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outdoor wood furnace with gas on demand hot water  RSS feed

 
mike clark
Posts: 43
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has anyone tried outdoor wood furnace with on demand gas hot water.i am told your house and hot water can be heated from fall to spring and when stoves out the on demand gives you hot water in summer.
 
allen lumley
pollinator
Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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mike clark : For many people the on demand option is a great way to go, especially if you can place the kitchen with its hot water needs, and the bathroom
with its separate hot water needs back to back,sharing a common wall, and minimizing the hot and cold water runs. For many people the convenience of
near-instant hot water is a great boon that they soon find that they are unwilling to live without !

The largest caveat to this for most people is a requirement to have a water softener plumbed into the hot water system so that all of the water to be heated,
is 1st run through a water softener, failure to use soft/softened water will result in mineral/metal deposits within already small tubing of the on-demand water
heater.

Please understand that while I have had some practical experience with field chemistry, I do not hold myself as any kind of an expert in this area, but -
It is one of those unexpected quirks of chemistry specifically pH and ions, that A strong acid will barely degrade copper and will destroy iron, but a strong Acid
solution 'Working' on dissolving the minerals and metal deposits will quickly lose pH and at a point close to the level of vinegar start to corrode copper -

I have some memory of seeing a You-Tube video that showed how to take an on-demand hot water heater apart, to replace an (unspecified) damaged heat
exchanger ! It was not a job for an amateur and I would plan on taking scads of pictures in every part of the process, and I have a 20 + years experience
working with Domestic hot water !

O.K. Now that we have the easy one out of the way, lets tackle the outdoor wood furnace/boiler. In order to earn an E.P.A. sticker warranting the efficiency,
and air quality, the Best of the outdoor, wood fired boilers need to show that they can produce a stream of hot water, while producing a a minimum exhaust gas
(smoke) Temperature of at least 500F, this is still a lot of heat going to heat all of the out doors, but lower temperatures will always work to create Creosote !!!

I said that the manufacturer must meet these minimum standards when the unit gets tested by the E.P.A., Once the unit gets installed at the home owners place
it is up to the home owner to continue to operate their wood fired boiler in exactly that manner, The large wood fired boiler can not work like an on-demand
water heater, so the home owner builds a fire in the boiler, runs it wide open for a little while then chokes the fire down to 'have some burning wood embers'
for later in the day, if the owner remembers when he comes home he can reload the wood boiler with more wood and heat up some more water, however
during the several hours of untended operation while the fire has been 'choked down' the boiler is no longer operating in the manner as specified by the
manufacturer or tested by the E.P.A. Operated in this manner the boiler makes more Creosote than hot water !

There are models out there that can not be run this way, they have automatic air dampers that will open to provide additional air to the boiler when the stored water
temperature falls, these models will then quickly burn through the wood in the boiler, then the boiler cools down because you have a constantly open damper that
lets the stored heat of the boiler itself and the heat of the boilers water pass up the exhaust gas chimney, the average wood fire boiler owner who finds that they
have no hot water will complain to the company that sold and installed the boiler, and will be advised to unhook the automatic damper before they go away for the
day!

I can set right here in my chair and write a thick book about all the ways that the owners of a Wood fuel fired Boiler can sabotage themselves, one of the easiest is to
open a hot water faucet and get steam and spitting water, they run outside to the boiler, look at the water level gauge for the amount of water in the boiler, and
remember that they had not thought about checking it for several days, and open up the water feed valve dumping very cold water into a hot boiler, this act will shock
the boiler cracking the cast steel walls and ruining the entire boiler !

If you think that you are interested in a wood fired boiler, plan on going out and inspecting several installations 1st, It is very common in January to see green grass
growing directly over the water supply lines going from the boiler to the house even while there is several inches of snow outlining the path from the boiler to the house !

Think like fire, flo like gas, don't be the Marshmallow, As always, comments and questions are solicited and Welcome ! PYRO - Logically Big AL
 
R Scott
Posts: 3351
Location: Kansas Zone 6a
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I have an indoor wood water heater (Amish cookstove with water front) that supplies all my winter hot water. I looked at the options for summer hot water and found I could:

1. Use solar hot water. It was almost a match, but a few times in the rainy season or shoulder season I would need a third option as it was too cool for solar and too warm to use wood. Not an issue with an outdoor boiler.
2. Gas on-demand unit. You need to find one for a solar system, as most expect cold intake water and will steam flash (boom squish) if you pump warm water into them. You also need a serious gas supply, I would have needed a separate propane tank dedicated to it.
3. Standard water heater (gas or electric) as your holding tank. It may take an external heat exchanger and $50 in plumbing parts to hook up to solar or boiler--but still cheaper than a dedicated solar tank. The tank kicks in when needed.
4. Use a heat pump water heater (google nyle geyser). This runs like an air conditioner in the room, but pumps the heat into your water instead of outside.
It doesn't recover as fast as a regular water heater so you need a bigger holding tank, but it provides cooling and dehumidification while in use (two things you usually want in the summer).
It is under 2,000 watts when running, so it is in the range that a moderate solar system could run it.

