In the rural areas of Augusta County, out in the beautiful countryside, you don't have to drive far to find an OWB (Outdoor Wood-fired Boiler). If you don't see one, then perhaps your nose will lead you in the right direction. Or just look for a hovering cloud of smoke . . .  

What is it that prompts people to purchase and install these boilers? What makes them popular? Frankly, I'm not sure. Here are some possibilities:

1) Woodlot owners want to use a cheap and readily accessible form of energy.

2) Energy security. Independence.

3) High temperature supply (some people call this "warm heat").

4) Limited involvement. The firebox is large enough that owners only have to load wood once or twice a day.

Let's step back for a moment now, and really analyze the sensibility of purchasing or using an OWB.

HOW THEY WORK

An OWB has the following features: a large combustion chamber, a water manifold / tank, an electric fan or damper, and a short smoke stack. The OWB is coupled to the house through a number of water distribution pipes. A small water pump transfers the heated water from the OWB to the house. Inside the house, the water distribution pipes may be coupled with a hot water heater, a hydronic radiant heating system, or a heat exchange coil inside of an air handling unit.

EFFICIENCY RATINGS

According to one of just a few independent studies, the typical OWB is between 30% - 40% efficient---just half that of an indoor wood stove.

Even more disconcerting, these tests do not evaluate the amount of electricity that is consumed by the OWB. These units require electric power to operate the outdoor fan unit, the hot water pump, and oftentimes, the blower on a forced air heating system.

Although the electricity required to run the outdoor fan and water pump is small, a blower can consume a large amount of electricity. So when we add the parasitic losses of the fan, the water pump, and the blower to the calculation, the efficiency of these units becomes even more dismal.

COST

The current building code disallows wood burning appliances as primary heating systems. So the cost of an OWB is in addition to a more modern appliance---say a heat pump or propane furnace.

The cost to purchase/install an OWB and the associated plumbing can range between $8,000 - $12,000 (an Augusta County resident recently told me they had received a quote of $10,000 to replace their existing OWB). Again, let me restate: this is in addition to the cost of a building's primary heating system!

If we compare the cost of an OWB to an indoor wood stove, it is 2X - 3X more costly, even if we include the expense of a new Class A stainless steel chimney for the indoor unit.

POLLUTION

According to a study commissioned by the state of New York, OWBs produce between 4X - 12X as much particulate matter (smoke) as indoor wood stoves. When compared to a modern gas furnace, OWBs produce 1,800X more particulate matter. No wonder many localities have banned OWBs.

To make matters worse, the smoke emitted by an OWB is near the ground level (due to the short stack height of the chimney). That means the smoke from an OWB is more likely to end up in your house, in your lungs, or wafting across your neighbor's property.

CONCLUSION

So, let's review: an OWB will cost TWICE as much as an indoor woodstove, operate at HALF of the efficiency, and produce 4X - 12X more particulate matter.

If this evidence weren't damning enough, consider this: an indoor wood stove operates passively (stack effect carries the combustion gases up through the chimney). OWBs need electricity. Which one would you rather have during a winter storm induced power outage?

Armory Lovins, a physicist and the founder of the Rocky Mountain Institute, was the first to really define the cheapest watt. He coined the word negawatt---which is kind of the opposite of a megawatt. Actually, it is the exact same amount of energy as a megawatt, it is just that a negawatt is theoretical. It represents energy that has NOT been consumed, or energy that has been saved.

The negawatt is what energy efficiency and conservation is all about.
 
The idea becomes very important when we start to talk about energy production. To illustrate the idea, I’ll use photovoltaic power as an example. Let’s say that you are interested in PV panels, and you are thinking about installing a PV array at your home or business. The first step is to evaluate the cost of saving energy VERSUS the cost of producing that same amount of energy.
 
Let’s use your entertainment center as an example. You have a TV (Energy
Star® rated), a DVD player, audio amplifier, and maybe even an old VHS player.
Each and every one of these devices is drawing power, even when they are turned OFF (they are designed like that for a variety of reasons). In geek speak, this is known as a phantom load.
 
Using a watt meter, we find that together, these devices are drawing (18) continuous watts. It is energy that is being consumed, but not really put to any good use. How much energy does the entertainment center consume per day? 
                 
     18 watts x 24 hours / day = 432 watt hours / day

This system uses 432 watt hours / day. Over the course of a full year, it will consume almost 158 kilowatt hours. At the going rate of electricity, that will only cost about $16 per year. No big deal, right?

To produce an equivalent amount of power with a PV system, we would need to figure out the solar insolation value for the area. The solar insolation value is how much sunlight hits an unshaded part of the earth on the average day---at maximum power. We call this “peak sun hours.” We can find the value here, on the NREL (National Renewable Energy Laboratory) website. For our area, it is approximately 5 peak sun hours / day. Here’s the math for figuring this out: 
                 
     432 watt hours per day / 5 hours per day of sunshine = 86.4 watts
 
Of course, no system is 100% efficient. Most PV systems are “derated” by 15% -20%. Let’s avoid getting too detailed here. We’ll just call it a 100 watts.
 
PV systems are currently being installed for $3 - $5 / watt. That means we’ll need to spend $300 - $500 in order to generate the same amount of electricity that is being consumed by the entertainment center.

That energy is not so cheap anymore . . .
 
What is the cost of saving that same amount of energy? Well, if the entertainment center is plugged into a switched outlet, it wouldn’t cost anything; you would simply have to turn OFF the system at the wall switch, just like you turn OFF a light.

If it’s not on a switched outlet, you could install a power strip and turn it OFF there. Power strips are pretty cheap, usually < $10 each. Most people would find that too cumbersome; they would probably want to install a “smart” power strip like this one. It automatically turns OFF these devices when you power down the TV, eliminating most of that phantom load. These sell for ~ $30.
 
So . . . you can see that the negawatt is the cheapest solution. In this example, it ranges in cost from $0 - $30, compared to $16 for the annual cost of electricity, or the $300 - $500 cost of producing the same amount of energy using a renewable energy (PV) system.

How many negawatts have you produced lately?!