Fireplace Home Heating

Yes, this has been done before. But to my knowledge this approach is no longer being pursued. There's no reason (that I can see) that this cannot be successfully done again. But you will have to mitigate more of the risks than earlier companies did to produce a successful product. Boiling contained water with a tricky to regulate wood burner can and will become a problem.

the monoflow system uses a closed loop and installs a fitting that diverts some of the flow up through the floor, through the radiator, and down into the return side of the same fitting where there is a nozzle that has a venturi effect. The water needs a certain speed in order for the rads the get water and there needs to be zero air in this system, which usually has a higher level water tank with 10-20 feet of head. They are not otherwise pressurized.

search monoflow and get a sea of links.

here is one

http://www.bellgossett.com/Press/BG-monoflo.asp

Sounds like the old back boiler system that was pretty standard in the UK for a long while.

Nice but most of your heat is going up the chimney with the air that is drawn into your room from OUTSIDE which is why people in front of real fires have cold backs. The 'swede's, I think, use a air duct into the grate from outside. Room gets the full benefit of the radiated heat and NO draughts (and thirty percent less Fuel). Do it nicely and you should be able to take ash away from outside too, saving on carpet cleaning etc. Car thermostat sounds good but they do fail. A deliberately weak pipe would protect against boiling water/steam escaping uncontrolled. Siting a temperature sensitive protection is also an issue, you have to be sure it's as hot as the water in the 'boiler'. The 1900's back boiler had a flap at the back of the fire, almost at grate level, so hot air from the fire could be diverted through a cast iron boiler linked to an open to air hot water tank. When gas boilers came along this system continued as most were retrofit installations. Modern mains pressure water heaters have electronics to control water temperature. Several babies have been killed (UK) by these electronics failing, the hot water tank boiling and finally failing spilling boiling water into the loft, and then to the bedrooms below. Children and adults escape quickly, babies aren't able to. Take care, be safe. It is NOW law that new installations have an overflow from an open to air header tank. Victorians 1, Legislation 0.

The 'swede's, I think, use a air duct into the grate from outside

You've reminded me that someone I know in the UK self-built a wood frame house a few years back. They used this duct system controlled by a sliding grate beside the fire & have found it to be very successful.

I believe that a sub-floor system is among the best methods for heating. I formed that opinion almost 50 years ago when we didn't have the same level of materials and regulating devices available today.

The primary distinction between what you are proposing and a conventional baseboard heating system is not that yours is under the floor; it's in the fact that a furnace can be turned off and on at will. Wood and pellet fireplaces can not.

I see no reason why the temperature and regulatory devices from a hot water baseboard system can't be used to divert surplus energy to an insulated holding tank.

You need some method for controlling the temperature in the room. You just can't continue to pump captured heat into the floor.

You will also want to know how much thermal energy is being captured in the fireplace at any given moment so the volume of water needed can be properly calculated for the sub-floor circuit(s) as well as the water in the capture tank.

You have no really absolute method for telling the fireplace "enough!" so you need to run some tests and do your math.

The plumbing for the fireplace has to be carefully designed and built. Not surprisingly, most if the heat is not under the fire but above it in the tapered section leading to the chimney. I found this out the hard way when I naively attempted a forced hot air system made of 15 parallel sections of 2" electrical conduit, each bent and welded to form a large letter "C". The nest of pipes was placed into the fireplace with the back of the "C" up against the rear fire brick.

A manifold forced air into lower part of the "C"'s and captured heat from a fire inside the "C". Did it work? Yes but not nearly as good as I hoped for. In fact, I suspect I generated more heat welding the system then it ever captured! I did some surface are calculations and saw immediately that what the system needed was more surface area, fins actually, to capture more heat from the flames. Yours will likely need them too.

Yours will work better as the specific heat of water is better than air but you'll still need surface area and a pump, not just to raise the water in the heat exchanger but to regulate how long it's in there capturing energy.

Variable speed motors are not to be found in 120 VAC single phase so you will need a 3 phase 220 VAC motor driven by a 220 single to 220 three phase solid state inverter. They are not expensive but cost enough that you will probably find it simpler and less costly to simply turn the motor on and off and regulate flow that way.

Up until recently, sub-floor heating system coils had to be chosen before the house was built and put in place prior to pouring the cement slab for the first floor. Sub-flooring heating coils kits made for under wood floors can now be had as aftermarket installations specifically for wood framed homes and are especially appreciated for use in the upper floors of multistory buildings.

This is not a difficult system to design or build but it is time consuming and, if it's typical of other projects, it will need to be debugged, tested and debugged some more. If you can find someone who has done it, you can profit from their mistakes.

Walking about in socks on a warm floor and the uniform way in which the room is heated is a treat worth pursuing

My only caveats are that 1, you don't spend more time and money building it than the value of the energy captured and 2. keep it simple. Problems develop exponentially as a function of complexity.

Good luck

L.J.

Nicely done, you get a GA from me for it. Particularly for the combined ideas of "keeping it simple" and expect problems that will need multiple iterations.

I personally do not like underfloor central heating as it is too slow to react to changes in the outside temperature, like often 2 days or more.....

You need radiators for quick heating when the weather is changeable.....then why bother with the floor....?

Also, as already mentioned, it needs to be installed while building the house, its a hell of a job to do later.....

Pellets burners are very quick to switch off and on (not slow as somebody else mentioned!!), not as fast as gas or oil but VERY close.....also, for the heat produced, very cheap to run.....

