Author Topic: Heating a kiln with outdoor wood boiler? (Read 1611 times)

KWood255 · « **on:** April 06, 2022, 08:30:24 AM »

Morning all,

I am exploring options for building a kiln to supplement my business. Our electricity rates are very costly here in Northern Ontario, so I’m trying to avoid more of that. My thoughts so far is to utilize an old reefer trailer, or get a sea can and insulate it. I already heat my home/shop with a central boiler OWB, so I could potentially run a third set of lines to heat the kiln. Has anyone here done this? Any experience to share? Proper ventilation would be my next issue.

I have very limited knowledge on kilns, but I realize heat and dehumidification are two different things. Will heat alone work, if fans and ventilation are incorporated? Thanks for any suggestions.

GeneWengert-WoodDoc · « **Reply #1 on:** April 06, 2022, 09:28:46 PM »

It takes three environmental conditions to dry wood…temperature, humidity and air flow. When you heat air, it’s humidity drops, so we need to be careful it is not too dry. We can close the vents and recirculate the air, but when the heater comes on bringing new air, the humidity will drop. This is why most kiln do not put hot air directly into the kiln, but use a heat exchanger. Air to air exchangers are not very efficient however, so they have to be fairly large.

What species and thicknesses are you thinking about?

xlogger · « **Reply #2 on:** April 07, 2022, 06:23:21 AM »

Quote from: KWood255 on April 06, 2022, 08:30:24 AM

Morning all,

I am exploring options for building a kiln to supplement my business. Our electricity rates are very costly here in Northern Ontario, so I’m trying to avoid more of that. My thoughts so far is to utilize an old reefer trailer, or get a sea can and insulate it. I already heat my home/shop with a central boiler OWB, so I could potentially run a third set of lines to heat the kiln. Has anyone here done this? Any experience to share? Proper ventilation would be my next issue.

I have very limited knowledge on kilns, but I realize heat and dehumidification are two different things. Will heat alone work, if fans and ventilation are incorporated? Thanks for any suggestions.

I have my kiln connected to my central boiler here in NC. Works great call Stan at Nyle if you get one from him. He will help you setup.

jpassardi · « **Reply #3 on:** April 08, 2022, 08:52:47 AM »

Quote from: GeneWengert-WoodDoc on April 06, 2022, 09:28:46 PM

It takes three environmental conditions to dry wood…temperature, humidity and air flow. When you heat air, it’s humidity drops, so we need to be careful it is not too dry. We can close the vents and recirculate the air, but when the heater comes on bringing new air, the humidity will drop. This is why most kiln do not put hot air directly into the kiln, but use a heat exchanger. Air to air exchangers are not very efficient however, so they have to be fairly large.

What species and thicknesses are you thinking about?

I believe he's proposing to use a water to air heat exchanger so it would be heating the moist air in the kiln, not replacing it. Bear in mind that he's using a hydronic boiler.

KWood255 · « **Reply #4 on:** April 09, 2022, 07:38:36 AM »

Yes, this is correct. The outdoor wood boiler will be plumbed to a heat exchanger/fan inside the kiln. Incoming Water temperature would be 160-180*f. I would expect the air temperature could reach 120f+, perhaps higher in the colder climate. Summer time would be easier to increase heat for sterilization.

Moisture removal from the kiln is my greatest concern. I do not know if a couple household dehumidifiers would work…I suspect not well.

I would much rather buy a compete kiln from a known manufacturer, but it is not in the budget right now. As I mentioned above, using the wood boiler is a form of free heat that is difficult to steer away from.

Don P · « **Reply #5 on:** April 09, 2022, 08:48:17 AM »

If the heat is free you don't have to be as fussy when you're done saturating it. Rather than using more equipment and energy to strip the moisture out of it (DH), just vent it, suck in a new charge of outdoor air, heat it up till saturated and dump that. Heat,vent, heat, vent. Your kiln control has it's foot on the heater and vents while watching the temp and humidity in relation to the set points you have told it to maintain for that "step" in the drying cycle.

A friend has his Nyle set up beside the OWB. We haven't hooked them together yet. It will be interesting to play with the pain points. It runs DH now. The chamber could run fully heat/vent, or anything in between with a blend of the two systems. At least here there is no more expensive way to make heat than with the current kiln's electric heater. I guess my point is, there are any number of ways to dry, the goal is to set up and control the drying conditions.

xlogger · « **Reply #6 on:** April 10, 2022, 06:45:44 AM »

If you get the Nyle 53 it will not run heat and dehumidifier at same time but Stan can tell you how to hook up to OWB so you can run both.

Don P · « **Reply #7 on:** April 10, 2022, 08:26:19 AM »

This is a conventional kiln schedule, I just grabbed one out of the tables, they are set up by species groups and thickness. These are usually safe starting points for a conventional steam heated kiln. The heat input and venting maintain those conditions inside, step by step as the wood dries. Watch the depression as drying proceeds. For instance a solar kiln tries to maintain something along the lines of those depressions albeit at a lower curve of temperatures, so for more time.

K-Guy · « **Reply #8 on:** April 11, 2022, 04:20:22 PM »

If you are going to try doing a conventional(not DH or vacuum) kiln with a wood boiler you need a lot of btus, a high flow rate on your pump and a holding tank that can keep up.

ToplineMike · « **Reply #9 on:** September 25, 2022, 02:00:27 PM »

I've got a 63X40 shop that is heated with in-floor heat with my outdoor wood boiler. I would like to section off around a 10'x20' area in the shop to use as a kiln. The existing shop is fully insulated, with a 10' ceiling. I have a new to me sawmill, and plenty of oak and aspen in my woods. I could easily mill up the lumber for the new structure. Any thoughts on this pipe dream I have?! I will talk to Don at Kyle about this also.
Thanks for any input.

doc henderson · « **Reply #10 on:** September 26, 2022, 03:23:08 AM »

rather than use the floor that happens to be under the kiln, it may be better to have a floor with more length of pex in it (meaning closer together) so that more heat comes into the floor. as well it could have a heatsink in the walls, and if you plan to heat above the comfort level in the shop, (and especially in the summer) you will want insulation in the walls of the building within a building, or in a separate building.

doc henderson · « **Reply #11 on:** September 26, 2022, 03:24:39 AM »

Oak needs to go slow and aspen can go fast. you can start these outside air drying, then finish them with some heat. the water that heats the kin should be on its own circuit with its own thermostat.

ToplineMike · « **Reply #12 on:** September 26, 2022, 05:05:33 PM »

Quote from: doc henderson on September 26, 2022, 03:23:08 AM

rather than use the floor that happens to be under the kiln, it may be better to have a floor with more length of pex in it (meaning closer together) so that more heat comes into the floor. as well it could have a heatsink in the walls, and if you plan to heat above the comfort level in the shop, (and especially in the summer) you will want insulation in the walls of the building within a building, or in a separate building.

I plan on running a water to air heat exchanger in the kiln. It should heat up very easily with insulated sawdust walls! I'm not sure sawdust insulation is "legal", but it sure does insulate well.

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