Plumbing and Piping - Gas Line Sizing

I currently have a gas furnace installed. It has 3/4" gas line run to a T next to the furnace. The T has 3/4 inlet, with two 1/2" outlets. The furnace is connected to one of the 1/2" outlets. The other is blocked.

I want to install a gas oven. The oven calls for a 1/2" line. Can I simply install the oven using the other side of the T, or does the entire 3/4" line need replaced with a larger size?

3/4" or 1" is usually all that is needed in a residence to supply adequate gas supply. You are working on a low pressure. Using the other T would be fine for the stove. Is there a drip leg at this juncture? Although it is not totally necessary, you may want to replace the T with a 3/4x1/2x1/2x1/2 4 way and install a drip leg on the bottom. Moisture is your worst enemy, and this will help eliminate it.

Hmmm... There is no drip leg anywhere in the system. If I install one, is it simply a small section of pipe that hangs down? Do I ever need to drain the drip leg?

That dead end piece of pipe next to the furnace is a drip leg or more properly known as a sediment trap. In most locals, it is required to be there.

the proper way to tee off the gas line would be to tee off before the shut off valve at the furnace.

most ovens only require a 1/2 inch line, it depends on the btu rating, however the correct way (by the book) is to size your gas lines to make sure your main line is large enough to cover the new cfh your house will have. if you do plan to just use the existing 1/2 inch stub out just be sure that when it is all said and done you are still maintaining adequate gas pressure to all the rest of your appliances: furnace, water heater and anything else gas. typically adding something as large as an oven will require you to turn up the pressure at the diaphram on the gas meter a slight bit to make up for it, using a gas pressure gauge check the inlet psi tap at each gas valve to make sure you have at least 6-7" water column with the valve closed and maintain min. 5" (on the inlet side of course) when the valve opens to ensure that the valve will be able to deliver the correct psi to the manifold its feeding.

I currently have a gas furnace installed. It has 3/4" gas line run to a T next to the furnace. The T has 3/4 inlet, with two 1/2" outlets. The furnace is connected to one of the 1/2" outlets. The other is blocked.

I want to install a gas oven. The oven calls for a 1/2" line. Can I simply install the oven using the other side of the T, or does the entire 3/4" line need replaced with a larger size?

Gas lines have to be calculated by the total load on the line, they can't be eye-balled, it dosen't care what size line you line you have. If you hook this up and it works, fine, but if it dosen't you will have major probs. Lots of luck.

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"If all else fails, read the directions"