OWB & High Indoor Temps

[bodhisoma]

I've noticed a couple of threads where people have made comments along the lines of being able to enjoy relatively high indoor temps (70-74F) because of their OWB.

Is this because since the OWB is in a constant state of burning, the cost/benefit to the heating system is non-linear as opposed to propane where the cost/benefit is likely quite linear, or substantially more linear? In other words, it costs $x to run at 65F but $x + 1% to run at 75F because the water is being heated anyway.

Or is it because the cost of wood is so much less than propane so owners of OWBs can simply afford to heat that high?

I'm guessing the former but what I don't know about HVAC and thermodynamics is embarrassing.

 

[AIM]

It's because it is non linear as you say. It takes very additional little wood to keep my house at 74 versus 68. My house is small and pretty well insulated though.
Now if you had some huge old farmhouse with bad windows and poorly insulated. It would start to lean towards the wood is cheap side.

Every time your blower fan runs in your house you are drawing more heat off your water. Your wood has to put that heat back. The more it runs=the more wood has to burn.

My shop is poorly insulated and when I heat that, I eat up considerably more wood.

 

[russhd1997]

I cut the wood for my OWB on my own land and take what others give me as well. The actual cash out of pocket to harvest and process the wood is minimal compared to the cost of heating oil. Therefore setting the thermostat at a comfortable level cost very little. Most of the OWB owners that I know enjoy the same luxury. Just one tank of heating oil would cost me far more than what I spend on gas for my chainsaws and other equipment.

 

[AIM]

I'll bring up a couple of points that I have made in the past.

1. Wood is not free. If you sit down and really figure every little penny you'll likely cone up with about $6 - $10 per truckload. (or about 1/2 cord)

That being said brings us to the next point.

2. A poorly insulated house will still be inefficient to heat regardless of your heat source.

I think us OWB guys ignore this fact more than most. If we were to spend a little time and money on insulation, windows, etc. We could drastically reduce our time cutting wood. Which in turn allows us to gain more from our $6-$10 truckloads.

 

[rancher2]

I have pasture land that needs cleared and cleaned up. So burning wood makes sense. But having good insulation and good windows sure helps too. I haven't purchased any propane in 5 years. We still use it to dry clothes and run the hot water heater once an a while. I burn my Garn year around to heat water. We keep our three story farm house at 75 degrees in the winter.

 

[bodhisoma]

Thanks for the replies!

My house is pretty small, ~1,800 sqft, and VERY well insulated.

The reason I ask is despite having 7 acres at my disposal, our budget is tight, I don't yet have the equipment and haven't yet gone through the chainsaw training course so I'm currently bucking felled wood with an axe and dragging it out by hand. Therefore the cost is rather high for me right now with a new baby and all.

So I'm trying to figure out if having temps all the way into shorts-and-t-shirt land consumes significant or marginally more wood. AIM seems to feel the additional load is marginal, and I'm inclined to agree on intuition alone, but I'm not yet sure.

See, my thinking is that with propane/oil, the system turns on and consumes the fuel as needed. It's efficient, the propane is converted to heat at a high percentage and most of the BTUs thrown off get ported throughout the house with nominal waste through the ducting and since the heating element is inside the house, what loss does occur through the venting winds up in the house anyway, what's actually lost is distribution focus.

With wood, it's constantly burning, less of the combustable material is converted to heat energy and heating a box that is losing heat to the surrounding area.

Granted, when the air is blown across the coils, the water contained within is cooled which, in turn, requires energy to heat, which comes from the wood, but I don't see that cool water dropping the temperature of the firebox appreciably more than the other vectors, which is why wood heat is relatively inefficient (~60% for my CL-5036 vs. ~85% for a similarly modern propane heater).

Therefore significantly more wood isn't consumed to reheat that box compared to that coil not being there at all.

Maybe I'm wrong on that, gut feelings on things like thermodynamics, I would imagine, often are.

Interested in seeing more thoughts on it, especially from actual HVAC people if any are around.

 

[AIM]

Not wanting to downplay safety but I wouldn't wait for a chainsaw safety course. Find a neighbor, a guy from a tree service, or just about anybody that has ran a saw for a while and just ask for an hour of his time.
I'm just sayin I would do this before I used an axe.

 

[Oxford]

If that thing is 60% efficient, I'm #### Cheney. The best I've ever heard on one of that design is 30, and I can't find documentation of that. Not an OWB naysayer in general, but they're not efficient in any meaningful sense of the word, especially in comparison to modern gas appliances that run 90%+ reliably.

 

[Storm56]

I have no idea how efficiency is measured in an OWB. But what I can tell you is that I heat my 1900 sq ft home, 900 sq ft attached garage, 4900 sq ft pole building, domestic hot water and hot tub on about 10-12 cord per year. I live in NE PA. IMHO that is pretty efficient. I have my own wood on the property and do not have to buy any. No doubt if I tried all this with fossil fuels or electric I would have a bill that far exceeds the cost of wood even if I bought it at the local going rate of about $200 per cord.

 

[Encore]

Thanks for the replies!

My house is pretty small, ~1,800 sqft, and VERY well insulated.

The reason I ask is despite having 7 acres at my disposal, our budget is tight, I don't yet have the equipment and haven't yet gone through the chainsaw training course so I'm currently bucking felled wood with an axe and dragging it out by hand. Therefore the cost is rather high for me right now with a new baby and all.

So I'm trying to figure out if having temps all the way into shorts-and-t-shirt land consumes significant or marginally more wood. AIM seems to feel the additional load is marginal, and I'm inclined to agree on intuition alone, but I'm not yet sure.

