Author Topic: Heating with wood options  (Read 8022 times)

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aguillar

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Heating with wood options
« on: November 20, 2007, 12:28:31 PM »
Position: converting a timber and stone barn to a house, 100mm polyurethane in walls, 140mm in pitched roof, 250mm rock wool in floor, target ventilation rate 0.6 air changes/hr. Fair bit of thermal mass using slate flooring and heraklith in walls. 120m2 floor area. Location on edges of England and Wales nr Ludlow. 2 residents. Off grid, installing a Proven 2.5 soon, estimated average wind speed 4m/s. 2x1m solar water heater [most likely flat panel with 12v PV pump]


Option 1; Underfloor heating running off a wood burning stove with back boiler.

Think we need an accumulator and pumps - concerned that pumps may require too much electricity given we are not on the mains and don't yet know how good a wind site we have here.


Option 2; Pumped radiators running off a wood burning stove with back boiler.

Don't need an accumulator but still need a pump, same concern with electrical requirement.


Option 3; Thermosyphoning radiators running off a wood burning stove with back boiler.

No pumps required but due to restrictions on all pipes [min 28mm copper] needing to rise along their entire length from boiler to radiators it is not possible to have radiators in some rooms without pipes crossing in front of windows a few feet up and having a couple of radiators half way up the walls..


Option 4; Two wood burning stoves without radiators [well one would have a back boiler for heating domestic hot water and would have a radiator for pressure relief]

Nice and simple to install but will the heat percolate through the rooms enough? Building regs require us to put sound insulation in the internal walls and we are worried that this could prevent heat moving from heated rooms to unheated rooms.


Any comments/ suggestions very gratefully received!

« Last Edit: November 20, 2007, 12:28:31 PM by (unknown) »

ghurd

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Re: Heating with wood options
« Reply #1 on: November 20, 2007, 08:48:41 AM »
"Any comments/ suggestions very gratefully received!"

Remember you asked for it.


I have been thinking about this a lot lately and would go with #1. No question.


The pumps don't use much power, maybe 10 or 20W, and they don't run 24/7.


Stray thoughts...


Those days when the temperature isn't too cold, the floor will be warm. Might not need a fire that day.


Could use 2 smaller pumps and 2 thermostats.  One pair set at say 70F/21C, the other set at say 68F/20C.  I believe it would be more efficient, but if 1 pump couldn't keep up on cold days, the other would come on.  Plus if one quit, there is still one that works.


Could run an extra seperate line in the floor for solar.  Fairly cheap. Not sure if that was the plan.

Here, when it starts getting cool, we still have quite a few sunny days left to come.  Could certainly postpone the heating season a while.

Plus it could give a jump start on heating the ground.  I wondered about solar heat pipes a considerable distance below the regular pipes, then start the solar heating season a week or 2 or 3 early.  Heat all that 55F/12C dirt up a bit when the free BTUs are available.


Could thermosyphon, at least some, in a 3rd seperate pipe.  I know it would work.

Some local people heat domestic hot water with a small wood/coal/kero heater in summer.  

In winter they use the home heating system for domestic hot water, however it makes for some water temperature issues.  They manually partially open a valve if the water temperature gets a little to high. The colder it is outside, the more they open the valve, because the more heat the stove is making.  The valve feeds a thermosyphoning loop with about 8 to 16' of copper pipe with press fitted aluminum washers (like the guts of a radiator, and usually placed under the bathroom floor) which removes enough heat from the system to keep the safety valve shut.

The water returning to the heater is still VERY hot.

Open a valve to a small radiator considerably higher than the heater, then drop it down into the floor pipe, then back to the heater.  The beauty of that is it runs 24/7 without power.  It would not usually keep up and manual control is probably best, but whatever flow it makes keeps the pumps from running the same amount. I believe it could be considerable.

Another benefit would be moving heat to the areas of the house far from the wood stove. Run the thermosyphoning pipe to the other end of the house before making loops (maybe even lightly insulate the run to the loops?). The areas near the stove already get heat from the stove.


Could, I think, use all the primary pipes with 2 staged pumps. It would lower the head due to friction (less battery amps) with only one pump running, at almost no additional cost.

I'm not sure, but expect most pumps have considerable resistance to reverse flow. If not, use a check valve.  Maybe a horizontal check valve placed verticially would work with a lot less drag.


Be aware the controls for DC are not readily available (in the US).  They are not hard, complicated, or expensive to make, but I couldn't buy them off the shelf.  DC is far better than an inverter, so start looking at design parameters now.


