Taking the plunge...

[ken999]

Got the word from the bank today, we will be getting the money for a Greenwood Aspen 175. We plan to set it up temporarily about 30 feet from the house for the remainder of this winter.

Any thoughts or tips would be greatly appreciated. We will be plumbing the new stove into our existing baseboard heat sytem. Our house is 26 by 34 and we have 1 zone in the basement hooked to a Modine heater. I'd like to keep the floors a bit warmer, but don't need to heat the basement as much as the other two floors.

Originally I was thinking of using programmable thermostats to heat the house up a 5 am and again around 3 pm. From reading the threads here about the Greenwood stoves, it sounds like I will be looking at a 8 hour or so max burn time and I wonder if the 'stats will be worth it.

I'm also noticing that some of you are using water storage to help with the heating efficiency. Could someone please explain the theory and necessary items to build such a system? How much do these storage systems help?

 

[LeonMSPT]

Check with a heating engineer on the size of the piping you should use in your loop... make sure the pipe is big enough to remove the heat from the boiler to the house. If it's not, the boiler will not run properly and you'll be pissed, not to mention broke with a unique lawn ornament.

1 inch isn't considered to be capable of moving more than 90/100,000 btu and the Aspen makes more than that.

 

[ken999]

Check with a heating engineer on the size of the piping you should use in your loop... make sure the pipe is big enough to remove the heat from the boiler to the house. If it's not, the boiler will not run properly and you'll be pissed, not to mention broke with a unique lawn ornament.

1 inch isn't considered to be capable of moving more than 90/100,000 btu and the Aspen makes more than that.

Thanks for the info Leon. It's interesting that some boiler dealers I've talked to were spec'ing 1" tubing for OWB. The 90-100,000 btu number...is that per hour?

 

[LeonMSPT]

We tend to want to assume that those selling and installing boilers and such things know exactly what they're doing on the basic stuff. Unfortunately, especially among the people selling them, it's not always true.

When thinking about piping an add on boiler, there are three big considerations.

1. Distance. How far is it between the boilers. Side by side, or within 20 to 30 ft, maybe 1 inch is "sufficient", or "good enough". I don't know about anybody else. But, if I am spending thousands of dollars on a boiler installation, I don't want "good enough". I want to get as much out of that investment as I can, subject to the rule of diminishing returns. Meaning, at some point spending more money is not going to be worth the investment for the improvement. The smaller the inside diameter of the pipe and the farther the run, the higher the friction head. Flow rates also increased friction head, as the faster you're pushing water through the piping, the higher the instant pressure, which increases friction against the sides of the pipe.

2. How big is it? Is it a 100K unit, or 150K, or 200 or larger? The bigger the boiler, the bigger the piping. Dad, the retired masters oil burner technician and master plumber in the family, never screwed a reducer into a boiler, or reduced the size of the piping, until the heat got to the "destination". Meaning, from the oil burner to the distribution system, the pipe was the same size as the tapping into the boiler. If the boiler has a 1 and 1/2 inch tapping, go with 1 and 1/2 to the supplies for the heating system and hot water heater. Then, reduce appropriately for the demand. Less then 18 feet of finned radiator only "needs" 1/2 inch pipe. Yes, "The Book" says 25 feet... He also had a habit of going a little longer on the radiator sections than called for. If the engineer said 15 ft, he put 18 in where he could.

3. Where will the pipe run? Is it hung on the ceiling, like mine? Or is it buried in the ground, as is commonly done? Is it cold where the pipe will run? Or is is heated space? How much heat loss can you count on through the run and back?

Plenty of people are running on 1 inch pipe, and it's doing the job. One thing I'd hate to see is one more person become sour and have a vendor "take back" a boiler because they were unhappy with it because it "didn't work". Especially when the reason it didn't work was it was hooked up with 100 ft of 1 inch PEX, buried in the ground. Heat loss was minimal between the boilers, it was well insulated. They just couldn't push enough water through the pipe to remove the heat from the boiler. First fire to gassification was great, then shut down on high temp, then within a minute or two, go back to high fire, then back to idle, then back to high fire, then back to idle. There was a river of creosote running out of the thing across the garage floor, and the chimney and heat exchanger was awful.

