Gas system capacity?

[Coreman73]

I'm trying to check the current gas system in my home to make sure there's enough capacity available to run a couple more lines to an outdoor kitchen space I'm considering having contracted in the near future.

I've got a typical natural gas system supplied at elevated pressure (2 psi) piped in from meter . It runs up to the attic on a 3/4" CSST line and then goes to a regulator, which then supplies four 1/2" lines in parallel. These lines go to a furnace, water heater, stove top and fireplace.

The line to the fireplace is the closest to where the patio is so I'd consider it being the line that would have a tee installed to branch off to the outdoor kitchen.

The only appliance I'm not able to determine the load demand (btuh rating) for is the fireplace. It's a Temco TFC36-3. How could I determine it's load? How are fireplaces considered when an inspector comes out and calculates the full load demand on a gas system?

 

[Jadnashua]

You need to know the inlet BTU ratings for each appliance. THen, you can use tables to determine, based on the size of the pipe, the length, and the number of fittings that change direction, how much of a burner any line can provide. The meter itself often has a tag on it that lists how many BTU it can support, but that assumes your piping after it is adequate. I doubt a 3/4" line coming out of the meter will support another heating device without T-ing off that 3/4" line, but you'd have to do the calculations after adding up the current load and the meter capacity.

 

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[CountryBumkin]

You probably wouldn't have everything running at the same time - so if you're on the low capacity side of the calculation you might still be okay. You have to assume the water heater will/can come on at any time, but most likely you won't be running the furnace or fireplace in the summer (when you are using the outdoor patio kitchen) and you probably won't be using the indoor stove at the same time as the outdoor kitchen/grill.

 

[Dana]

A 3/4" line can move a substantial BTU rate at 2 psi. Your real concern is the capacity of the regulator, and the lower pressure piping after the regulator. The capacity of the downstream regulator may also be lower than the capacity of the meter (something to check.)

I think the TFC36-3 was designed as wood burning fireplace that can also be fitted with a gas burner. The gas burner may be an accessory with a different part number (see if it has one stamped or labeled on it anywhere) which may point you to it's BTU rating. If unmarked, it's likely to be under 50,000 BTU/hr (a 50K /80% efficiency burner can heat my whole house at an outdoor temp of 0F), but probably not less than 20,000 BTU/hr.

 

[Plumber69]

If you have 2 psi your way beyond fine to add what you want. You will need a regulator for each and anything you add. If someone tells me I won't be running everything at the same time cause line is to small... I won't install it

 

[Coreman73]

Thanks for all the replies. My meter is a Rockwell R-275 so 275,000 btuh.

Inlet BTU ratings of appliances:
Furnace - 110,000 btuh
Water heater - 40,000 btuh
Stove top - 36,500 btuh
Fireplace - 50,000 btuh (assuming this at the high end since I can't find any markings at all)
TOTAL - 236,500 btuh

The regulator connected to the 3/4" line from the meter is a Maxitrol 325-5AL model (2psig class I with rating between 7-11" w.c.) that can handle up to a total load capacity of 425,000 btuh.

What would be the preferred way to add the new line? Could it tee off one of the existing 1/2" lines (i.e. line to fireplace) or tee off the main 3/4" line?

Or is the only way to determine this for sure is to do the calculations after I get the run lengths?

 

[Plumber69]

If your 2 psi you can do basically anything you want. Next stage down is where you have to worry. 1/2 will work. Are you doing this yourself? Do you have a gas ticket

 

[Coreman73]

Plumber69, I haven't decided for sure yet if I would be doing this myself or not but am leaning that way. I do not have a gas ticket or any other certification. As a regular homeowner, I believe my city allows residents to do their own work but are not allowed to do anything prior to receiving a permit. Of course, it's required that all work done would be inspected anyway prior to making the gas system "active" again.

 

[Dana]

So, if I understand you correctly, the fireplace is on a dedicated half-inch line, and you want to extend the line to the fireplace out to an outdoor kitchen?

How many total BTUs of burner are you hoping to install in the outdoor kitchen?

