In need of help sizing circulator for homemade boiler

[kentstang]

Where to start.. I've built my boiler out of 1/4 m.s. and I'm just about to the setting out side point of the build. I designed it to hold about 180 gallons water. I think I'm getting lost when I'm reading about total head pressure. Being a sheetmetal worker by trade, hydronics is kind of French to me.
I've bought a 18x20 coil that's supposed to be good for 137,000 btus at 15gpm. I've ran 2-3/4"4supply and return lines to the house that's about 150' of pipe one way. I put foam insulation on all the line and ran them in 6" corrugated pipe about 30" or so down.
Would I be better off if I made it a closed loop system? I'm from central Indiana so our winters don't get to bad for the most part. I appreciate any insight on how I can calculate everything.

 

[hondaracer2oo4]

3/4 pex can only really move up to 4.6 gpm. So with two 3/4 lines each way you are looking at about 9 gpm max. I would just place a t after your pump and feed the lines with a single pump. 150 feet isn’t to bad but you need to account for all the fittings in the system as well. How many btus is your current boiler in your home? I’m just going to throw a dart without doing the actual calc and I would say a grufundos 26-99 3 speed pump will be best for your situation.

 

[hondaracer2oo4]

Here’s the pump curve for a 29-99


https://www.google.com/search?q=26-...gC&biw=768&bih=922&dpr=2#imgrc=rxJoYoju0eCffM:

 

[kentstang]

Currently I have a 80,000 btu LP furnace. I haven't completed the pipework coming off the boiler. I don't know how well it shows up but my supply is in the upper right hand corner. The return goes back in the very front ontop. On that pump does it matter if its a closed or open loop system

 

[maple1]

Not sure what you mean about your pipes. Is that one 3/4" to the house and one coming back? Or two going each way?

By your description I suspect you will be losing a lot of heat to the ground - maybe not right away but moisture will get into your pipe insulation. If I understood you right.

Also not sure what you mean about closed loop. If by your questions you are thinking about pressurizing your boiler - I don't think I would do that, you could be making for a big bang. If your boiler is open and your house system is closed, you will need a heat exchanger to connect one to the other. But if you aren't connecting the systems and the coil your new build is hooked to is only hooked to it, don't seal it up - it doesn't take much pressure to dramatically break something that isn't designed for it.

 

[jebatty]

Design is crucial. 3/4" pex (0.671" ID) even if you are using two 3/4" pex each direction, will be inadequate to move any serious quantity of btu heat. At 300' round trip, pump head (and not including head added by other components in the system), and 3.5 gpm, pump head is about 27' for single 3/4" pex, and at T of 20F, btuh would be about 35,000. Two 3/4" lines in each direction would double that. Now discount that by lower gpm due to additional system pump head, btu losses to the ground, and other unknowns, all lead to total btuh capacity likely to be substantially less. Using a 26-99 is a nice try, but I doubt even that robust circulator can do what you will want or need.

In short, thinking 15 gpm and 137,000 btuh is very wishful and quite erroneous thinking.

 

[hondaracer2oo4]

Batty I agree with you thst he will never be near 15 gpm since he will only be able to move 4.6 gpm through each 3/4 line before headloss gets out of control. If he splits the water between two 3/4 lines each way then he should be able to flow around 9gpm before his head loss gets out of control. A 26-99 will flow this head loss.

I also agree the construction of the underground piping is questionable at best. If you suddenly start losing more than 1 degree each way you know thst the pipes have gotten ground water in them.

 

[kentstang]

This whole deal has kindof been built off the swag method. I didn't know if I pressurized it like 5psi with a relieve valve I could tie my freshwater direct with a backflow preventer.

 

[hondaracer2oo4]

No, don’t pressurize anything unless it has been stamped and certified. I would have to be one confident welder to ever pressurize anything.

Tie freshwater in for what purpose? I am confused.

 

[kentstang]

I was going to tie the freshwater in so that it would stay filled all the time. When I checked for leaks I pumped it up to 30psi. That was enough to get the metal pinging where it was swelling out.

No, don’t pressurize anything unless it has been stamped and certified. I would have to be one confident welder to ever pressurize anything.

Tie freshwater in for what purpose? I am confused.

