I'm installing a 360,000BTU outdoor wood/coal boiler. The insulated underground lines will have a run of 230'. I'm planning on using 1" supply and return. Does anyone know if 1" lines will be big enough? My house is around 4300 sq ft and currently is heated with 145,000 BTU propane and has 4 circulators and one that circulates thru the indirect hot water heater.
Newbie question
- Thread starter John148
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
- Status
maple1
Minister of Fire
That seems like awfully small pipe for both the boiler output, and the length of run.
Also seems like a pretty big boiler for the heat load - although don't really know what the heat load is. It will no doubt spend a lot of time idling just from the 1" lines.
Also seems like a pretty big boiler for the heat load - although don't really know what the heat load is. It will no doubt spend a lot of time idling just from the 1" lines.
I have another building I plan on hooking to the boiler at a later date. I also worried about the size of the pipe but plumber said he thought it was big enough. What would you use? I had thought about 1 1/4 pex? Thanks
maple1
Minister of Fire
I'm going to defer to someone else with more knowledge - but from the reading on here, I am thinking that you will be needing a pump on the huge-ish size to get that many BTUs that far through that sized pipe. Which also means an influence on the power bill.
Did your plumber do a head calc? Curious as to what it is. Also curious as to what pump he was planning. And exactly what type of pipe.
Did your plumber do a head calc? Curious as to what it is. Also curious as to what pump he was planning. And exactly what type of pipe.
hobbyheater
Minister of Fire
This is a site that if you don't have OWB maybe you can't join!
http://outdoorwoodfurnaceinfo.com/forum/index.php
http://outdoorwoodfurnaceinfo.com/forum/index.php
Chris Hoskin
TarmSalesGuy
First, find a different plumber. Anyone who thinks that you can move 360,000 btu 460 feet through a one inch line needs to go back to plumbing school. Sorry to be harsh, but we talk to so many people who put in outdoor wood boilers with poorly insulated 1" line and wonder why they can't get heat to the house. Once they've done that, of course, they can't normally afford to just rip out the undersized pipe and re-do it, so they end up over-sizing pumps, etc. to try to overcome the fundamental flaw. I haven't done the math, but I am not even sure 1 1/4" will be big enough for the btu and distance you are thinking about. Second, I would encourage you to think about putting a more efficient boiler indoors in the second building and running the underground lines from there to the house. If the outdoor boiler was splitting the distance between the two buildings, that is less practical and you may want to consider two separate boilers.
Why coal? Are you in PA or lower NY state near the mines so you can get bulk delivery?
Why coal? Are you in PA or lower NY state near the mines so you can get bulk delivery?
I need to check this out closer. I do live in central Pa and have hard coal available. I would be using wood mostly but wanted to be able to burn coal if need be. Thanks everyone for your input. I want to do it right the 1st time.
brant2000
Feeling the Heat
Just some quick back of the napkin calcs indicates that you need to go with much larger than 1" PEX. 360 MBH with a 20 degree delta would require approximately 36 GPM. If you ran a larger delta T, your flow rate would drop proportionally, but 20 degree is probably a good value to assume. Just going off of a quick table I have in front of me, based on flow velocity only, 36 GPM may require 2" pipe.
360,000 BTU input at what efficiency? Some studies show OWF run 40- 45% efficiencies, so if that is data you believe you need to move more like 160- 170,000 BTU/hr. or 16- 17 GPM.
You may be in the 1-1/2" size line. That long length will hurt also.
1-1/2" pex at 15 gpm would have 1.5 psi pressure drop per 100" of run.
maple1
Minister of Fire
The thing is though, the system won't really be moving all the boiler output. It will only be moving what the house uses. (I don't think there is storage planned?). Which leads to the next question - has any heat load calc been done to try to quantify that?
Then the next related thing I see sort of mentioned above - if the system will only be moving what the house can use, there will likely be a LOT of boiler idling. Not sure what can be done about that though, aside from downsizing the boiler or upping the heat load. Or burning frequent small burns - which would likely be a pain.
Then the next related thing I see sort of mentioned above - if the system will only be moving what the house can use, there will likely be a LOT of boiler idling. Not sure what can be done about that though, aside from downsizing the boiler or upping the heat load. Or burning frequent small burns - which would likely be a pain.
brant2000
Feeling the Heat
Although I agree with your statement, I would never want to or recommend anyone install a fired appliance that isn't capable of removing it's rated heat capacity. That's a recipe for disaster.
maple1
Minister of Fire
Well, true, but it seems to be common practice with OWBs. Especially in this case as was planned by the plumber.
Chris Hoskin
TarmSalesGuy
maple1, you are right, the boiler is being sized for the house and a second building. So, assuming that the existing boiler in the house is sized properly, then the peak load there is around 145kbtu/hr..... there is a good chance that the LP boiler is over-sized, however (standard practice). Anyway, it sounds like Bob's 1 1/2" suggestion is about right with the right pump. John148, how big is the other building? How far away is the second building from the house? From the proposed OWB?