Then, how many "equivalent feet" of half inch pipe is there between the regulator and the fireplace (counting all the tees & ells, etc) , and the estimated equivalent feet for the extension? See:

Half inch pipe isn't good for a heluva lot of BTUs post-regulator unless the runs are really short. (I hope the run to the 110K furnace is extremely short.) If it's ~10' (equivalent) from the regulator to the fireplace and you wanted to add another ~50-60K of burner for the kitchen another 15-20' away you could use 3/4" for the extension it should still work OK:

^^^the numbers in the matrix are in 1000s of BTU/hr^^^

If the runs are longer than that or you are planning for more burner than 50-60,000 BTU/hr, you can add another dedicated home run of 3/4" back to the regulator. The regulator has the capacity, but if you put more than 60K out there you may be banging on the limits of the meter if it's all running at once.

If you tee off the 2 psi 3/4" ahead of the regulator with a home-run to the new kitchen you'd have plenty of capacity even with half-inch, but you would need to add a regulator between the 2 psi line and appliances:

FWIW: This is a complete aside, but just in case an equipment swap is coming down the line in the next few years: A 110,000 BTU/hr furnace is sub-optimally oversized for comfort for in your area for homes smaller than ~5000-6000 square feet. Rules of thumb have many exceptions, but typical heat loads of insulated houses in your area run 10-12 BTU/hr per square foot, even for 2x4 framed houses with clear-glass (no lowE) double panes. At 80% efficiency a 110KBTU furnace puts out 88,000 BTU/hr, ASHRAE puts the optimal oversizing factor at 1.4x, so the optimal heat load for the equipment would 88,000/ 1.4= 63,000 BTU/hr @ the 99% outside design temp (=24F, at the Dallas FW airport.) At 1.4x oversizing from the +24F load you're fully covered down to the low single digits for outdoor temp, and the burn cycles are still pretty long & comfortable during normal-cold weather, with less on/off (hot/cold) cycling.

The burner may have been that up-sized if that's what came married to the air handler with the cooling coil sized for the AC or something (?), or maybe for some other reason. Whenever it needs to be swapped out it's a good to get a handle on the true load numbers with a careful Manual-J/Manual-S (using aggressive rather than conservative assumptions), or using a fuel-use against heating degree-day data approach (which is probably better, since it automatically includes all the distribution losses that are hard to capture accurately with a Manual-J.)

With a hot air furnaces there isn't much of an efficiency hit from oversizing, but from a comfort point of view having something that's running more than a 50% duty cycle on the coldest hours of the coldest night of the year, with less of a wind chill (due to somewhat lower air handler cfm) is a big plus. In my area 3-4x oversizing is very common, and though people are usually very reluctant to down-size, those who bother to right-size it are usually glad they did after the fact, due to the enhanced comfort.

 

[Jadnashua]

While only partially relevant, I'm assuming that all of your loads are connected AFTER the current regulator at the meter, so that being 3/4" does affect what's downsteam. The 2psi only comes into play at the meter capacity. You have a 0.5psi system, and all of your calculations, other than the capacity of the meter and the regulator, will then depend on the outlet of the regulator, not the inlet. ONce the pipe gets smaller, the length and number of fittings determine what can be fed from that whole line. Using the chart above, with your 3/4" line at 20' point, you could only draw 160K BTU, and at 30', you can only get 129K BTU out of that line.

 

[Coreman73]

Great post Dana and much appreciated. Lots for me to chew on there.

Jadnashua, yes all loads come after the regulator.

I have more questions but think I need to do some calculations on what I physically have before asking them.

 

[Dana]

With a 3/4" home-run to a ~60,000 BTU kitchen from the regulated low pressure output side of the Maxitrol it's not in capacity trouble until the equivalent length is over 125' .

With a half-inch home run to the 2 psi side it's good for 800' for 60,000 BTU of burner (less something for the length of 2 psi 3/4" from the meter to where you tap in the half-inch, but it's really "who cares?" territory.)

Unless this is some major commercial kitchen type set up it will probably work out to just tap the output side of the Maxitrol with a dedicated 3/4" line, but extending from the fireplace (even with fatter pipe) is less likely, given just how short the half-inch line would have to be.

 

[Plumber69]

If your on a 2 psi system do what you want

 

[Jadnashua]

If I understand what he's talking about...he's talking about not home runs from the regulator, he's talking about one trunk, then branches to multiple devices. There, what you really have is the capacity of the 3/4" line at the 1/2psi, branch it off multiple times to multiple devices, and the 'trunk' now isn't big enough. T everything off the regulator, then each line can run at it's max, but not if you T it down the line. SO, it depends on what, where, and how much you are trying to deliver.