Undersized feed to stove?

boris2

I have recently installed a new natural gas range. Its being fed by the same 1/2" pipe as my old stove. Only thing really different than my old stove is that has that center burner and an extra "power burner".

I noticed after I installed it, the manufacture suggest a 3/4" pipe for the supply and that "smaller pipe may result in insufficient gas supply". It appears to work correctly though, there is solid blue flame on all the burners, no yellow whatsoever and I dont see any dimished flame height as I put on all the burners even with my furnace and water heater running at the same time.

However, if I calculate the BTU requirements for the stove and compare it to the gas sizing chart using the longest run method I am falling short on the 1/2" btu (providing I calculated correctly).

This happens when I calculate all the burners, broiler and oven btus from the nameplate on the appliance. However, if cheat a bit I can make the numbers work... for example, the combined BTU's include both the oven and broiler (both of which cannot be turned on at the same time). So that drops my btu requirement further. Their is a center burner as well that is never used in conjunction with the stove and other burners... that drops me further. That drops my btu requirment right at the maximum allowed on the chart.

I still thought I should have a plumber look at it and I had a guy out for an estimate to repipe that section and he said he had never installed a 3/4" pipe feeding a standard range in a residence like I have. That it would be overkill and that he wouldnt go to the trouble and expense if everything is working properly as its very rare you would use the entire btu ratings on the nameplate of the stove. However, since the manufacture suggests a 3/4" pipe he can change it if I like. It would cost more than the stove itself to do this.


FWIW: Here is what I calculated:

Stove is farthest appliance from meter. Its 78K btu counting everything on the nameplate. The stovetop is 51K alone. My meter is 250K with a regulator rated at 5"-7" wc. Its more than I need for my gas usage which also includes a furnace (70K) and WH (40K). The main trunk from the meter is 1". Also more than I need for my service.... 3/4 would suffice.

The stove is located 60' from the meter.... 1" trunk runs about 54' and then there is a 1/2" branch to the stove for 6'. It is that 6' that is undersized. I added 50 percent for fittings which I think is the correct formula so a total run of 90'? I think if the 50 percent extra for the fitting factor is not added then their is not much of an issue at all.


Should I open a can of worms to replace that 6' section of 1/2" pipe?

mattmia2

1. The code specifies all the loads that can be used simultaneously, so if the broiler and bake burner can't be on at the same time you would take the maximum of those.(some newer ovens fire both for faster preheat so make sure that doesn't happen). If the power burner and the other burners are interlocked so they can't fire at the same time you would take the total of the higher collection of those groups, not the sum of both groups.
2. The low pressure gas pipe sizing table is for 1/2" WC(water column) pressure drop. In most cases a higher drop is acceptable to still provide the minimum inlet pressure for the appliance.
3. The way to test it would be to fire all the appliances on high at once and measure the inlet pressure to the appliances with a manometer and verify that you have above the minimum nameplate pressure at the appliance.
4. You can divide that run to the stove in to sections. You can calculate the pressure drop on the 1" section then calculate the drop on the 1/2" section. Since that 1/2" section is so short I doubt the total drop will be 1/2" WC.

boris2

thank you for the response.

Is adding 50 percent to the total length for fitting factor the right way to calculate?

Would there be a visual indication by flame height or color if my supply was inadequate?

Are the btu's on the nameplate exact? I read that burner rating vs actual output is quite different. ... am I further cheating by thinking I am not getting full btu ratings out of that pipe anyway?

pecmsg

If the IOM calls for 3/4" then that's what's needed to meet the minimum code.

boris2

I understand that but I am not trying to pass an inspection. Am I barking up the wrong tree asking here?

pecmsg

boris2 said:

I understand that but I am not trying to pass an inspection. Am I barking up the wrong tree asking here?

God forbid there's a fire and a following investigation what are you going to say then?

Even work done by homeowners MUST meet minimum standards. in your case the manufacture wants X,Y,Z. Your responsible as the installer to meet those requirements.

JUGHNE

The IOM suggests 3/4", they cannot know the full piping situation. Only the 6' of 1/2" is on the small size.
Again this is figuring all burners are firing......seldom happening IMO.
To put this in perspective, the stove uses more gas than your furnace, that is a lot of heat in one room. It would probably keep the furnace from running if the thermostat were close.