What I recently did, though if it was for personal use I would have made something 100% solid-state, thermistor controlled, and 12V.  

I didn't mention the 2nd thermostat measured if the stove was burning or not, because if the stove was NOT burning it prevented the pumps from running (wasting battery power if no heat was available).

http://www.fieldlines.com/story/2007/11/5/15930/5940


This is a coal fired water heater using thermosyphoning to a standard 40 gallon HW heater used only as a holding tank (behind the wall).  Takes about 10~15 minutes from dead cold to plenty too hot for a shower.

It would do a much more efficent job heating the house in cool temperatures than the giant gravity-air thing (almost shown) on the right. They must often open windows while 32F/0C outside.

http://www.otherpower.com/images/scimages/2050/watrheatr.jpg


I'd suggest running a few 'extra' pipes in the floor too.  Cheap to do. Adds options later.

G-

« Last Edit: November 20, 2007, 08:48:41 AM by ghurd »
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Stonebrain

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Re: Heating with wood options
« Reply #2 on: November 20, 2007, 02:10:49 PM »
I surely would opt for option 4.

And even I would try to place the boiler above and as close as possible to the boilerstove,so it can work by thermosiphon.That's good for your wallet and for the planet.Low technologie.No need for electricity.But you need a good solarwaterheater for the summer (that's difficult withou a pump because most often you put a panel on the roof).


Ok,the kids will sometimes have to put a pull when they do their homework in their room.But that's what I had to do when I was a kid and it never has hurt me.And with a good exterior isolation,the situation will be much better than in the old days.to put your computer.For sleeping you don't need and even want the same t° as for the livingroom and in the badroom,if you have a warm shower you can do with a somewat lower t°. Just choose a good place for the computer.


cheers,

stonebrain

« Last Edit: November 20, 2007, 02:10:49 PM by Stonebrain »

feral air

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Re: Heating with wood options
« Reply #3 on: November 20, 2007, 03:01:50 PM »
Quick thoughts...


Radiant floor heating is very very nice. It should be mandatory (kidding) for any rooms with linoleum, hardwood or tile floors. Happy feet=happy people. ;-)


A stirling fan is a good way to move the heat around without electricity. I plan to get one as a family-gift for xmas since they're like $170 or so. I've been thinking I might try to use the existing duct work under the house to move the heat to the outer rooms with the stirling fan...which might work better than just leaving the bedroom doors open and w/o a fan.


Vents near the ceiling on the inner walls could be an option too. You should be able to pick up several vents cheap enough. The master bedroom in my house has a vent just above the door and it seems to help having it open. Curiously, the other rooms don't have vents..wonder why (fire propagation? though if a room is that engulfed you're pretty much screwed anyway).


I tend to prefer 'simple and fairly effective' over 'complex and perfect'...so you get where I'm coming from. take it easy

« Last Edit: November 20, 2007, 03:01:50 PM by feral air »

Stonebrain

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Re: Heating with wood options
« Reply #4 on: November 20, 2007, 03:21:49 PM »
Being someone who heated most of his life on wood I have my point of view


Heating with wood can be a duty and a pleasure.Putting a stove in a remote area of the house or outside makes the burning a duty and you don't have the pleasure of the fire.

Having the stove in the space where you live gives you the pleasure of the fire and this makes the duty easy.

Specially the modern stoves that has nice window that burns clean are fine and replace even television,another economy.

Placing the stove in the place where you don't need the heat generate extra heatlosses too

A stove needs some attention to open and close the draft.But ok,maybe this can be correct on an automated stove too.


Better spend less money on a very nice and efficient stove than more money on a crappy central heating system.Most stoves have enough heat in the exhaust gasses to put a heat exchanger for water after it.


Well .. that's just my filosofy.


cheers,

stonebrain

« Last Edit: November 20, 2007, 03:21:49 PM by Stonebrain »

jonas302

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Re: Heating with wood options
« Reply #5 on: November 20, 2007, 06:40:29 PM »
Just for info I checked my pump it rates at 92 watts .80 amps 115 volts costs about 100usd it moves the water several hundred feet and then up 20 ft so probly bigger than what you need By the way a pressurized sysyem will require a smaller pump

best of luck

jonas

« Last Edit: November 20, 2007, 06:40:29 PM by jonas302 »

aguillar

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Re: Heating with wood options
« Reply #6 on: November 21, 2007, 09:13:23 AM »
Thanks for all the comments!!

