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Old 01-20-2011, 12:00 PM   #1
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Flexible gas line for shop heater


Hello,

Just recently built a new house with a workshop attached off the garage. I had the heating contractors run a flexible gas pipe from the basement to the shop ceiling during construction.

I have to do about a 20 foot run of black pipe from the gas supply by the furnace to reach the flexible pipe in the basement. The flexible pipe is 3/4". Should I use 3/4" black pipe as well or is 1/2" sufficient for this?

The guy at the home center that I was talking to about this said not to go from 1/2" to 3/4" but to stay 3/4" all the way.

BTW the the heater is 45,000 BTUs.

One other question here... the exhaust on the heater is 2" and the vent pipe that was installed in the shop is 4", double wall. I am not finding anything at the home center that can adapt. Do they even make a 4" to 2" reducer vent pipe? Not finding anything online either.

Thanks for your help!

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Old 01-20-2011, 02:11 PM   #2
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Flexible gas line for shop heater


Richo,
What kind of flexible line did you have installed? Is it the corragated stainless steel with the yellow jacket? If so, that's ok. I would take a look at the specs for your heater. They usually have a page on gas requirements that will tell you what size pipe to use based on how far you are going. I wouldn't rely on the person at the home center. Not sure on your venting question, haven't seen an exhaust that small. If you have a hvac suppier in the area that sells to the trades, they should be able to fix you up with what you need.
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Old 01-20-2011, 02:27 PM   #3
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Flexible gas line for shop heater


Yes, it is the corrugated pipe with the yellow jacket.

The gas inlet on the heater is for 1/2" pipe. I will check the manual for the heater to see what it says about long runs.

I think what the guy at the home center was referring to had to do with changes in pressure going from 1/2" to 3/4" then back to 1/2" at the heater.

There are HVAC suppliers that I can check with on the venting. I kind of figured it wasn't going to be a common part.

Thanks for your reply.
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Old 01-20-2011, 03:16 PM   #4
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Flexible gas line for shop heater


Is this furnace an 80 or 90% efficient furnace?
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Old 01-20-2011, 03:16 PM   #5
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Flexible gas line for shop heater


"I think what the guy at the home center was referring to had to do with changes in pressure going from 1/2" to 3/4" then back to 1/2" at the heater."
You WILL NOT, under any circumstances get any increase or loss of pressure due to in increase or decrease in piping sizing. You will only change the flow rate, or volume as in Cubic Feet Per Minute (CFPM) with a gas. Pressure will equalize within any differential of piping size as the gas is fed into the pipe or used from the pipe. That's why I do not like the recommendations of employees at the apron stores. Not that I don't like them personally-they are employees and only employees. Yes, you do find the rare one who used to work in the trades and does know one or more particular areas, but seldom.
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Old 01-20-2011, 03:25 PM   #6
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Flexible gas line for shop heater


Quote:
Originally Posted by beenthere View Post
Is this furnace an 80 or 90% efficient furnace?
That I'm not sure about. Is the owner's manual going to say something about that? It's a 10 year old garage heater that hangs from the ceiling.
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Old 01-20-2011, 03:42 PM   #7
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Flexible gas line for shop heater


The owners manual might, the install manual will tell you the vent requirements it has.

Depending on the unit. It may need to vent through SS, not B vent like you have. Some unit heaters that need to be vented through SS, will rot out your B vent if you vent them through it.
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Old 01-20-2011, 03:50 PM   #8
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Flexible gas line for shop heater


I had this heater installed in my shop at my previous home for 10 years and I used dual wall sheet metal piping for the vent, never had a problem with that.

I will have to go back to the same place that I got the venting from back then.
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Old 01-20-2011, 04:13 PM   #9
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Quote:
Originally Posted by Richo View Post
I had this heater installed in my shop at my previous home for 10 years and I used dual wall sheet metal piping for the vent, never had a problem with that.