I found the on-demand units really expensive for the way my family uses water. For a single or couple that don't use hot water often, they can make sense. I went with (3) and moved to (4). The heat pump was about the same price as an on-demand big enough for my family, but since I could stack dehumidifier and AC use it is essentially free to run.
 
M Foti
Posts: 171
Location: western n.c.
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I know this is an old post, but wanted to share some info for folks who may find this in their searching... having a stove/furnace/boiler plumbed like this can be a bad idea... Aside from the furnace running away and causing steam (bad), you have the problem of what if your fire goes out? Then the water will freeze and you'll have some serious repairs to do. Outdoor boilers have a sealed, separate "water" system, this is treated with a "less dangerous" anti-freeze like you would use in an RV for winter storage. That heated fluid is then run to a heat exchanger to heat your hot water with, much the same as a professional solar water heater is. I have seen some of my friends loop copper pipe around their flue on an indoor wood heater, it kinda worked, but wasn't great, had a few seconds of super hot scald your hands water, then a few minutes of luke warm, then room temperature if they were lucky.

In a wood fired boiler, you have a storage tank to store the hot water and it is circulated through the heater, by just running your house water through the boiler, you have no circulation when the water isn't running out of a faucet.

You then have special pumps to handle the heated liquid, insulated piping so you don't lose your heat, insulated storage tank, and a heat exchanger of some sort. All of this can be home built, but it's not easy to do. A heat exchanger can simply be a copper coil of your heated fluid snaked through an old hot water heater tank, BUT... you have to be able to get the copper coil in there and make bulkheads that will hold the pressure that your house water is running at. Quite a few hot water heater tanks are glass... If you can weld stainless steel and weld it to hold pressure, then it's a go. Making it out of other inferior steel will work, but it will rust and who knows how long it will last.

There are other ways to make this, obviously. But, by simply running a line from your house around a wood stove, it's not going to be satisfactory and could prove dangerous. Steam can be very explosive.

I currently build outdoor forced air wood furnaces, they work great in the southern appalachian mountains, not sure how well they would do in an area where it gets REALLY cold though, that is where the efficiency of heating a fluid rather than air would pay off (I heat the air from inside the home, not outside cold air). For myself and all my friends who I have helped build them, they work fabulously, just no way to easily heat water with them. You really have to have an anti-freeze fluid, with a large tank to prevent steam flash, several safety measures just in case steam flash happens, and a heat exchanger not to mention for some reason that I am too ignorant to understand, these water systems coupled with wood tend to fail quickly and have to be refurbished/replaced within 5-10 years.

I have built 1 outdoor wood boiler, ended up costing quite a bit. Be wary of the "price" you're quoted in buying these as they are rarely a price for a turn-key heating system, they usually only include the furnace and storage tanks and not the rest of the system to actually heat your home or water.

Just to add... I found a really nice on demand propane water heater at a local thrift store. Someone donated it, very nice unit, got it for 10 bucks. I've been playing with it, but haven't plumbed it into my system yet, since these things operate on temperature rise and mine has adjustable heating, I'm just planning on running it AFTER my electric hot water heater. I can keep the electric set as low as it will go (somewhere around 90), and then not have to run the on demand water heater at full capacity since it won't be heating 50 degree water. This isn't so much for cost saving as it is for being able to have enough hot water to fill our entire garden tub in one go and to be able to have full functionality of our home using just a small generator if the power goes out for short term storms/outages. In this scenario, I would turn off the electric hot water heater, and use only the propane on demand unit. The only high draw device would be the well pump, whereas a well pump AND an electric hot water heater require a substantial amount of power, this would put you in a large expensive generator category. This may prove to be cheaper on our utility bills since we are a couple and don't use hot water constantly, just to wash dishes and 2 people bathing, for a family it may or may not be cheaper, probably not when you factor in the cost if one was bought new and all the installation material costs.

If someone else comes along and knows of a way that works and works well to heat your water using wood, I would truly love to hear about it. Send me a mooseage as I might not see a post on here! I'm always willing to learn and share knowledge.




 
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