Outdoor Wood Boiler With Short Run on a Heat Exchange

sniz

I'm shopping for an OWB and only need it to run about 75 feet to our utility room where it will connect to a heat exchanger. I'm assuming I wouldn't need a very big OWB but I would still want a very efficient one. I'm new to this OWB world and have some questions.

1. How often would I need to fill it?

2. Can you stop a OWB for a week and start it again the next week? Our weather fluctuates and I would imagine we wouldn't need to heat the water if we have an electrical backup that would be enough while the weather is up.

3. What OWB would you recommend?

Thanks in advance!

Hot_water_fan

This is a great resource:

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

Jamie Hall

First, before you go any farther, check your local codes. Not all jurisdictions permit outdoor wood boilers, and some have restrictions on them. Best to get that sorted first.

The size boiler you need is determined by the heat loss which you are trying to power. Distance has nothing to do with it.

How often would you need to fill it? Most likely at least every day, and in most cases twice a day. It depends, of course, on how hard it is firing and how big it really is.

Can you start and stop a wood boiler? Sure. Just let the fire go out. It can't be done quickly -- it may take hours to cool down -- but it's not hard.

leonz

sniz said:

I'm shopping for an OWB and only need it to run about 75 feet to our utility room where it will connect to a heat exchanger. I'm assuming I wouldn't need a very big OWB but I would still want a very efficient one. I'm new to this OWB world and have some questions.


1. How often would I need to fill it?

You will have to fill it often especially during freezing and near zero temperatures as the boiler will cycle on and off wasting wood fuel when the high limit temperature is satisfied.

This goes along with "how often will I have to empty the ash pit"=every day

If you have scorched air heat or hot water heat your will need to fill it several times per day because these things have poorly designed combustion systems and built with a great deal of pie in the sky, head in the clouds promises from the manufacturers of these things.

To have the most efficient wood boiler you need to batch burn the very dry firewood to heat a great deal of water in an intense fire to burn all the smoke in multiple fire tubes in a hot water heat exchanger.

When the high limit aquastat is satisfied the solenoid controlled damper door for the forced draft fan slams shut and the fire idles and generates a great deal of smoke than can and will be considered a nuisance by your neighbors and they could file a complaint with the municipality you live in and they could force you to stop burning wood- it does happen, and it did happen in the City of Geneva, New York.



As you are going to be heating water or a water antifreeze mix a lot is going to depend on the following:

a. whether you buy an open or closed system
b. what your low limit and high limit temperature is going to be as it affects the evaporation rate in an
open system
c. how much area do you have to heat and what type of hot water radiation you have.
c1. You will need the very expensive closed cell foam pex pipe to deliver the hot water to your home and return the cooler water to the forest eater and it will cost $15.00+ tax per foot. you will need to have a 4 plus inch hole drilled in the wall of the room where the pipe enters the home.
c2. you will need a backhoe for a whole day to dig the trench long before you set the boiler on the concrete pad as you have to have the pex pipe and the electrical conduit in the ground and exposed to connect it to the forest eaters plumbing. The concrete pad has to be reinforced and large enough and thick enough to support the weight of the boiler and the water volume in it.
c3. Your system will have to be inspected by an electrical inspector and plumbing inspector before the trench is back filled filled.
d. what type of wood you have to burn and whether it is soft wood, hard wood or lumber mill discards
e. how dry the wood is when you burn it and whether you have a place to store dry wood
e1. finely split wood burns best and gives the most heat using small intense fires
e2. a fire brick lined firebox provides the best case scenario for clean burning and maximum heat
generation as long as the firebox can shed heat into a large water mass before it travels out the flue
breech and into the chimney
e3. How close is your nearest neighbor and does anyone in your family or the surrounding area have
asthma or could possibly develop asthma?
f. are you willing to get fully dressed and go out in the middle of the night and fill the forest
eater/smoke dragon to keep the fire going at 3AM in the pouring rain or a during snowstorm and
shovel snow off the wood pile to get to it?
g. are you willing to go into long term debt for a 10K-15K installation cost before you even put a fire
starter in the firebox
h. can your spouse, rug rats, dog or cat go out and fill it if you are incapacitated?


2. Can you stop a OWB for a week and start it again the next week? Our weather fluctuates and I would imagine we wouldn't need to heat the water if we have an electrical backup that would be enough while the weather is up.

Yes, you can do that but solid fuel systems usually have a dump zone for excess heat.

3. What OWB would you recommend?

www.garn.com







Thanks in advance!

leonz

Hello Sniz,
You may as well look at pellet boilers if you want to heat your home
with wood and also heat your domestic hot water.

hot_rod

What is you reason for wanting an OWF? They can be a lot of work, and may only make $$ sense if you have access to free, good quality wood

GroundUp

First off, what are you trying to heat and where? The EPA crashed down pretty hard on the OWB industry back in 2015 and while anything goes in Canada, US states are VERY limited on what's legal to install. For maximum efficiency, you want to fire twice a day and only load as much wood as it takes to make it to the next firing- NOT fill it full and see how long it goes. Yes, you can shut it down for a week if temps allow but keep in mind that cold starting these things creates a lot of condensation in the firebox especially if your wood is over 15% MC, which in turn mixes with the wood ash and creates a caustic paste. This can make for very rapid corrosion and premature failure of the firebox. Cold starts should be kept to a minumum. If you're on Facebook, there are some great OWB groups on there with a wealth of information on this subject.