I am consider installing a tankless water heater. The gas line that goes to my current hot water tank is a 1/2 inch galvanized drop from a 3/4 line in the attic. This 3/4 line seems to come off a reducer coupling from the main supply line that is at least a 1.4 inch size. The unit I am considering (as seems most) requires a 3/4 gas inlet pipe connection. I am above average in the skills area but I am a little concerned at what is required to loosen the union connections in the attic with regards to the pipe length, in order to up-size the drop pipe to 3/4. The house is about 20 years old and the connections look very solid. Are there any tips or tricks anyone could suggest.

Unless it is where it was damp and rusted, gas pipe usually isn't too bad to get apart for the DIY. It is not like limed, rusted water pipe. Coughing up for a 24'' pipe wrench or 2 would almost guarantee success. I have made do with Vise Grips and 16'' Channellocks. If worst comes to worst, you only need to unscrew the reducer. The old small pipe will yield to a Sawsall or even an abrasive disk in a portable circular saw. Surely what is there, and certainly what you want to use, is black iron not galvanized. Some places you can use copper or maybe the right plastic. Anything but galvanized. The plating can flake off and cause big trouble. About pipe sizes, ID. Some fittings even have the size marked on them. 3/4'' OD stuff is really 1/2''.

Do a search here, and you will find I have my doubts about tankless heaters. I looked into them and decided they wouldn't solve any of my problems or save much money. You might get more interest putting the difference in the bank than what you would save on gas. In the summer my whole gas bill with base charge, hot water, and a gas drier is less that what the tankless hype says I would save. If you can't take advantage of the size to move it closer to the point of use, you will still wait just as long for the instant hot water to get to the faucet. The unit may be small, but the required clearances add up to as much room as a tank. They also have a minimum flow rate. Not good if you only need a small stream.

I leave much of the plumbing to Tom, but thought you needed assurance from another DIY on the pipe.

Thanks labman! I was thinking along that route with the vice grips but what DIY would turn down a reason to buy some new tools huh!! Do the tankless heaters require thermal expansion tanks as the tanked heaters? Also would you think it is more feasible to install an outside unit with easier access to the gas line and re-route the water pipes. Or a garage installation near previous tank connections but then having to install the venting system with about a 8 foot horizontal run?

You will not be heating a closed volume of water and so should not need an expansion tank. I can't say the code isn't written in such a way as to still demand it.

I would put the tank as close to the most frequent point of use, inside or outside. As I said, you will still have a line full of cold water to run out before getting any hot water.

If the old tank made do with an 8' horizontal run, likely the new one would too. Does the installation manual give the limit from the code? The new vent may have to be much bigger.

The old current venting is the smaller standard size used with the older tank I have now. It has the roof vent set up. The horizontal venting I spoke of was to be the tankless manufacture recommended larger stainless steel type.

Yes, in all cases, the directions are much more reliable than me.

I mentioned 2 pipe wrenches, but did not explain the importance of the second one. You put a wrench, vice-grips, etc. on a pipe and turn, the nearest joint may or may not unscrew. Use you best wrench to hold beyond the joint from turning.

Great! Thanks for the very useful information labman. I have taken detailed notes and will surely put them to use. :)