Open wood fires -improving efficiency

MilesG Image
11/20/2012 - 13:48

Anyone come across a 'serpentino' for improving the efficiency of an open fire? Basically a coiled metal tube with a fan which draws in cold air which the serpentino warms and convects back into the room. The logs or coal sit on top of the tubing & the efficiency goes up from 20% ish to over 50. A work colleague reckons Obi used to sell them. Can't install a stufa as the house is rented . The mains gas boiler is good but v expensive to run. They are available in USA for $500 but cost the same to ship (then iVA etc on top)



Here s the link. e I emailed the company and hence the shipping quote of $500 to Italy. I ve found nothing similar in Italy or UK -yet!

THe problem with open fires is quite simply that the heat goes directly up the chimney (and often the smoke comes into the room). The solution to this is to use a Jetmaster cast iron box.  Esentially it's double skinned steel box which allows a natural convection of the heated hot air into the room but the front is still completely open.  They're quite expensive - £1,500 to £2,000 but I have just bought one on eBay for £130.  There is only one moving part - the lever for the vent so they can and do last for decades.  No need to buy one new. THe efficiency is about 45-50% as compared to a stove which might have efficiency of up to 85% - but you do have a wonderful open fire. They do tend to heat the room faster than a stove as well. They are made in the UK and there are are stockists in France and Belguim - but my advice is to buy one second-hand and have it delivered out.  THere is also another make called Tortoise but I have not use one of those.  Same principle however Anyway whatever you choose, good luck!

I don't have experience of this kit specifically but I'd doubt if it would be worth your while spending too much trying it because: 1/. The tubes are small and trying to remove heat with air as a medium so you are probably looking at extracting about 0.5kW. I say this because with a much bigger back boiler full of water on my Clearview 650 stove I am only getting something like 2kW. 2/. You should consider that if you remove heat from a fire that the efficiency goes DOWN because the lower temperature may not enable some of the heavier creosote type combustibles to burn.  What you could do though, for a lot less, is to get some shiney stainless steel walls made for the fire to reflect heat into the fire and back at you to give better thermal efficiency and extracted heat via radiation.  I once transformed an industial gas oven just by lining the floor with kitchen foil.  If you really want to do the grate thing then why not just make one out of gas barrel fittings - sealed or welded to make sure you don't gas yourself - and give it a trial blow through with a hair dryer on cold. A fun project for about €30 - please report back. Now you have liberated the €1,000 you can buy lots more wood.  Finally about efficiency claims: as open fires can become negatively efficient then ANY heat extracted can produce any amount of efficiency claims you care to print.

Sagraiasolar..thanks for the info.Can you please give a few more details regarding gas barrel diy job. Can get welding etc done and will report back to ....hopefully!! Thanks again,Paul

In reply to by Spud

What you do is go to the plumbers and get those heavy steel pipe fittings. With lots of T's, elbows and nipples you can assemble the shape you want. You will need to overlay 2 comb like assemblies together if you want a close pitch between the grate pipes.  No need to weld or seal at all if you are blowing the air into the manifolds. 1/2" bsp might be the size to allow for more branches. You'll find the air coming out will be very hot.

In reply to by sagraiasolar

Sagraisolar..As usual with these things,haven't got round to it yet!! You've just given me a kick up the backside to try it.As opposed to the serpentine,we are making five upright "C" shaped one inch threaded pipe(to make smaller diameter at one end) Do not know if 5 individual pipes would be less efficient than one single serpentine.Just a lot easier to try for first attempt,plus it's for a bit of fun anyway.There are also quite a few Jetmasters keep cropping up on ebay around £100-200,just waiting for one with the right dimensions.Will try both and again will keep you posted.Not back in Italy until June,so should be fun testing them in 40 degrees heat!! Thanks again for the info..

Thanks again for the info,much appreciated.Will let you know what the outcome is.Not sure if I'm being a bit daft or not but what do we use for the "blowing" bit...Kind regards, before,can do all welding etc,just not sure about blowing air into manifolds etc etc

I've definitely seen these things in OBI - a few years ago. The 'pipes' which formed something which looks like a log basket were about 35mm diam. The key word is definitely serpentino. Never used one! I do endorse the recommendation for Jetmasters - they are almost (well, about half way) as good as a closed stove but look miles better- I think they originated in South Africa, but maybe they now make them in the UK.

Thanks for everybody's help and advice - much appreciated. The 'grate heater' option ie pipes sounds as though without a blower pushing cold air through the pipes, the system is not very efficient. There needs to be a big temperature difference between inlet and outlet to create a flow, and as the pipes heat, the difference reduces to nil, allegedly - hence the need for a fan, which can be noisy according to some users. As all devices, Jetmasters or grate heaters, would need to be shipped, making them v costly, the option of splitting the cost of a woodburner and its installation with the landlord (if he goes for it!) is looking more attractive, especially as they are very efficient and available locally. However, I'm not giving up on this yet, and do like the idea of constructing a grate heater out of gas pipes - cheap and relatively easy if you use threaded joints rather than welds

In reply to by MilesG

Couldn't you just bung in a small stove with a  bit of pipe, closing the opening above the stove with a lash up involving angle irons (if there isn't a convenient shelf) and a few extruded clay tavellone? Then you just take the stove away with you when you leave!

I gave up on trying to source a serpentino or make one, so have ordered one from Cost shipped is US$800, I reckon 2.7% import duty & 21% IVA on top. Should arrive in a couple of weeks & I ll post details of how effective it is & the final cost. I tried to get the proprietario to agree to pay the cost of installing a wood burner if we paid for the burner but he wasn't interested. At least this fireplace blower and tube system requires no special installation & we can take it with us when we go. 

Had a quick look at the Tifon website but it seems they are all complete fireplace/grate arrangements. Yes it is 110volts so needs a step down transformer - they can be bought from Maplins in UK for £15 to £20, in Italy they are probably available, esp at US bases like Vicenza or Camp Darby... if you can get to a PX.

"Yes it is 110volts so needs a step down transformer - they can be bought from Maplins in UK for £15 to £20, in Italy they are probably available ......." If you can't readily find a step down transformer, as a [temporary?] measure I suppose you could always buy an electric shaver point [110V/220V] and wall mounting box, wire it to a plug and use the 110V output to power the American sepentino

We just installed a 9kw insert stove in our kitchen where the open fire was. We popped in a  a 6inch inox liner and raised the chimney a couple of metres. No smoke in the kitchen and at least  three times as much heat output than the old fire on half the wood!!! The new thing has a wee electric fan, and actually warms up the whole house to a reasonable level. However the hard work installing the trioso super 10 insulation and drylining the ceilings has made a huge difference.

After a faff with the Maplins 110V transformer not working & having to order another, the blower from Woodland Direct is in the hearth and proving much more efficient at heating the large main living area in our house than the original open fire. Even without the 2 speed fan, if the fire is hot enough, the pipes kick out a warm air flow into the room rather then just up the chimney. If I could work out how to ,I'd upload a photo. Required absolutely no modification to the existing fireplace.   Not a cheap option (altho a lot cheaper than a woodburner installation). i'll let you know how it performs as/when we have sub zero temps outside..........