 

[maple1]

I was going to tie the freshwater in so that it would stay filled all the time. When I checked for leaks I pumped it up to 30psi. That was enough to get the metal pinging where it was swelling out.

You don't want fresh water tied in, or else it will just keep water running out the overflow. You check the level in OWBs, then add water if necessary, like checking oil in a car. Shouldn't be necessary to add any very often at all, unless you have a boil over. I think most go all winter without adding. And the pinging and swelling thing tells you you won't want any pressure on it at all. You might have already stressed things to where it won't take much to go pop.

 

[hondaracer2oo4]

Oh man. Some people like living dangerous! Anyways now that you are still alive let’s move on.

You shouldn’t have to add water more than 1 time per season. You also need to use boiler treatment. Adding new water dilutes the treatment and changes water chemistry. You shouldn’t need to add often. If you want to add water easily just place a t in the boiler return line, add a boiler one way check valve for make up water with a quarter turn valve to add water when needed.

 

[warno]

I would be concerned about the 3/4" lines you talked about running. If they are in the ground already you are sort of stuck with it. I agree with others who've said you will probably run into issues pushing alot of heat through them and also with the insulation factor.

And on the pressurized boiler idea, DON'T. this is coming from a welder who has held pressure vessel certs. If the water jacket is not properly braced with gusseting and stay rods in the right locations it's going to buldge and start breaking seams. With that much flat side paneling it doesn't take much pressure to do damage, as you found out talking about the pinging. Even with a pressure relief valve installed it could still fail. If your relief is faulty you have essentially installed a bomb in your yard. Look up boiler explosions in YouTube, scarey stuff.

Sorry i didn't help any with your original question. Your build looks good though, do you have any other pictures of it?

 

[kentstang]

Heroes how far I've gotten with it sitting on the pad. I'm hoping to have the pump in a couple days.

 

[kentstang]

 

[kentstang]

That's the oldest pictures that i have on this phone ill try digging up others from the beginning

 

[warno]

how many gallons of water is your water jacket?

 

[kentstang]

how many gallons of water is your water jacket?

About 180 gallons

 

[kentstang]

heres how it started with the base and the fire box.

 

[maple1]

Not sure I am seeing things right, but if those are supply & return ports on the back there - they look like they might not be big enough. Which I guess might also explain 3/4" lines you mentioned? Hate to say it but I don't think it would be able to supply much heat if that is the case - plus the 150' one way. Cool looking project though.

 

[kentstang]

The one about 2/3 the way up is the supply. The return goes in up top towards the front. The lowest one is a drain. All 1" nipples I welded on. I'm going to give it a go this season if I need to add more nipples for supply lines ill add them next year in the off season. I should have a long enough cord for the Ole buzz box to reach it.

 

[Bob Rohr]

Here is a wood/biomass boiler built in NY. It takes a lot of stay rods to keep flat sheets together under pressure. You may need to run that as an open, un-pressurized system

 

[kentstang]

Here is a wood/biomass boiler built in NY. It takes a lot of stay rods to keep flat sheets together under pressure. You may need to run that as an open, un-pressurized system

I may have to build another one day and I might have a nice wire feed by then. What would the benefit of a pressurized system be

 

[Bob Rohr]

With a closed pressurized system you eliminate O2 ingress which will corrode any ferrous components. Air removal is easier, higher operating temperatures become possible. You assure NPSH on any centrifugal type pumps, like circulators. Chemical treatments are a one shop deal.

The fill pressure that you put in a system determines how high up you lift the water. So roughly 1/2 psi to lift water 1 foot in elevation. So a 12 psi fill, common in most residential will assure the water reaches a point 24' above the boiler.

The circulator in a closed loop system merely induces flow, over comes the flow resistance in the piping and distribution, it is not liking the water to the top of the system.

 

[warno]

But also keep in mind with everything bob said that a uncertified boiler that is pressurized even with proper gusseting and stay rods is a HUGE liability. If the boiler is not properly pressure tested and stamped for pressurized operation, don't do it. with a home built unit i wouldn't dream of a non vented boiler. A simple 1" vent line is good insurance you won't blow up your house and depending on how close your neighbors house. And even worse potentially harming or killing someone in a boiler explosion. If you want to run a pressurized system and open boiler through a HX of some sort that's fine, but anything with a direct heat input run it as an open system.