It's worth doing your homework, is the long and short of it.

 

[LeonMSPT]

Loaded or unloaded, doesn't matter, the temperature in the two boilers is the same, all the time. Only exception is when the wood/coal boiler cools to 140 degrees. Then the circulator shuts off with the aquastat and the oil burner starts.

What I know of storage is learned from the last few months of researching wood boilers and surrounding issues. Put it as close as you can to the oil boiler, then you might use smaller diameter piping between the storage and "destinations". Rules on piping size REALLY important between wood boiler and storage. You want all the heat you can get into the storage to go into it, once the house is satisfied. Hence the use of a temperature sensing valve like a termovar or similar system, to regulate where the water goes.

Cold start, to the house being satisfied, you want all the heat to go into the house, enough at least to make it happy and warm. As the house gets up to temperature and the demand goes down, the heat should be shunted to the storage until that is up to temperature. At that point, depending on the storage capacity and demand, you might let the boiler go out.

During low demand times, summer for domestic hot water and spring /fall, no reason to keep the boiler fired. During dead winter, when it's "darned cold", might want to keep a fire when you're home and leave the storage hot for when you're not going to be home to tend the fire.

Problem with these things is, every system and house is different. Even the same boiler in the same size house, the same distance, is different.

 

[LeonMSPT]

Friction head in PEX, in a nice table.

http://www.cozyheat.net/MTR/tubing/pdf/headloss.pdf

Friction head in copper.

http://www.engineeringtoolbox.com/copper-tubes-heat-capacity-d_476.html

Quote from B&G;website question and answer section...

"For a typical system designed for a 20 degree temperature drop, a 1" pipe can carry about 8 gpm within the normal design range, for a total of 80,000 Btuh."

A "non-typical" system, (i.e. 100 ft of supply and return) it's not hard to wrap one's head around the idea that 1 inch may not be big enough. And then, when about a run away fire? What about when the thing tears off like a rocket? Even if 1 inch is "sufficient" under normal situations, I want extra.

 

[ken999]

Thanks for the info Leon.

I'm a little confused my the info in the link, but I'll try and digest it some more.

When we are talking about a 1" line, does that take into account fittings that recuce the line to 3/4"?, or are we talking about a 1" minimum for the entire line?

 

[LeonMSPT]

The inside diameter of the fitting isn't quite as small as 3/4, but the thinking is sound. The more fittings, the more loss, and that is just one more nail in the box against simpy buying some 1 inch pipe and "going for it". I like a little "extra" capacity with piping. It's only going to work better. Would I connect it with 3 inch if I could get it free? No. Way too much, "extra".

As near as you can to the demand, not less. Especially when it comes to getting heat out of the boiler, more is better.

Only exception is sizing the wood burner. There are those will "Throw the bullshit flag.", and scream from the rooftops to "BUY BIG!", and then "let it roll". Okay, buy big, and let it roll... install a creosote generating smoke machine, because you have to idle it 24/7 except the coldest days of the year. It's your money, your house, your neighborhood, and neighbors. Buy a chimney brush and some rods too, because you're going to need them. Make sure you have your house numbers up per "E-911" so the fire department can find your house easily, although the giant blowtorch coming out of the roof should narrow it down for them. The other option is to open half the windows in the house and leave a load on it. I've done that with mine, just turn the heat up in the basement to keep it from idling too long and cold.

 

[ken999]

I'm hoping that a OWB like the Aspen, parked far enough from the house will keep the fire dept. # out of my speed dial.;-)

I work with a few guys that are big on the Johnsons (don't read that wrong) and Central Boilers, and they are alot cheaper than a Greenwood Aspen or CB E-2300 gasification boilers. The 'normal' jacketed stoves are fine, and I've 22 acres of wood I'm paying taxes on, so ENOUGH cheap wood isn't a consideration...I just want to be sure I'm buying the right thing. It's a big investment. The Johnsons have two fans, baffles and are noted/reputed to be fairly smoke free considering the lack of true secondary burn. I've got two neighbors, one 200 ft away and one 3-400 feet away. Neither should be bothered by a boiler, gasification or not.

