Electrical costs of running a wood boiler

[Eric Miller]

In considering a gassification boiler, one of the benefits I would look for is the production of DHW during the summer months. My proposed system would use a Taco 0010 as the primary circulatory pump. Looking on the manufacturer's web site, I see the pump is rated 1.1 amps at 115 volts, which is 126.5 watts. As it has been described to me, this pump would run continuously; a 126.5 watt pump running 24x7 adds up to 91 kwh a month. That seems like a lot of power to me considering that I've measured my existing electric hot water heater using 300 - 350 kwh per month.

Does anyone have any practical power usage measurements of the Taco pumps? Is the 126.5 watts correct for the 0010?

Thanks.

 

[Nofossil]

In considering a gassification boiler, one of the benefits I would look for is the production of DHW during the summer months. My proposed system would use a Taco 0010 as the primary circulatory pump. Looking on the manufacturer's web site, I see the pump is rated 1.1 amps at 115 volts, which is 126.5 watts. As it has been described to me, this pump would run continuously; a 126.5 watt pump running 24x7 adds up to 91 kwh a month. That seems like a lot of power to me considering that I've measured my existing electric hot water heater using 300 - 350 kwh per month.

Does anyone have any practical power usage measurements of the Taco pumps? Is the 126.5 watts correct for the 0010?

Thanks.

I don't know what configuration you're looking at, but I doubt that there's any reason to run the pump (or keep a fire going) 24/7. If you want to heat DHW with wood during the summer, I'd suggest a really large and really well insulated heat storage tank. Typical family of four uses around 60,000 BTU per day in DHW. A really small boiler generates that in an hour or less. A minimal fire is somewhere around five hours - close to a week's worth of hot water. I do something similar, except that my heat in the summer comes from solar. I have a writeup on my site - link in my signature below.

Try the 'voyeur' link - my daughter is taking a shower, so the pump will likely come on soon to heat the DHW tank from the storage tank.

No, that link only shows heating system data - get your mind out of the gutter ;-)

 

[Bob Rohr]

Why a 0010? Is this the pump required by the manufacturer? Generally wood boilers have very low pressure drop. An 80 watt circ like the Grundfos Super Brute or Taco 007, is generally enough circulator.

Shortly there will be some circs on the market that may be able to move that load with a 40 w consumption.

hr

 

[Eric Miller]

Nofossil,

Thanks, I've been to your web site a few times and have learned quite a bit.

My boiler and an 800 gallon STSS storage tank would be located in a shed about 50 feet from the house. I certainly don't expect to run the fire continuously in warmer months just for DHW, I'm hoping it might be several days between firing. But as the system has been described to me, the circulatory pump would run all the time. That makes sense as it would maintain the temperature in my DHW heater located in the house.

I have X dollars to invest in a new system. Option 1 for me is a gassification boiler. Option 2 is a new chimney, 2nd wood stove and a solar hot water heater. The costs to implement either option is comparable. I only get to spend the money once and I hate to go one way and wish I had done the other.

I don't have any practical experience with either a boiler or solar system so I'm trying to grasp and understand all the nuances of how these systems operate. I was a little shocked to see the boiler would consume a minimum of 90 kwh a month (not counting the draft fan and other boiler power requirement) just for DHW.

Can I use a controller on the DHW tank to enable the circulatory pump on demand? Does water need to be circulated through the boiler continuously to avoid condensation and rusting or does that not apply when the boiler would be off for 4-5 days at a time?

 

[Eric Miller]

Why a 0010?

The 0010 was included in a system quote I received. In addition, to the 0010 there would be three 007s feeding three different zones; 1 forced air exchanger in the basement, 1 forced air exchanger in the attic, and one radiant loop. There would also be another 007 next to the boiler on the return loop to maintain high water temps through the boiler. I've attached the schematic.

 

[Nofossil]

Nofossil,

Thanks, I've been to your web site a few times and have learned quite a bit.

My boiler and an 800 gallon STSS storage tank would be located in a shed about 50 feet from the house. I certainly don't expect to run the fire continuously in warmer months just for DHW, I'm hoping it might be several days between firing. But as the system has been described to me, the circulatory pump would run all the time. That makes sense as it would maintain the temperature in my DHW heater located in the house.