Still learning, more research and questioning to do before we will be able to decide...
« Last Edit: November 21, 2007, 09:13:23 AM by aguillar »

feral air

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Re: Heating with wood options
« Reply #7 on: November 21, 2007, 11:17:01 AM »
Here's where I was going to get the stirling fan. I guess now it's $189 +s/h.


I'm not affiliated with 'em - just thought a direct link would be nice in case you want to check it out too. take it easy

« Last Edit: November 21, 2007, 11:17:01 AM by feral air »

ghurd

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Re: Heating with wood options
« Reply #8 on: November 21, 2007, 12:38:51 PM »
"EcoFan" is only $80~100.  Runs on a Peltier.  99.9% Quiet.

They have a new larger version too.

Looses a bit of the Wow! factor maybe.

G-

« Last Edit: November 21, 2007, 12:38:51 PM by ghurd »
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gale

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Re: Heating with wood options
« Reply #9 on: November 21, 2007, 12:40:04 PM »
     I like option #1- but with a few changes-  use the thermal mass of the barn as heat storage, instead of wool in the floor, how about a thick (300mm+)concrete slab with water pipes inplanted, use the thermanl mass as a heat storage unit. With a outdoor burner, you may only had to burn every other day or posibly much less. A good example is a "russian stove"-  a huge amount of stone, a very small fire box.  you heat it once a day and the stones warm the house for the rest of the day. actually a central located russian stove with mild obstructions ( walls and divisions)could easily heat the structure


     Your insulation in the walls and ceilings in the USA would be extremely thin,  USA would be closer to 166mm in the walls and 350mm in the ceiling.  I understand the England is a much milder climate.  my thoughts are if you don't lose it you do not have to replace it.

« Last Edit: November 21, 2007, 12:40:04 PM by gale »

feral air

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Re: Heating with wood options
« Reply #10 on: November 21, 2007, 06:52:01 PM »
Nearly-free air circulation is neat no matter what tech drives it. Since the EcoFan is half the price (give or take) I think the choice is pretty obvious. Thanks for the heads-up. take it easy
« Last Edit: November 21, 2007, 06:52:01 PM by feral air »

hydrosun

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Re: Heating with wood options
« Reply #11 on: November 21, 2007, 10:13:45 PM »
I'm able to move the heat from the stove 40 feet using only thermosyphon. I made many zig zag pipes of 1/2 inch copper and put them on three sides,and the front top, of the outside of the wood stove. They all tee into a 1 inch insulated cpvc pipe that rises from 6 feet to 7 feet above the floor. Then a tee that goes up to the loft and a 55 gallon tank, or along the ceiling of the kitchen through two parrallel 1/2 inch copper pipes. The pipes form two rectangular loops 20 feet long and then back to a 1 inch tee of cpvc pipe and back to the wood stove. I have 2 inch wide strips of reflectix on top of the copper pipes on the ceiling to reflect the radiant heat down to heat people and objects below the ceiling.  I got the idea from a heating system in my daughters apartment that had electric radiant heaters in the ceiling. I did a web search about the details and found that the key was to place insulation and a radiant barrier above the heater.

 Because of the levelness of the copper loop I had to run water through the loop to eliminate air locks in the loop . I  opened the pressure relief valve at the wood stove and closed one valve that force the water from the water tank to flow through the copper loops to get to the outlet valve and bled out all the air. I'm now on the second season with this system. In the summer a solar hot water heater heats the water in the tank in the loft. I did have a thermosyphon system for many years. Last year I switched to a vacuum tube system in a better solar window on the roof. That made it necessary to use a pump and controller. If I don't close one valve the pump on solar heater loop will also pull water through the wood stove and ceiling loop. I could put in a check valve but so far I've controlled it manually. That allows me to sometimes put solar heat into the house instead of only into the water tank.

I also use a ecofan and a slow 12 volt fan to stir the air around the wood stove. We have 3 clothes lines near the stove that the fan helps dry the clothes. But most of the heat is now moved by water, and it is a lot cooler near the stove.

Chris
« Last Edit: November 21, 2007, 10:13:45 PM by hydrosun »

MVIDSMITH

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Re: Heating with wood options
« Reply #12 on: November 22, 2007, 09:52:29 AM »
I now have a book on using a rocket stove mass heater. it store heat in a cob bench and also in a cob bed platform. I have yet to build a model so I cant give you any efficiency but it is an interesting concept.


