Post in 'The Boiler Room - Wood Boilers and Furnaces' started by pulse, Feb 3, 2013.
How many btu's can be effeciently pushed through 1" pex?
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Anywhere from 80,000 to 250,000 btu per hour depending on difference between supply and return temperature.
OK let me refraise my question. How large of a boiler can be used in a shed?
Depends. Is it a metric boiler in a metric shed? Is the area zoned as information-free?
Let me guess...Cozy heat? I have a eko 60 and I can not use it to its full btu rating because of my 1'' logstore If I was to put anything now that i know what i am doing I would do 1 1/4 and spray in foam.. I have to use a big pump to run my water 150' one way A taco 013 where if i went larger pipe i could use a 9 or 10
It depends entirely on the length of the tubing, to and from, and the radiant load at the other end...delta T.
I believe that EWD is trying to show that you haven't given us enough information to give an intelligent answer. The distance of the run and the size of the piping and pump all change the answer.
Sorry, I don't know enough to ask an intelligent question. 150 feet one way 1" logstor, is really all I know. I just don't see how I could supply the house, dhw, and garage at the same time while maintaining boiler protection, let alone have anything left for storage. Just trying to educate myself.
Pulse... Tell us what your thinking/what kind of boiler you want ect. I have a set up like you might be thinking about.
What size house, year built, how much storage you want.
Pulse, didn't mean to offend. If your storage is near your boiler 150 feet from the house, and your house doesn't need all the output of whichever boiler you choose, then at peak your boiler would be putting whatever extra heat you make into storage. All you need to do is figure out how much you need for the house, and if you can get that much through 1" pex, formulas are available to figure this. However if setup is boiler in shed, and storage 150 feet away, (as Taxi's is), then you are trying to push all the heat you make through 1" pex, which is probably possible with a big enough pump and small enough boiler. But not recommended. The possibilities all change with pump size, pipe size, what type of heat emitters you have, and the Delta T that you can achieve. Thats what I meant about intelligent answer, not that you were unintelligent.
Just so you know 1" Logstor is actually 32mm. The I'd is 1.03" which is very close to 1-1/4" pex or 1" alum apex.
Don't worry, no offence taken. Here is the rest of the story. I currently heat my remodeled 3k sq ft home with a conven tial owb. I have been for the last 6 years. I have it working as well as it is going to work. It gets the job done heating my dhw, house and attached 2 place garage. Smoke is a non issue as I am a few years ahead on my wood. I do however use a lot of it though, like 12 +/- cord. I plan on using it for the forseable future but at some point I would like something more effecient. My hope is to be able to use as many of the components of my current system that I can. Just trying to get my ducks in order for some point in the future.
A couple of basics may help you evaluate your problem. 1 BTU is the heat necessary to heat one pound of water 1 degree F. Water weighs 8 pounds per gallon. If you pump 10 gallons per minute, that's 8 pounds of water per gallon times 10 gallons per minute times 60 minutes per hour or 4800 pounds per hour. If you have a 10 degree difference between your supply and return temperatures, that is 48000 BTUH.
More temperature difference = more BTUH, More GPM, bigger pump, = more BTUH. More distance of pipe = more pressure drop and more heat lost in the pipe. More pressure drop = lower flow rate. Larger pipe diameter = less pressure drop. Pipe size say 1" to 1 1/4" dia only affects pressure drop and line losses, so ultimately it only affects pump sizing. Whether you use 1 inch or 1 1/4 inch, if you size the pump to push water at rate you need to get the BTU's you want at the temperature drop you expect, you will be fine.
A couple of cautions. pump sizing can be tricky. Everything in the line, the line, the fittings, the heat exchanger affects pressure drop which determines flow rate in a closed loop. Your ability to harvest the heat affects the temperature drop you can achieve.
Pump and tube sizing starts with knowing the actual load (btu's) that has to be carried. The next step is evaluating your heat emitters in terms of how much temperature drop they will create. Basically speaking, the more temp drop you can create the fewer gallons you have to flow.
Once you get a handle on those two things the tube as well as pump size become a stationary target that is easy to hit.
Where in Michigan are you located?
Well here is what I know with my current setup. The pump on my boiler is a bell and gosset pl30 pushing through 300'(round trip) 1" logstor and pex(inside) to 3 seperate hx's. I also know I need my water to be at least 150* to heat the house.
These delta t's were taken with an ir thermometer so may not be perfect but should be close. The first is a 20plate for my dhw which pulls about 12 degrees, second is a 140K(rated)water/air that pulls 25 degrees. I only keep my garage around 55 so that hx runs very little. I think it is only rated at 40k @ 180*.
My backup heat is a forced air oil burner. On what I would consider a normal winter day (highs) in the 20's, lows in the teen's, my house alone will use 8 gallons of fuel. So if I figure right I come up with 35kbtu/hour for the house.
Like I said, I am happy with everything with my current setup except for the wood consumption. The problem is my owb has made me lazy as far as tending the fire. Now that I am lazy, I refuse to go backwards, meaning I put wood in at 5:00pm and don't do anything with the owb until 9:00 am the next day. So a system requirement for me, is that it has to be able to go for at least 16 hours even during our coldest nights. The other night we were down to -10 most of the night. I have no idea what the btu requirement is at that temp but it has to be more than 35k.
What I want to know is if that is possible with the underground pipe I currently have, using a boiler in a shed and 1000 gallons of storage in the basement. I don't want to go outside at 11:00pm to top off the boiler so it makes it through the night, both for heat and hot showers in the morning! Thanks for any and all comments.
Are the heat exchangers all in series or are they separate loops/individual pumps to each running off your main?
What is the ID of the log store 1" pipe?
Many of these Pex pipes have a 3/4" or 7/8" ID and thus when compared to a 1" ID there is quite a difference.
1" Logstor is actually 32mm. The I'd is 1.03" which is very close to 1-1/4" pex or 1" alum apex.
I know there are many fans if spray in place but I like the very durable outer coating of the Logstor.
Here's what I can deduce from your information. House backup uses 8 gallons of oil at 136,000 btu per gal = 1,088,000 BTU/day.That's about 45K per hour average. I'm assuming that's both heat and hot water on a normal day. Say a normal day average is 15 to 65 degrees or 50 degrees delta T. -10 to 65 would be 75 delta T or 50 percent more demand on average. To get average day heat of one million plus BTUs you need to burn 200 pounds of dry wood at 90 percent efficiency. The buffer storage is effective only over the temperature drop you tolerate. For example 170 to 140 would be 30 degree times 8 lbs per gallon times 1000 gallon or 240,000 BTU's. Assuming you have your storage peaked out before you load at 5pm, then if your total need is 45K per hour then the storage buys you 5 of the 16 you are looking for. The other thing you can deduce is if your average temperature drop in your house heat exchanger is 25 degrees and the average draw is 35000 btu/hour, and since 1 GPM equals 480 pounds per hour, then 35K divided by 25 divided by 480 =3 GPM. These are of course all averages based on your info but it puts you in the ballpark. Hope this helps you evaluate you system and your expectations.
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