The other building is about 150' from the boiler and the building is 36' x 48' with 10' high ceilings and insulated very well. I have only lived at the home, which is a log for a year. Last winter I used 2200 gal of propane and kept the majority of the house at 50 degrees and the area we used at 70. I felt that the propane boiler ran all the time and on the coldest days couldn't even keep the temp at 70. So in short I don't think the propane boiler is big enough?
The dealer I'm planning on buying the wood boiler from has 2 like the one I'm looking at ( 1 heats his business the other his home) and he has his circulator continuously run thru his fuel oil boiler with 1" pex and he claims he has no problems. The plumber said he would T into my existing propane boiler with 1" pex which has 1" supply and return.
So you can see why I'm confused as I have no clue why if the existing boiler has 1" supply and return, whyI would need bigger supply lines from the wood boiler. I had suggested to the dealer I wanted to go with bigger supply and return but he claims I don't need it.
maple1
Minister of Fire
The existing boiler is in the house (I think?).
The wood boiler will be 230' away, with lines in between very subject to heat loss to the ground (and if the ground work & pipe isn't done exactly right you will likely lose half your heat there), and a very signficant pumping head to overcome.
Huge difference.
What is your dealers heat load compared to yours? How far is his boiler from his house? What pump is he using? How much head is it dealing with? How much wood does he use?
EDIT: Plus your feeling that the propane unit ran all the time also indicates you will need to pump a LOT of heat from the OWB to the house.
Is there any way you can move it closer?
The wood boiler will be 230' away, with lines in between very subject to heat loss to the ground (and if the ground work & pipe isn't done exactly right you will likely lose half your heat there), and a very signficant pumping head to overcome.
Huge difference.
What is your dealers heat load compared to yours? How far is his boiler from his house? What pump is he using? How much head is it dealing with? How much wood does he use?
EDIT: Plus your feeling that the propane unit ran all the time also indicates you will need to pump a LOT of heat from the OWB to the house.
Is there any way you can move it closer?
brant2000
Feeling the Heat
Is the existing 1" supply/return copper? 1" copper has a pretty significantly larger capacity than 1" pex, in reality, I believe it is closer to 1-1/4".
Here's a helpful chart...
http://s3.supplyhouse.com/product_files/038-100-W-Flow-Chart.pdf
Here's a helpful chart...
http://s3.supplyhouse.com/product_files/038-100-W-Flow-Chart.pdf
Last edited:
The dealers boiler is 200' from his home. His house is a big old farmhouse. Not sure of the size of his pump? I could move it some what closer but not by more than 50', guessing.
Update... The plumber checked with a local plumbing supply store and they calculated I would need a 0014 circulator to move enough water thru 1" pex lines. I have no clue if that is a big circulator or not. Does that sound right?
maple1
Minister of Fire
maple1
Minister of Fire
I did a bit of googling and napkin scratching.
I'm no pro so would really like to see someone show me what I did wrong.
(This might be a bit backward).
The pump curve I found for the 0014 shows flow going to zero at 23 feet of head.
Your round trip of 460' of 1" pex at 23 feet of head equals head loss of .05/ft.
Another chart I found for Pex head loss shows loss of .05/ft at 5 to 5.3gpm.
To me, all that means that pump won't be able to move more than 5gpm through your loop - at it would be maxed out to move that much. That's not very much. But that's not exact figuring.
Would really like to see their numbers rather than just 'ya it'll work'. How many GPM you will need to heat your house is pretty critical data. If they can't show you calcs they are blowing smoke (even if mine aren't right).
Also, it uses 1.45 amps. Which translates to 175 watts. In 24 hours that's 4.2 kwh. At my rates here, that would be almost $25/month just for that circ. Which may or may not be another consideration.
EDIT: To add from some above figuring already done, 5gpm would only be about 50,000 BTU/hr max. So with everything maxed out with that pump, that is all the heat you would get - that is not accounting for any other head losses (just the pipe), or any heat loss between the boiler & the occupant. Again, very rough calcs.
I'm no pro so would really like to see someone show me what I did wrong.
(This might be a bit backward).
The pump curve I found for the 0014 shows flow going to zero at 23 feet of head.
Your round trip of 460' of 1" pex at 23 feet of head equals head loss of .05/ft.
Another chart I found for Pex head loss shows loss of .05/ft at 5 to 5.3gpm.
To me, all that means that pump won't be able to move more than 5gpm through your loop - at it would be maxed out to move that much. That's not very much. But that's not exact figuring.
Would really like to see their numbers rather than just 'ya it'll work'. How many GPM you will need to heat your house is pretty critical data. If they can't show you calcs they are blowing smoke (even if mine aren't right).
Also, it uses 1.45 amps. Which translates to 175 watts. In 24 hours that's 4.2 kwh. At my rates here, that would be almost $25/month just for that circ. Which may or may not be another consideration.
EDIT: To add from some above figuring already done, 5gpm would only be about 50,000 BTU/hr max. So with everything maxed out with that pump, that is all the heat you would get - that is not accounting for any other head losses (just the pipe), or any heat loss between the boiler & the occupant. Again, very rough calcs.
