyphon pipes, the thermosyphon pipes are always open between the wood burning boiler and the domestic hot water tank.

When the woodburning boiler and its pump is running, heated water circulates around the central heating boiler by virtue of the pump on the wood boiler, even though the oil central heating boiler is off.

I know this design is not particularly efficient, however it works fine and at the time of installation it was a compromise around some inefficiency versus taking the place to pieces.

My concern is now switching from a old oil central heating boiler to a modern condensing boiler, and whether this circulation of water would in any way be bad for the condensing boiler,

Thanks


Title: Re: condensing oil boiler and boiler stove
Post by: Alan D on June 13, 2020, 11:02:07 PM
Ref : My concern is now switching from a old oil central heating boiler to a modern condensing boiler, and whether this circulation of water would in any way be bad for the condensing boiler,

The circulating water will not up set the condensing oil boiler. The hotter the water in the boiler when it starts. The better.
The down side is the losses / waste of energy that you have. By circulating water through the boiler you have no control over over the energy being wasted.
Condensing boiler will be more efficient.
It will not last very long.
Condensing boiler on gas. Will last reasonable time. No sulphuric acid in the flue system.
Old oil boiler. Combustion wise not as efficient. Flue system hotter. Sulphuric acid in flue gases condenses further away.
Condensing boiler on oil. More combustion efficient. While starting / getting up to temperature has sulphuric acid in the flue system condensing on internal parts.



Title: Re: condensing oil boiler and boiler stove
Post by: brackwell on June 14, 2020, 07:39:17 AM
And when the oil boiler is off the hot water is going out of the house to keep a oil boiler warm in a out house -are you growing something out there then  ;)

I guess you have considered doing away with the oil boiler altogether and spending the money on reducing the CH demand - yes of course you have.  Most houses these days can run on 20KW.   At the moment with the oil boiler in a out house and 2 sources of heat you have large ineffiences of stop start losses and pipe runs.  What are you doing for hot water?



Title: Re: condensing oil boiler and boiler stove
Post by: Alan D on June 14, 2020, 09:43:13 AM
Ref : It was a standard oil powered open vented central heating system with hot water via a calorifier pipework in a the domestic hot water tank,

If you want to keep it as a second system. Fit a Honeywell motorised valve onto the copper pipe that gets hotter first when heat comes from the other source.
Oil boiler / Oil boiler system circulating pump only starts when you ask the Honeywell valve to open.

Thirty five years ago I fitted a Honeywell motor removed from a motorised valve and a home made mechanical flue damper to my old oil boiler. the boiler only started
when the flue damper was driven to the open position and a cam micro switch proved it was in the open position. Every time the boiler went off on the temperature limit
statt the flue damper closed. I also fitted lots more insulation all around the boiler.
Why did boiler makers not think of saving vast amounts of heat with a simple motorised damper. ??  :hysteria

I have repaired very large Industrial steam / water boilers for 40 years.
Some of the old rivited ones with asbestos all over them had very little repairs in there life time. 40 years plus.
Some of the old ones with J Prepp internal tubes had very little repairs in there life time.
Oil fired boilers with expanded tubes had very little repairs in there life time.
The failures started when Natural gas came along. The temperature at the rear of the furnace tube is a lot hotter.

Then the Chinease / Made of metal ????? ones came along. Weld repairs started on a yearly basis.
No condensing one for me. House boiler thirty years old without repair.



Title: Re: condensing oil boiler and boiler stove
Post by: dtl on June 14, 2020, 10:04:50 AM
OK thanks for the good ideas.

The boiler that is about to be replaced is approx. 40 years old, so I guess I cant complain too much.


Title: Re: condensing oil boiler and boiler stove
Post by: Countrypaul on June 14, 2020, 12:46:34 PM
You might be able to pickup a boiler similar to the one you have on Eblag for next to nothing as they have little real value, that might give you another 10 yrs (longer than many condensing boilers I've heard about) without having to make any major changes. You could then invest teh money you've saved up in more insulation.

Just out of curiosity, where is the outbuilding in comparison to the house?


Title: Re: condensing oil boiler and boiler stove
Post by: Philip R on June 14, 2020, 12:48:26 PM
Couple of additional points;
Modern kerosene 28s oil is very low sulphur conent, so the exhaust condensate is lower acidity. So long as the main combustion chamber gets hot enough quickly, not too much condensation will linger in there and reduce corrosion of the mild steel surfaces. The condensing section is stainless steel and the flues/drains are plastic, so no corrosion there. Just avoid the boilers with tacky condenser units fastenned by riv nuts or pressed in fasteners ( Worster Botch). Go for something welded on properly like a Grant.

Your old boiler sounds like it had an open flue. Did the burner have an air damper that was oil jack driven? If it did not and had just the standard air inlet, there would have been a draft of air taking heat out the boiler and up the chimney, but it would have been keep dry.
All modern domestic condensing oil boilers generally have a more low level flue arrangement so convection draft losses are reduced. Also the higher resistance to air flow of the heat exchangers and condensing section reduces drafts also.
When you fit a new boiler, you may want to flush the system, but be aware, the clag might be making it watertight, flush it and leaks might arise.Otherwise as a minimum, fit a magnetic filter to the boiler return to collect magnetic debris at least, especially if system has a feed and expansion cistern in the attic. Also clean out the clag in there to when changing the boiler. That is were you can find microbial gloop, where new life forms may be found.
Philip R


Title: Re: condensing oil boiler and boiler stove
Post by: dtl on June 15, 2020, 11:07:06 AM
Hi,

The oil boiler is in an outhouse about 10 meters from the backdoor of house.

The pipes run underground in a soil pipe packed with insulation.

The wood boiler is at the far side of the house 25 meters from oil boiler, which is why it was going to be hard to fit a neutraliser thing without pulling the place to pieces, when the wood boiler was added ten years ago.

There is no automatic dampners or anything on the the oil burner, open all the way through to flue.

I just cleaned out my header tank and you are correct, it was full of horrible stuff.

I am scared of a powerflush, but as you suggest I will fit one of the system filters,

Thanks




Title: Re: condensing oil boiler and boiler stove
Post by: Alan D on June 15, 2020, 12:38:25 PM
Ref : The oil boiler is in an outhouse about 10 meters from the backdoor of house.

Fit the motorised valve on the flow pipe before it leaves the house.
Oil boiler / pump starts only when the motorised valve is open.
Is the outhouse big enough to store a few more spare condensing boilers.


Title: Re: condensing oil boiler and boiler stove
Post by: dtl on June 15, 2020, 02:04:09 PM
Hi,

It would be a bit more hassle to get at the pipework within the house, since I would have to pull up some flooring.

Given the valve is stopping the flow is it not just as good being located in the outhouse?

Yes plenty of space in the outhouse,

Thanks