Suggestions for New Plumbing for Remote Boiler - With Pics

I think as long as you are not going from 1 1/2" to an 1" back to 1 1/2" you should be fine. My radiant system goes from 3/4" to 1 1/4" to 3/4" and it works perfectly other then the fact it's powered by oil.
I would just watch out to make sure you are not over heating the pex pipe or have it to close to the boiler.

Adamiscold, Thanks for the reply. I also think it will be alright. But I still have a 5% doubt in my mind.
Maybe with all the twists and turns the water has to do around the boiler(causing water friction/turbulance) it would be better to bump it up to 1 1/4"

Can anyone else give an opinion on this?

The nominal ID of PEX-AL-PEX one inch tubing is 0.98". The nominal ID of 1 inch type M copper tubing is 1.055". So it's a good match. If I understand your desire the coal boiler will be remotely located and the water piped via PEX-AL-PEX to your existing boiler area. I would use 1" copper on the coal boiler supply and return lines. Use copper everywhere. Use copper male adapters threaded into the boiler tapings. Use compression PEX to copper fittings.

On the existing boiler side of the run, I don't have enough of an understanding of what you want to do. Boilers in series, parallel, manual water flow switch over, automatic switch over, parallel-secondary loop, etc?

I also don't know your heat distribution piping, 3/4" basboard, radiators, zone circulators, zone valves, single returns, common returns, any radiant manifold, injection mixing pumps, on and on?

I would strive to switch existing supply and return piping to copper. The piping resistance of elbows, tees, valves are expressed in equivalent of pipe lengths. Analysis is very similar to that of series and parallel electric resistor elements. The electrical analogy is linear, Resistance = Voltage / Current. The piping flow analogy is not linear. Piping resistance (feet of head) = fluid constant x hydraulic piping resistance x flow rate raised to the 1.75 power.

Quote from Yanche - "On the existing boiler side of the run, I don't have enough of an understanding of what you want to do. Boilers in series, parallel, manual water flow switch over, automatic switch over, parallel-secondary loop, etc?

I also don't know your heat distribution piping, 3/4" basboard, radiators, zone circulators, zone valves, single returns, common returns, any radiant manifold, injection mixing pumps, on and on?"

Yanche,
Thank you so much for the reply and help. I hope this post isn't to long. This project is driving me crazy but I think I'm almost there. I'm planing on puting the boilers in series (they are about 90' apart). Please take a look at the pictures I posted in the beginning post. I'm going to move the pump from the return on the oil boiler to after the exp tank because of what I've learned here(pumping away) I think for now, I will run that pump (the existing pump, a taco 007) constantly to keep things simple. After water leaves that pump it will go to a flo check (I'll reuse the one in the picture) about 10X pipe diam downstream. Then it will loop up and back to meet up with the Pex return to the coal boiler. Suppy from the coal boiler will enter at the return for the oil boiler, a big series loop, also my primary loop. I think I should tap into this loop after the flow chek and before it gets to the return pex with a secondary loop for the house radiators. 2 closely spaced T's with a taco 007 IFC(with flo check)on the supply side and a swing check before it meets back up with the primary. I'm thinking I'll have the circ pump run power from both boilers go to a relay and then either boilers thermostat can turn on the house circ pump (I'll set the oil t-stat lower than the coal t-stat for backup). My whole house has only 1 zone with 1 pump at the boiler inlet now going to 12 large old radiators fed by various sizes of iron pipes, some are up to 2". It branches out to 2 pipes on the supply side and returns back in 4 pipes on the return (you can see them in the picture), very simple control but it works just fine. I'm going to try and use the DHW coil in the oil boiler as long as I can keep the oil boiler from kicking on. If it draws too much heat two quickly and even with a large aquastat differential between the 2 boilers the oil kicks on, I'll probably route the output of the DHW coil to the inlet of the electric heater to help it.
I'm glad you said 1" copper would be good at the coal boiler.
Based on my description of the system:
1. Whould it also be acceptable for the rest of the primary loop at the oil boiler to be 1" copper? and
2. Would it be acceptable to make the beginning and end of the secondary loop 1" copper till it joins the house iron pipes?
3. Does my relay idea make sense for the t-stat control of both boilers?

The price jump to 1 1/4" copper is substantial when you add up all the isolation valves, pipes, fitings etc. Hundreds of dollars more. If I don't need it, I don't want to waste the money.

I think I'm almost there, finally. Your expertise would be very much appreciated for these last few concerns

The bottom line here is that you're using 1" Pex coming from the garage. It wouldn't matter if you use 4" everyplace else, you will only get the heat that can be flowed through the one inch. As Yanche suggested, go ahead & use one inch around the boiler.

Just today I read a couple of things. One: Based on a 20 degree temperature drop one gallon per minute will comfortably transport 10,000 BTU/hour. Two: The flow rate of 1" copper or iron pipe is about 8 GPM. 1 1/4" is 14 GPM. So, you're able to move about 80,000 BTU per hour. I'll venture a guess and say as long as you weren't burning 1,700 gallons of oil a year, you'll be fine. I guess if you come up short when it's 30 below zero either the oil will kick in, or you'll need a more powerful pump.

I'm sorry I still can't make a recommendation on pipe sizing for the additions to your existing boiler piping. I've re-read all your posts here's what I suggest.

1. Pipe your coal boiler with 1" copper at the coal boiler and use 1" PEX-Al-PEX to get it's supply and returns into your home.

2a. Hire a heating contractor to design and install the rest.

OR

2b. Buy this book.

http://www.hydronicpros.com/publications/index.php?id=24

Don't flinch about the $125+ price, it's worth every penny. It's the only book you will need. Read, study and understand the principles. This will take weeks of effort. Apply this understanding to your unique situation.

3. If you don't want to do 2a. or 2b., just leave everything as is except to pipe the coal boiler in series with your existing boiler using 1" copper. It will work (with considerable inefficiencies), but you will get heat at lower cost than now. Be sure to re-size your expansion tank or add a second one. See 2b. on how to size it.

Freddy, Yanche,
You guys give excellent advice, Thank you. We do(did) use alot of oil per year, about 1300 gal. in our 125 year old poorly insulated 3400 sq. ft. farmhouse (with making DHW). When I went to the plumbing store yesterday I just couldn't bring myself to buy all the 1 1/4" copper knowing it was attaching to 1" pex. I also couldn't bring myself to buy 1" copper to put it from the 1"pex to the 1 1/2" return side of my 180K BTU oil boiler(in series). It would probably work ok but I'm not getting the warm fuzzies about it. I have been reading the Modern Hydronics book, a great book.

OK. Some more research to do, including talking to and getting a couple estimates from heating contractors to have both boilers feeding separately into a primary loop with modern controls etc. etc.. I've got 101 other things to worry about just like you all. I'm about at the end of my time limit on this one.
Thank you, BG