Any chance you could put the STSS tank in the house? It would be better and more efficient.

I have X dollars to invest in a new system. Option 1 for me is a gassification boiler. Option 2 is a new chimney, 2nd wood stove and a solar hot water heater. The costs to implement either option is comparable. I only get to spend the money once and I hate to go one way and wish I had done the other.

I'd suggest that you start with a gasification boiler, and plan to add storage and solar over time. If you're lucky, there may be lower cost solar approaches. I have only a couple hundred bucks in mine.

I don't have any practical experience with either a boiler or solar system so I'm trying to grasp and understand all the nuances of how these systems operate. I was a little shocked to see the boiler would consume a minimum of 90 kwh a month (not counting the draft fan and other boiler power requirement) just for DHW.

Can I use a controller on the DHW tank to enable the circulatory pump on demand?

Yes, absolutely. That's exactly what I do. That's also why you'd like to have the storage near the DHW tank. Every time there's demand, you're moving a slug of cold water from the connecting plumbing.

Does water need to be circulated through the boiler continuously to avoid condensation and rusting or does that not apply when the boiler would be off for 4-5 days at a time?

The condensation concern is when combustion is happening. Flue gases are corrosive if they condense. Your boiler can be cold if it's not burning. However, if it's in a humid location with temperature swings there's probably some benefit to keeping it slightly warmer than the dew point. Folks have suggested a light bulb inside.

 

[heaterman]

Like MOS said. 0010????

System design is everything when it comes to long term operating costs and efficiency. Size your piping and emitters right and you can use a Taco 00R on medium to circulate 150,000 btu's. You'd be looking at about half the wattage of the 0010. It adds up over the course of 10 years time.

On another note.........If the near boiler piping is actually done as shown I think you're going to have a circulation problem through the HX loop in the storage tank. I don't know what may actually be planned but the 0010 as shown will be pulling from the boiler and the tank HX simultaneously. You would also want to locate the bypass circ in the vertical pipe to avoid sending all the system flow through it when it's not running.

Size it right and give some consideration to zone valves and a variable speed circ like a Wilo Stratos. Nearly all systems that I see, wood fired or not, are seriously over pumped.

 

[Nofossil]

Part of the problem is that the DHW is heated via a sidearm only. A sidearm typically has relatively low heat transfer rate, and depends on frequent (if not continuous) circulation. If it's a new system design, consider an indirect tank that has an internal HX coil and acts as another zone. Alternately, consider a bronze circ and an extra HX coil in the STSS, and circulate water from the DHW through that coil to heat it. There are a few other schemes, but it should be possible to heat DHW with only a few minutes per day of circulator activity.

Again, all of this works better if the STSS is near the DHW tank.

 

[heaterman]

Part of the problem is that the DHW is heated via a sidearm only. A sidearm typically has relatively low heat transfer rate, and depends on frequent (if not continuous) circulation. If it's a new system design, consider an indirect tank that has an internal HX coil and acts as another zone. Alternately, consider a bronze circ and an extra HX coil in the STSS, and circulate water from the DHW through that coil to heat it. There are a few other schemes, but it should be possible to heat DHW with only a few minutes per day of circulator activity.

Again, all of this works better if the STSS is near the DHW tank.

The indirect tank is the approach I recommend for nearly all applications. If used in conjunction with the existing water heater it can be utilized as a preheat tank. All the incoming water is already up to temp so the HWH only runs to keep itself warm. Even this can be eliminated with the addition of a very small timer driven recirc pump. This will usually double your stored hot water capacity. One can also pipe in a bypass to take the existing HWH totally out of the picture unless needed for backup or times of extremely heavy use. (House full of smelly in-laws) I'm not a big fan of cheaply made side arms. My experience has been that their performance is directly correlated to their cost. Low. We installed a 30 gallon indirect in front of an existing 40 gallon gas this past winter for a family of 9. The matron of the household says they don't run out of hot water even when both showers and the laundry are running. She has two washing machines to boot.

 

[deerefanatic]

That's what I think I'll do....... Second tempering tank, with a small recirc between it and the main tank... Or just insulate them both really well... At that point, the heat loss from the HWH will be so low that the propane used to keep it hot will be negligible, if not un-measurable......