I tried having a used Hovel ZK installed (got it cheap) in the basement last fall, and that was/is a fiasco. I don't even want to tell you about it....lol...anyways, my wife and I are getting worn thin by the cold floors, up and down temps, stuffing wood into the PE insert every 4 hours when cold etc. etc. etc. Oh and did I mention we are still buring oil in the Hovel for DHW?...about $3000 in fuel last year. Yeah, so it's time for a OWB.

 

[BrownianHeatingTech]

Piping should be sized correctly.

That means not going too small, but it also means not going too big.

Proper sizing is based upon friction head, as well as flow velocity. A flow which is too slow will allow air bubbles to settle out, instead of keeping them moving along to the air separator.

I really can't count how many systems out there with air problems could have never had those problems if the installer didn't just arbitrarily use some given (large) pipe size, instead of sizing the piping to the actual system.

Joe

 

[LeonMSPT]

Yep, and a flow velocity that is too high won't allow the water to accept the heat from the boiler, not to mention increasing friction head and loss. Decent guideline is look at the outlet and inlet on the boiler... if the people designing the thing didn't think you'd need a pipe that big, they'd have put a smaller one in... it'd be cheaper and easier.

Run the system past a heating engineer before you buy the stuff and install it, not after.

 

[LeonMSPT]

On the piping being "too big", it could be naive... but it seems that it would be easier to make a pipe buried in the ground "smaller" than it would to make it "bigger". Only way I know of to make pipe bigger is to dig it up and replace it, or bury another one just like it beside it. Way expensive, labor intensive, time consuming, and a deal killer for some. Too big? Restrict it, put a short length of the proper size pipe on the return side of the heat exchanger, and you got smaller pipe but could run into problems with air trapping because of slower flow rates. Might make extraordinary efforts to purge air and remove it on an ongoing basis during operation. There are methods and devices that can accomplish removing it on an ongoing basis, but purging during installation remains the biggie.

It's all in designing the system properly, then it works the way it's supposed to unless something is piped wrong, or broken.

 

[ken999]

That's the thing that sticks in my mind. I'm not sure why some dealers are trying to run 1" lines off from 1 1/4" or 1 1/2" fittings. If the manufacture the unit with "x" sized fittings, why reduce? Most likely it's a money thing, trying to save $4/ft on the PEX.

Thanks for the input fellas.

 

[BrownianHeatingTech]

Yep, and a flow velocity that is too high won't allow the water to accept the heat from the boiler...

Just to note, that actually applies to flow rate, not flow velocity. Flow rate is measured in gallons per minute, or cubic feet per minute, or even pounds per minute (or any of a variety of other volume- or mas-related rates). Flow velocity is generally measured in feet per second.

Flow rate is how many cars are on the road; flow velocity is how fast they are driving. On any given size of road, the two will be related, but we're talking about changing the "road size" here, so the difference becomes important. Ten gallons per minute looks a lot different in a 1/2" pipe than it does in a 2" pipe. Just like ten cars per minute looks a lot different on a four-lane road than it does on a one-lane road.

Decent guideline is look at the outlet and inlet on the boiler... if the people designing the thing didn't think you'd need a pipe that big, they'd have put a smaller one in... it'd be cheaper and easier.

Not always. In many cases, certain sizes are "standard," or a boiler block may have multiple uses, or they may design around a worst-case scenario.

That's the thing that sticks in my mind. I'm not sure why some dealers are trying to run 1" lines off from 1 1/4" or 1 1/2" fittings. If the manufacture the unit with "x" sized fittings, why reduce? Most likely it's a money thing, trying to save $4/ft on the PEX.

If the flow rate for the system needs 1" pex, not something larger, then that's what should be used. Using something over-large may cause air to remain trapped, increases heat loss in the piping, and will certainly raise the price to the customer for no reason.

Joe