Mark

« Last Edit: November 22, 2007, 09:52:29 AM by MVIDSMITH »

ghurd

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Re: Heating with wood options
« Reply #13 on: November 22, 2007, 10:15:51 AM »
A old-timer wood/coal furnace guy told me most DIY tries to get the heat to the cold places,

And that's a mistake.

He said it's better to think about getting the COLD air back to be heated. The warm air usually takes care of itself.


Started thinking about one under floor duct with in floor vents, from very near the stove to the other end of the house.  I think it would circulate the cold air back to the stove without a fan.  Not sure.


G-

« Last Edit: November 22, 2007, 10:15:51 AM by ghurd »
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TomW

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Re: Heating with wood options
« Reply #14 on: November 22, 2007, 11:13:21 AM »
G;


As a matter of course I always move cold air into the room with the stove. Just a 20" window fan on "low" on the floor can warm a room quickly by this method.


Since it is basically a closed loop if you push cold air into the warm room it will spill its warm out to the other room.


Our house is pretty small and basically 2 rooms and a hallway sort of thing where the stove sits. Back room is pretty open so it heats easy. Front room is beyond a doorway so heat does not easily go that way. The fan makes it work.


Another little gimmick to destratify the air and mix the hotter ceiling air with cooler lower air is a tube that has a small pc fan in the top and blows upper air down to the floor via the tube. This tube can be anything cloth, pvc plastic sheet, whatever.


Only been heating with wood about 45 years or so so hardly an expert.


Cheers.


TomW

« Last Edit: November 22, 2007, 11:13:21 AM by TomW »

elvin1949

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Re: Heating with wood options
« Reply #15 on: November 22, 2007, 04:17:47 PM »
Tomw

 Like you i ain't no expert [only 58 yr's old]

A friend showed me how dumb i was 10 yr's are so ago.

 He put in a fireplace [0 clearance ]The one's with air intake at the bottom and air output at the top.

You know the one with the heat chamber around the firebox. Well he changed it.

 He mounted it on an outside wall,turned the air intake around so it pulled outside air into the heat chamber. Then he threw the fan as far as he could.

 The normal heat chamber vents into the same room as the fireplace.NOT HIS.He ran ductwork straight up to the attic then to ceiling vents in the back of the house.The draft up the chimney draw fresh air in and heats it and send it to the back of the house.

 The fire feeds on the cold air at floor level.

The damper controls everything [manual or auto.]

All you need is a small bed of coals to keep whole house warm.


 I ain't very good with words so hope ya'll can figure out what i am trying to say.


later

Elvin

« Last Edit: November 22, 2007, 04:17:47 PM by elvin1949 »

SteveCH

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Re: Heating with wood options
« Reply #16 on: November 23, 2007, 02:33:46 PM »
Well, I'm a youngster since I've only been heating with wood for 40 yr. now, but at 8500 ft. in the Rockies. I don't have subfloor heating or anything other than two woodstoves [one a kitchen range which cooks and also heats that half of the house, large stove at the other end takes care of the other half of the building, 1200 sq. ft.]


My best friends live in Wales [between Buckley and Mold, in Flintshire], so I've been around the area. I am wondering, converting an old barn, is it high-ceilinged? If so, the other poster was right about a ceiling fan or fans. You'll have major heat stratification, hot air way up top and cold near the floor, regardless of which system you end up with. You'll save major fuel by cycling that hot air down from the ceiling. There are low-voltage fans available; I just purchase one [about US $200]. They are well worth the money, and even the inverter-powered ones are efficient. Watch out for the old, heavy models, though--they can eat a lot of electricity.


I have a friend with a homemade subfloor heating system, and it works fine. He uses a low-voltage, high-quality circulating pump that sips energy and runs very quietly and has been in operation for about fifteen years so far. He is quite happy with the warm-floor feeling and has had no problems with the system he built for his 1800 sg. ft. home.

« Last Edit: November 23, 2007, 02:33:46 PM by SteveCH »

aguillar

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Re: Heating with wood options
« Reply #17 on: November 26, 2007, 03:57:39 AM »
Some fantastic advice coming in here, many thanks!!!


We have spotted a Grundfos A rated circulation pump that seems to use very little power indeed so this might be a suitable route [then we don't have problems with routing pipes subject to the constraints of a rise along their complete length and can use smaller bore pipes too]. We shall see!

« Last Edit: November 26, 2007, 03:57:39 AM by aguillar »

zeusmorg

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Re: Heating with wood options
« Reply #18 on: November 26, 2007, 06:14:37 AM »
 I personally love heated floors, first off floors are usually the cold spot with any air heating system and there can be "dead spots" that don't get good circulation.