I personally would design a system that connected to a normal closed central heating circuit, with an extra pump just for the fire, to allow the heat from the fire to "add" to that of the central heating system. If the fire was good, this would tend to turn off the central heating boiler and save money at the same time.....

Warning thermostats would be a good idea......as would radiators instead of underfloor.....make the rads big (mine are approximately 4x bigger than a plumber would install, this allows you to get a good heating effect from cooler (safer) water temps. Keep water temp to below 60°C, less would be better. I run with around 50°C on really cold days, less when its a bit warmer.....also the house is really well insulated!!!

Keep us informed how it goes......

Around 7 years ago I designed and built my own wood burning boiler system that heats my house. Its located out in the side room of my shop. Its a full water jacket dual pass flue design with outstanding efficiency. I went with a simple surge tank and open system design. There is no practical way for it to build up pressure that way. The mess is outside and it heats the house with a simple heat exchanger that sits under the furnace. No insurance premiums or hassles either!

Its not complicated however it is very very time consuming to build such a system. I am a metal fabricator and electronics/electrical service tech by trade and I can tell you its still a lot of work to set one up properly. Granted if done right its well worth the savings in fuel. I figure I have spent around $3500 building and installing my system and it has saved me about $17000 in fuel costs in 7 years.

However its all digitally controlled off of a commercial PLR system I designed for it and intergrated with a digital smart thermostat in the house. It has multiple fail safes built in and is basically a start a fire and push a button operating system. Everything else is automatic. I just load it up once or twice a day and clean out the ashes every two or three days.

To replicate it and install one again would be around 150 - 200 man hours of work and thats with knowing what I am doing now.

If your designing your own house heat system do it up right the firs time. Make sure you have the correct and adequate types of materials and layout in place. Possibly consider that you may go to an outdoor boiler system in the future as well. Doing up the house heating system right the first time will save you piles of time and money later when you upgrade the design.

From the previous posts you may have learnt, that in pronciple it is possible to "extract" heat from the fireplace and feed it into a hydronic heating system. I live in Germany and over here, such systems become more and mor common. In most cases the consist of a wood burnng stove (or fireplace) and a so called "waterpocket" (??, don't know if that is the right translation, my dictionary failed to give me any better wording). That is the easy part of the excercise. The crucial thing is saftey! You should install a safety device, that will prevent evaporation of the water contained in the system under all possible operation and likely failure conditions, and I am sorry, your thermostat from your car radiator will not do the job! You must prevent the forming of vapour in the system as this will lead to a rapid increase in system pressure, potentially resulting in sudden rupture of your pipework and / or water vessel. I guess you can imagine how destructive the consequences might be. I remember that such a hazard was reported from Austria about one year ago. several people were killed, their ski hut blown up, just because the had shut the water circulation, a vapour bubble formed and disruted the pipes. - So please be careful when you build and start-up your system!

regards nudnik

I believe in the UK we would call such a unit a "Boiler" (though it should never Boil!!!)

What is the German word for such a unit? Wassertasche??

They are still very popular over there (UK) I believe.....and from my childhood, my memories are that we had actually two of them, one in the kitchen and one in the lounge fire, we were never short of hot water in the winter time.......

Today, there would be also a large insulated storage tank, so that even after the fire had burnt down at night, the heating would still have a source of hot water to call upon......modern!!

Hi Andy,

Yes, you are right. The German expression is "Wassertasche". basically this is the heat exchanger in the stove. I believe the thing you are referring to is "Wasserschiff". This is a (large or small) kind of kettle or boiler, where water is heated and kept hot for typical use in the kitchen, like dish washing, cleaning and so on. The "Wassertasche" is intended to take up the heat from the fireplace and route it to a (hopefully insulated) hot water storage from which it is fed into the hydronic heating system - and, you are right, the hot water storage acts as a buffer system to supply the heating system with hot water even after the fire has burnt down.

From your translation I assume that you are quite familiar with German :-)) If you wish to get more information, you could go to www.haustechnikdialog.de and search for the terms "Kaminofen" and "Wassertasche".

(sorry, but I do not know how to correctly translate these specific terms into English! I could not find a suitable dictionary until now. Any suggestions? )

Cheers nudnik

No thats not correct, what you are referring to is a "Kettle" in English, also its not one of those funny things you see on the wall in older German kitchens, to heat water for tea or coffee......

The boiler I am talking about (in my youth 50 years ago) was made of heavy cast iron and sat at the back of the fire (unseen), and was permanently plumbed into the house water system

The ones we had then heated the house hot water directly, something that would not probably be done nowadays, dangers of "furring up" in hard water areas.....

It was a very cheap bit of kit then and if it needed replacing after 10 years, then who cares.....

Hi Andy,

Yes you are right, the boiler built into the stove for preparation of hot water (plumbed to the water system) is the so called "Wasserschiff" (- and no, I will not literally translate this expression into English as that would cause far too much confusion ). I do also remember those systems in old stoves which supplied a hot water heating system in the house, water circulation depending on natural convection only! Although we did not have it in our home, a friend's parents had such a thing.

Thank you anyway for helping me to sort things out. As I am not a native speaker it is often a bit of an effort to describe things instead of using the correct wording . Promise, I am trying to improve.

Take care, nudnik

I live in Germany since '81, still find some occasional words that I have never seen before.....its normal business.....

Nice to know you, stay in touch.