See, my thinking is that with propane/oil, the system turns on and consumes the fuel as needed. It's efficient, the propane is converted to heat at a high percentage and most of the BTUs thrown off get ported throughout the house with nominal waste through the ducting and since the heating element is inside the house, what loss does occur through the venting winds up in the house anyway, what's actually lost is distribution focus.

With wood, it's constantly burning, less of the combustable material is converted to heat energy and heating a box that is losing heat to the surrounding area.

Granted, when the air is blown across the coils, the water contained within is cooled which, in turn, requires energy to heat, which comes from the wood, but I don't see that cool water dropping the temperature of the firebox appreciably more than the other vectors, which is why wood heat is relatively inefficient (~60% for my CL-5036 vs. ~85% for a similarly modern propane heater).

Therefore significantly more wood isn't consumed to reheat that box compared to that coil not being there at all.

Maybe I'm wrong on that, gut feelings on things like thermodynamics, I would imagine, often are.

Interested in seeing more thoughts on it, especially from actual HVAC people if any are around.

Best way to measure that is to try it for a few days and see what happens. Like others have said, the difference between 69 and 73 in my house is pretty slim. But if I'm gone and run the house at 67, it does use less wood. The other thing we have to consider is the hot water usage though. The burner will definitely eat up more wood when there is a large draw on the hot water (showers, laundry, dishwasher) but because everyones setup is different you may have different results.

Also, I agree with others there is no real reason to take a chainsaw course if you have common sense and someone with good experience to teach you.

 

[rob206]

Wow. Am I reading this right, you currently have a OWB and you are chopping wood with an axe? Man, you have some brass. Get a name brand(not from a box store) saw asap, read the manual thoroughly and commence to cutting. Oh, and don't forget PPE.

As far as your original question, just see for yourself. Turn up the t-stat and take notes. I don't keep our house that warm, ie above 70, so I can't offer any accurate input.

 

[jh35]

My wife likes the house at 74 deg F. Therefore it is.

No really. I don't mind the little extra wood that it takes. I don't buy wood but I do have the expense of cutting and hauling, although much less splitting now that I have my OWB.

Way back when we were first married before any wood furance we kept the house under 70 to keep the costs down. I hate paying for propane.

 

[VTWoodchuck]

My house is very tight, was built in 2007 and we have large western facing windows. I find that setting the temp at 72 or so doesn't make that much difference in wood use then say 68. I cut all my own wood as well.

To the OP- Get a saw ASAP! Buy chaps and steel toes boots. Read your user maual for the saw. Watch some vidoes, Stihl and Husqvarna have them. Some good shops will give you a good run down of the basics, find one local to you.
Also I've seen some guys on here post vids of felling and bucking(bsnelling and mweba come to mind).
Even if you just get logs delivered and you buck em up, you're saving money. You can ask for no logs over 16" or so then you have minimal splitting to do.

 

[howellhandmade]

There are lots of bad things that can happen when you use any tool, but no course can save you from all of them.

Personally, I wouldn't buck logs with an axe unless I was training for timbersports competition, and I know a few people who have had some foot problems using an axe. I'm not sure it's all that much safer in the long run than using a chainsaw for bucking. Unless you have something under tension, bucking is one of the safer things you can do with a chainsaw. If I had to I'd use a crosscut saw or a big bow saw.

If you read the owner's manual, apply common sense and understand how forces are stored in a log and where they go when released, you will be as safe as anyone can be with a chain saw. I started on my own with a chain saw without any teachers, not even the internet. I've watched safety videos on YouTube since then, and they mostly consist of information that is in every owner's manual, and things that only need to be said because people don't think about the physical world anymore. They don't think about what materials weigh, or where they will go if they fall. They need to be told where to cut a fallen branch so that it doesn't bind the chain, or so that the rest of it doesn't spring back and clobber the operator. They need to be shown what kickback is and how it happens.

I understand the feeling of wanting supervision learning to use a tool and I don't mean to disparage that. I do think, though, that if you can buck logs with an axe you can buck them with a chain saw. I wouldn't start felling right away.

Good luck.

 

[bowtechmadman]

I keep the house at 73 and dhw ion occasion 30*40 barn. Fortunate that I don't have to buy wood so never tried to run lower temps to study wood usage. We do drop temps to 60 when we will be away for a long weekend and have. Held a fire for nearly 72 hours before. I think id try a bowsaw or crosscut saw over an axe to buck. Who am I kidding...id buy fuel oil if it wasn't for chainsaws.

 

[alvise]

I have to heat 3 house with 2 OWB.
You have to look behind the economics to make your choice on how you want to heat.
- Do you enjoy going outside cutting wood ?
- Do you have access to wood?
- Do you have the equipment to cut, buck, move , split ?
- Do you have a space where to store and season the wood ?
- Do you have the time to do it ?
Some time I loose the real economics on the heating business, i have 60 acres of forest, quad, tractors, trailer , 4 chainsaw, 40Hp 3PH wood chipper, 20t gas wood splitter and 30k $ in OWB.
With all the machinery already paid and considering only running cost (gas etc) if I pay myself 20$/h I'm probably better to have a gas furnace and go somewhere else working and with the income pay the gas bill.
If you like to spend time in the forest sweating and you have enough time is another thing.
If you are making your decision now think well and think twice if is really what you want, once you start is hard change direction (too much money invested)
If you have a well insulated house with a compatible design (open) a way to go could be a masonry stove (tempcast or similar) inside the house (super efficient and clean) that can heat the all house and a small backup gas system that you use also for your domestic hot water. The stove is bulletproof and nothing can go wrong (pump, corrosion, blowers etc) .
PS if you have time a truck and a skillsaw you can harvest a lot of "free" firewood from pallet that people normally give away.