I see no reason you couldn't put an attractive wood burning stove in your main living area, and then use heated floors with a heat exchanger.

Also I'd pick a stove or design that can utilize an outside air source, that way you're not sucking out heat from your living area. Open fireplaces are notorious for that. also using a heated floor solves the air distribution problem between rooms.it sounds like you'll have high ceilings, so ceiling fans or even more effective,free-standing chimneys with fans to pull the hot air off the ceilings.(picture a tube with a fan in it sitting off the floor and ending close to the ceiling, usually in a corner.)

 Just remember with a stove heated water system to include a relief valve,or even two even with an accumulator, a ruptured system isn't any fun!

 Also I prefer some solar panels for those sunny, windless days. It could keep you from starting up your backup generator. Before putting in that wind generator, it would be a good idea to look at your average wind speeds for that area, and buy an anemometer to see what your best location would be.
« Last Edit: November 26, 2007, 06:14:37 AM by zeusmorg »

framistan

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Re: Heating with wood options
« Reply #19 on: November 28, 2007, 06:03:36 AM »
Here is a method of circulating water using a TINY LITTLE

water pump at the top resivoir... the kind of pump you can

buy for ten bucks.  They are used for small water fountains

 (submersible) and they only use 4 watts of electricity!


 


The system is one I am working on to cool a house using

the coolness of the earth.... but you may be able to use

the water pumping method shown.  The advantage of this

method is .... it is not pressurized and if you generate

any steam... it won't explode your pipes.  Also if any

air-bubbles accumulate in your pipes, they will simply

bubble out the resivoir.(pumps dont like air-bubbles).

If the pump wears out, it is EXTREMELY easy to replace.


This pumping method uses the principle of water will

maintain an EQUAL LEVEL in both resivoirs.  The pump does

not have to have any LIFT to speak of.  It only pumps

water from one resivoir to the other.  A "lift" of only

an inch or 2 !!!  so the water will go down the pipe because

the water must maintain an equal level in the resivoirs.

If anyone wants further info on this system, just read

the diaries i have written under the username of FRAMISTAN.


Hope this helps you.

« Last Edit: November 28, 2007, 06:03:36 AM by framistan »

ghurd

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Re: Heating with wood options
« Reply #20 on: November 29, 2007, 04:30:43 PM »
I proposed the same thing for radiant heating.

Put the buckets near the stove, heat exchanger under the floor, no need for a radiator.

G-
« Last Edit: November 29, 2007, 04:30:43 PM by ghurd »
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aguillar

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Re: Heating with wood options
« Reply #21 on: December 03, 2007, 03:42:53 AM »
The wind turbine install is now underway so we hope we have a good site! It is pretty clear where the best spot on our land is for the turbine, there isn't enough space for a huge amount of choice anyway!


Leaning towards a pumped underfloor system, without an accumulator.


The comments coming in are teaching me a lot!! Many thanks everyone!

« Last Edit: December 03, 2007, 03:42:53 AM by aguillar »

ghurd

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Re: Heating with wood options
« Reply #22 on: December 04, 2007, 09:20:02 AM »
Sounds like you need one of CmeBrew's fans, maybe with a little PWM circuit to slow it down on 24V.  It is amazing how much air they move for a drop of power.

G-
« Last Edit: December 04, 2007, 09:20:02 AM by ghurd »
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heatwise

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Re: Heating with wood options
« Reply #23 on: December 09, 2007, 10:16:51 AM »
Go for the thermo-syphon method, option 3. You need to 'throw' the hot water as high as possible. Take a 28mm pipe (FLOW) from the boiler as vertically as possible to the loft floor, fit reducing tee, 22-28-22, (at highest point in this run fit an expansion pipe to run over the header/expansion tank that feeds the heating system). The two 22 mm runs can be taken to opposite ends of the loft and then run vertically down to feed individual radiators, pies can be hidden in the walls (insulate) with 15mm off takes to feed the radiators. The flow pipe work can be reduced to 15mm on the down stairs pipework. Run return pipes from the radiators, initialy in 15mm on the 1st floor and as more radiators are connected and you are working on the ground floor circuit - increase to 22mm. the return connection into the boiler from the last radiator on the circuit can be run in 28mm. Did a this system in a farmhouse I built my-self, 14 radiators fed of a AGA style cooker/boiler - purrrrrfect! All the above in line with good enginering and plumbing practice. Need more info? give me a shout.
« Last Edit: December 09, 2007, 10:16:51 AM by heatwise »

elvin1949

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Re: Heating with wood options
« Reply #24 on: December 10, 2007, 07:35:56 AM »
 If you go to a ceiling fan [I would and do]

remember to run it blowing UP,it will push the warm air down the walls.If you put it blowing down

there will be COLD draft's everywhere.