Last edited:
I'm not sure what numbers they are using. I plan on asking Monday and for the plumber to come and explain to me what he's doing. It worries me that I will invest 15000 and it not work. Thank for the info.
maple1
Minister of Fire
I keep hoping you'll get more number related feedback than just mine - as I said I'm no pro at this. Hopefully you'll get some before Monday.
If you are just heating the house load, maybe 120,000 BTU/hr, taking your boiler input x 80% efficiency. So maybe 11- 12 gpm is what you need to move through thru that 1" pex. Add any fittings and valves to the length of the run, including couplings on that long run
This link tells you, or the plumber, everything you need to know about sizing a circ and piping flow rates. It has all the multipliers for the various pex and copper tube sizes. Run a couple examples and see what a huge difference pipe size makes.
http://s3.supplyhouse.com/manuals/1350986824086/84486_PROD_FILE.pdf
Remember also the power consumption of those high head circs, and the cost to run it 24/7 during the heating season. Yet another reason to size piping to use the smallest possible circ. Also the cost of a 0014 compared to a 007, which could easily move that 12 gpm if the pipe run was sized correctly.
At the end of the day you can always find a pump to move the required load. It's wise to pay attention to flow velocity, power consumption, and expected pump life when they are running off the curve.
Undersizing those underground lines always seem to bite you, numerous posts here over the years have proven the error and expense of that mistake.
ewdudley
Minister of Fire
Just more confirmation of what others are advising, here's a printout for 460 ft of 1.0" and 1.25" PEX (nominal, actual 0.863" and 1.053). Columns are gpm, feet of head, and feet per second.
A 0013 Taco would push about 6.5 gpm through the 1.0" and about 11 gpm through the 1.25", costing about $20 per month 24/7. A 008 Taco would get you a little over 4.0 gpm at about $8 per month 24/7
Once you get up over 3.5 or 4.0 fps flow rate (in your case with 460 ft of pipe), the load curve gets so much more steeper for every additional gpm that pretty soon you can see that there is no affordable solution.
As others have pointed out the flow you need depends on the load you're trying to satisfy and the magnitude of the deltaT you can achieve, not the BTU of the boiler.
As the Taco worksheet shows, deltaT is key in deciding how much flow you need. I didn't catch where it says what your heat emitters are, but if you're stuck with WAHX you can add more coils to get bigger deltaT, and you could add a few radiant panels or radiant floors also to help out.
The 'rule-of-thumb' deltaT is 20 degF, but as the Taco worksheet notes the 20 degF deltaT is more of a worst-case estimating number. With emitter improvements you should be able to get up to 35 degF or more. Actually getting up over 35 degF may be your only option if you're stuck with the 1" lines.
Code:
1.0" 1.25"
gpm head fps head fps
1.00 0.93 0.55 0.35 0.37
2.00 3.34 1.10 1.27 0.74
3.00 7.07 1.65 2.69 1.11
4.00 12.05 2.19 4.57 1.47
5.00 18.20 2.74 6.91 1.84
6.00 25.50 3.29 9.69 2.21
7.00 33.92 3.84 12.88 2.58
8.00 43.42 4.39 16.49 2.95
9.00 53.99 4.94 20.51 3.32
10.00 65.61 5.48 24.92 3.68
11.00 78.27 6.03 29.73 4.05
12.00 91.94 6.58 34.92 4.42
13.00 106.61 7.13 40.49 4.79
14.00 122.27 7.68 46.44 5.16
15.00 138.92 8.23 52.76 5.53
11.00 78.27 6.03 29.73 4.05
12.00 91.94 6.58 34.92 4.42
13.00 106.61 7.13 40.49 4.79
14.00 122.27 7.68 46.44 5.16
15.00 138.92 8.23 52.76 5.53
16.00 156.54 8.78 59.46 5.89
17.00 175.12 9.32 66.51 6.26
18.00 194.65 9.87 73.93 6.63
19.00 215.13 10.42 81.71 7.00
20.00 236.54 10.97 89.84 7.37Once you get up over 3.5 or 4.0 fps flow rate (in your case with 460 ft of pipe), the load curve gets so much more steeper for every additional gpm that pretty soon you can see that there is no affordable solution.
As others have pointed out the flow you need depends on the load you're trying to satisfy and the magnitude of the deltaT you can achieve, not the BTU of the boiler.
As the Taco worksheet shows, deltaT is key in deciding how much flow you need. I didn't catch where it says what your heat emitters are, but if you're stuck with WAHX you can add more coils to get bigger deltaT, and you could add a few radiant panels or radiant floors also to help out.
The 'rule-of-thumb' deltaT is 20 degF, but as the Taco worksheet notes the 20 degF deltaT is more of a worst-case estimating number. With emitter improvements you should be able to get up to 35 degF or more. Actually getting up over 35 degF may be your only option if you're stuck with the 1" lines.
Last edited:
- Status
Similar threads