I will have to go back to the same place that I got the venting from back then.
Remember. We only have the limited info you post, to give our answers.

The more info you give at one time. The better chance of getting accurate answers.
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Old 01-20-2011, 05:15 PM   #10
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Flexible gas line for shop heater


Well the info I'm posting is all of the info I have.

I did grab the installation manual and all it says about gas pipe diameter is that it needs to maintain a line pressure of 7" w.c. and to consult the utility having jurisdiction.

For venting, it is approved for type B-1 double wall vent pipe, which is what I used in the first installation.
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Old 01-20-2011, 05:25 PM   #11
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Flexible gas line for shop heater


Quote:
Originally Posted by Richo View Post
Well the info I'm posting is all of the info I have.

I meant the part that you had it installed in B vent at your other house.

I did grab the installation manual and all it says about gas pipe diameter is that it needs to maintain a line pressure of 7" w.c. and to consult the utility having jurisdiction.

For venting, it is approved for type B-1 double wall vent pipe, which is what I used in the first installation.
How long is the total run from where the flex taps into the gas line to your furnace.

Better to have a larger then you need gas line, then a slightly small one.
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Old 01-20-2011, 05:33 PM   #12
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Flexible gas line for shop heater


There is about 20, maybe 25 feet between the furnace and where the flex line starts. 3/4" makes the most sense I guess since the flex is 3/4" too so I'll plan on going with that.
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Old 01-20-2011, 09:27 PM   #13
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Flexible gas line for shop heater


One quick follow up question: I was reading some info online about gas connections and I came across this on the PG&E website.
Quote:
If you shut off the gas, there may be a considerable delay before PG&E can turn your service on. Once the gas is shut off at the meter, do not try to turn it back on yourself. If the gas service shutoff valve is closed, PG&E or another qualified professional should perform a safety inspection before the gas service is restored and the appliance pilots are lit.
Now I don't have my service through PG&E but how could turning the gas off at the meter prevent you from being able to turn it back on?

When I installed this heater at my previous house 10 years ago I ran all of the gas piping from the basement, through the garage and into the shop. I turned the gas off at the meter to be able to tap into the existing pipe and had no issues getting it back on.

I've never heard of not being able to turn it back on yourself. Is PG&E just wording it that way to discourage someone from turning off the gas except in emergency?
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Old 01-20-2011, 10:56 PM   #14
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Flexible gas line for shop heater


I am sure the gas company is covering its ___.

I am sure that warning is aimed at folks that might not remember to relight pilot lights and check the new work properly.
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Old 01-21-2011, 01:45 AM   #15
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Flexible gas line for shop heater


Wow! I have so many comments on this thread I hardly know where to begin!

To properly size your gas line, you must start at the system reg, NOT where it tees near the furnace. I'll assume that it's an inches set: measure the gas line from the meter to where the farthest appliance is, or will be. This is what will determine the size of your gas piping. Also, you will need to know what size the pipe you are teeing off of is, the max. btuh that each appliance connected to it can consume, and the size of each existing appliance's pipe. All of this info will allow you to properly size your new gas line and ensure that the existing system is large enough for the demand.

PG&E says to call them for relights if you shut-off your meter because they, and most other gas utilities, want to inspect your gas lines because some homeowners think that it's ok to just tap into a gas line and that their will be no problems (imagine that, eh?). The problem with this, aside from poor connections and materials, is that the lines and/or system will be undersized and the connected appliances could be under fired. Under fired=bad! The entire system must be able to sustain all appliances firing at max. rate at once, and all appliances must be commissioned to fire properly by a qualified gas fitter. All of this work should be inspected by a qualified gas fitter, as even a knowledgable homeowner wouldn't have a clue what to look at (or even an old or seasoned tradesman).

If your piping is too small, you will get PRESSURE DROP, and therefore a drop in "the flow rate, or volume as in Cubic Feet Per Minute (CFPM) with a gas." Too large of a pipe will not result in a over pressurization problem, just a larger install bill.

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