 With underfloor heating and fans you will

be comfortable.

later

Elvin
« Last Edit: December 10, 2007, 07:35:56 AM by elvin1949 »

scorman

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Re: Heating with wood options
« Reply #25 on: December 10, 2007, 09:09:13 AM »
Instead of a "wood burning stove with back boiler" have you considered an oversized steel masonry firebox with a double wall "heatalator" air circulation system??


I have this one installed in my "great room":

http://www.yourwayfireplaces.com/docs/Air%20Circulating%20Metal%20Fireplaces.pdf

I can burn 24 inch logs easily


since you are talking "offgrid", the entire heatalator system can be driven with (2) 4" 100cfm 115v box fans which draw only 10 watts each and are probably available for puters at 12v (but don't ususally have enough cfm).

If ducting is from basement up to above floors, then convection adds to circulation.

Floor registers are another way to suck hot air off basement ceiling to living space above.


The mass of masonry/chimney adds to the heat capacity of the unit ..my masonry chimneys go up through the center of the house, and the exposed hallway in living space is bricked wall for passive radiation.


In another installation in a parallel thread, I also have installed a plate hot water heat exchanger at the rear of the firebox connected to my baseboard hot water system, as well as a stack heat exchanger connected to the forced hot air ducts:

http://www.fieldlines.com/comments/2007/11/26/184016/10/16#16


I later posted some pics of hardware:

http://s145.photobucket.com/albums/r203/scorman1/fireplace/


If you still like the idea of domestic hot water and/or baseboard, I would recommend wrapping cylindrical coils of 1/2"x50ft aluminum tubing around the outside of the metal flue just above the firebox before enclosing it in masonry:

http://www.plumbersurplus.com/Cat/Aluminum-Utility-Tubing/269/List?attribute_value_string|Brand=D.O.
+Smith

Easy to use compression fittings to connect to copper water lines


IMHO a circulator pump of some sort is a requirement or you'll easily boil the water.

The newer high tech designs are very energy efficient ie only take 60 watts ie Taco 1/40hp


Stew Corman from sunny Endicott


BTW, I would replace the typical installation of "glass firedoors" to effectively make the firebox into a furnace ala the old Franklin cast iron fireplace doors which closed off the entire face of the open fireplace ie check out my pics of steel doors


Stew Corman from sunny Endicott

« Last Edit: December 10, 2007, 09:09:13 AM by scorman »

ghurd

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Re: Heating with wood options
« Reply #26 on: December 11, 2007, 06:27:43 AM »
The old tech pumps aren't bad either.

A March 809 24V feeding 8 parallel 300' runs of 1/2" is drawing 0.52A with 24.7V batteries.  12.8W!

G-
« Last Edit: December 11, 2007, 06:27:43 AM by ghurd »
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sbotsford

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Re: Heating with wood options
« Reply #27 on: January 10, 2008, 10:58:24 PM »
A thermal siphon doesn't have to increasing over the full length.  It will work as long as the radiator is above the heat source.


The idea is that you have a loop of water.  If you heat one side of it, the hot water takes less volume, so that side is lighter, and you get convective circulation.


I think you would be better off to run the initial section of pipe at a steep, but not vertical angle.


Sometimes thermal siphons can stall.  For circulating hot water, the issue can be that pipe diameter is too small to initially fill with hot water to start the siphon.

Run large diameter pipe for the steep section, and put the manifold that splits it into separate lines near the ceiling.  This may allow enough room for convection to fill the riser pipe.  If it's vertical, there is no preference for which side the convection starts on, so it doesn't start.  On a slope, one side is higher, so the convection tends to start upward on that side.


You can demo this using a chunk of small diameter hose or pipe.  Immerse in water, block one end, then raise whole thing up, with the open end held so the opening is facing straight down.  If done with care, the water doesn't pour out while the air pours in.  Now tilt to one side a bit.


Another example:  Fill a pop bottle.  cover opening.  Hold straight up and down, upside down and open.  Time how long it takes to drain.  Repeat with bottle held 30 degrees off vertical.  time how long it takes to drain.  The second one should be faster.

« Last Edit: January 10, 2008, 10:58:24 PM by sbotsford »