Copper or iron pipe for new boiler install?

I'm getting ready to permanently hook up my boiler to the duct coil and would like some opinions. I have 1" iron pipe on hand but the duct coil has 1" copper sweat fittings on it so there is going to be some mismatch no matter what I do. I want to have a bypass loop on the boiler as well for summertime use which is specified at 1 1/4". Copper would be much easier for me to cut and work with. Is it OK to use copper pipe around the boiler for the bypass loop and to and from the heat exchanger or will I lose too much heat?
Another question is with gate valves. I have a bunch of them in various makes and models, Are gate valves all the same? This won't be a steam setup, just hot water, and I'd like to install the valves before and after each component to make servicing them much easier in the future.
Next question is regarding power outages and gravity flow. If we lose power I can keep the boiler hot via hand feeding, the duct coil is about the same height as the top of the boiler so I think water will flow through it naturally. Granted the fan won't be running but if the coil is hot some heat will rise into the house. (better than nothing I think) Do I need a bypass around the Taco 007 circulator pump or will the water flow naturally through it when it's off?
Last question is regarding the domestic (potable) hot water. I plan on running the cold water pipe into one side of the coil and the hot water outlet will Tee into the outlet of the hot water tank. I'm not sure how hot the hot water will be, if it's too hot I'll put a mixing valve in. OR, should I run the hot water into the 40 gallon existing hot water heater tank? There isn't a drain on the bottom of the tank so it isn't going to be easy as far as I understand, it just has a relief valve about 3/4 of the way up the tank. What are the benefits of each way? I'd like to eliminate the tank altogether as it has a 10 year warranty and it's 12 years old so failure is imminent.
Thanks for the help! I'll take pictures and post them when I get started on the install.

Most modern boiler installations are plumbed in copper. The cost of the materials is higher (did not compare prices lately but this is probably still true) but the savings in labor to install usually will see a lower cost to use copper than iron. The heat loss you speak of should not be a factor of any significance.
Many EFMs around here that were installed in the 50's & 60's have a ciculator bypass (with shutoff valve of course). These were not Taco 007s so I don't know if water can flow through a 007 when not running or not, never tried. As you mentioned you can turn your auger by hand to feed the coal and maintain a fire indefinitely, although not as hot as when your blower runs. With power being pretty reliable in my neck of the woods this circulator bypass has become obsolete in later installations.

As "gaw" says, pipe it all in copper. Much easier than cutting pipe tread and less likely to leak. All gate valves are not the same. You want "full flow" type valves. Open the valve and look through it. If the opening in the ball is the same size as the ID of the pipe it is full flow. If you happen to have some that are not full flow use them when the full flow doesn't matter. Like for service drains. I normally use all sweat type fittings. But if I have a tread type valve I'll sweat the threads too. Be sure to take the valve apart when sweating the male adapter. You don't want to heat the plastic seals. I wouldn't recommend this for a novice solderer. I would consider service valves on the circulator. If you want a gravity flow around the circulator I would make the gravity flow path the one with the fewest elbow fittings. The circulator can easily deal with a couple of extra elbows, gravity flow can not. Think through your piping and see if you will need any check valves. Consider the condition when the stove is not working. Will there be convection flow back to your stove coils from whatever is now heating your hot water. Stop this flow with a check valve. Be sure the check valve doesn't negate any safety valve. Good luck.

Yanche wrote: Open the valve and look through it. If the opening in the ball is the same size as the ID of the pipe it is full flow.

Not to be a jerk, but I believe he said gate valve. Yes indeed you'd not want a torch next to a ball valve body since (teflon most common in commercial valves) would melt in no time...yikes!

The gate valves carry no such seals that I'm aware of, more like a wedge shaped guillotine so it shouldn't be to much of a concern.

yes they are gate valves, I've soldered them before with no ill effects, but I go slow. I used to overheat EVERYTHING lol, you don't want to see my first attempts at soldering. I think there are still mounds of solder on the floor. I just priced copper today, sticker shock, $30 for a 10' length of type "L", $35 for 10' of type "M" (which is thinner, but costs more?!?) $1.90 for 10' of CPVC. Can I use CPVC pipe? I could probably sell a couple of the brass gate valves I have and plumb my whole system with CPVC pipe and it's way faster and easier but I always thought that PVC can't take heat.

My mistake. I'm the jerk, need to read and think more before putting typing fingers in gear.

e.alleg wrote: Can I use CPVC pipe?

NO, you can't use any PVC.

Yanche, that's an easy mistake, true gate valves are pretty rare now, the ball valve with a 90* turn handle has replaced the 30-turn handle gate valve. And the ball valve usually seals better.

No you don't want to try to use PVC, but you could use PEX. The cost savings would not be as great.

I'd just buy the copper and get it done. If you have any salvage yards around, copper is a very popular metal to turn in for salvage $$. and often the yards will hold a big pile playing the price fluctuations... so check them out and see if there is some copper pipe that you can salvage from the salvage yard for your piping project... you may save a bundle.

Greg L

It's an academic discussion now, I found a stash of new-old-stock steel pipes already cut and threaded with unions and ells and Tees and stuff in my basement so I used them. Free is good. I doubt they will ever leak, I cleaned the threads and applied high quality pipe dope to the threads and tightened them VERY tight. If I had to cut and thread steel pipe I would pay the money and use copper instead. Woo-hoo! I'm almost done. Big Propane sent me a contract in the mail yesterday so I'm motivated to get this sucker working. They want me to lock-in and commit to buy 2000 gallons between now and May '08 at their "best price" $1.79 otherwise I have to pay truck price of $2.30 or whatever market price is. Once the stoker is hooked up I'll only have to use Propane as a backup and for cooking so a tank should last me a year or better (I'm hoping). $3800 buys a lot of rice coal.

'Big Propane' had to remove three tanks from my farm. A 330, a 500 and a 1000 gallon tank. Left behind a single 250 gallon tank. It sure is small!! I have used about 200 gallons since April, it needs a refill soon. Once the coal boiler is up and running, it will supply the domestic hot water, so my propane use will drop further.

I used to pre-buy around 3-4000 gallons for a winter. And in a cold winter have to buy more. That's a LOT of money, even at prices a few years ago. My current supplier is charging $1.69. It will only go up. At current prices, my winter heat budget would exceed $6000.

You will really enjoy the coal heat. Finding a stash of new unused pipe and fittings was a real bonus!

Greg L