We have a 5 burner gas cook top and never have had all burning on high at one time, not enough room for big pots.

You should however be concerned about a good exhaust hood vented to the outside.

boris2

Bottom line, do I have a safety concern here in your opinion? Or am I crunching numbers and worrying for nothing?

boris2

Is running gas thru a pipe at its maximum chart rating dangerous?

ethicalpaul

My simpleton's take: I mean, if the maximum rating were dangerous, it wouldn't be on the chart. The chart would be lower, below the danger point.

More likely, the maximum rating has a built in safety factor and is plenty safe.

mattmia2

The chart is a 1/2" water column pressure drop chart. In most situations the methods using the chart perform extremely conservative calculations. If you want to confirm the pipe sizing, get the fuel gas code and perform one of the mathematical calculation methods.

If the instructions require 3/4", that can most likely be accomplished with a reducer and a 3/4" gas connector, assuming one of the calculation methods from the code shows the pressure at the appliance will be adequate. You also need to calculate the loss in the piping shared by the other appliances to do a less conservative calculation.

ChrisJ

I'm not an expert but I've never heard of sizing a gas line by the connector on an appliance. Just because it has a 3/4" connector doesn't mean 1/2" isn't enough or that 3/4" is enough, it could need 1 1/4" if it's long enough with a lot of turns.

I would go by the calculated length my self. I've never heard of adding 50% for fittings, but rather using the equivalent lengths for each type of fitting.

A 6' long 1/2" line with a few fittings is good for an awful lot of natural gas.

If you wanted to be extra safe you could have a combustion analysis done as well and as @JUGHNE said a good quality outdoor vented exhaust fan should always be used.

You also said you had a professional come out and look at it and in his opinion everything was good.

boris2

How would the stove work if its starved? What if any indication would i see if i had a problem?

Leon82

Turn it all on high and see if the burner flame maintains the same as only one burner on

boris2

Fwiw, I think the suggestion of "use 3/4 supply because smaller size MAY cause insufficient gas size is just in the whirlpool/maytag manuals.... i saw a few others install manuals from other manufactures, some for stoves with higher btu ratings than mine, that specify either 1/2 or 3/4 supply.

I doubt the salesmen at the lowes or their installers ever mention that caveat when selling or installing whirlpool made stoves. Theres gotta be millions of them hooked up to 1/2 pipe.

Leon82

My stove has some sort of regulator looking device on the gas line after it branches off the main line. So the length of regulated pipe is much shorter that the run.

I'm not sure if yours is the same

JUGHNE

I do not believe you have a safety concern.

The worst thing about that short length of slightly undersized pipe would be a slight drop in gas pressure at the range.

If this were a complex appliance where gas pressure was critical then there might be a concern. IMO

You have fired all the burners, oven??, the furnace and water heater and see no diminishing of the flame height.

You have a 1" main running around the house, what size of pipe branches off that to the furnace (same btu's as the stove) and off to the water heater (probably 1/2 load of the furnace).
Those branches could be only 1/2" and maybe longer than 6'.

All of these appliances have a built in gas pressure regulator that allows the inlet pressure to vary somewhat and still deliver the required lower pressure to the burners....all of them.

There are at least 2 methods to compute pipe sizes for loads and distance. They both do not necessary agree.
I have seen 20' of 1/2" connected to a 1" main operate a 100,000 btu furnace. It has been that way for 30 years.

BillyO

if you have an Italian grandmother I bet all burners are firing at same time with broiler and oven!!!! lets not assume guys

boris2

How exactly do i count fitting into total length?

I saw one method to count each one after the first 4 which are ready factored in. And then i saw another where you add 50 percent.




Also in regards to btu output, i read something online that says it rare for a stove burner to actually put out the btus on the label... that it could be as much as 1/2 less.... is that true as well?

ChrisJ

> @boris2 said:
> How exactly do i count fitting into total length?
>
> I saw one method to count each one after the first 4 which are ready factored in. And then i saw another where you add 50 percent.
>
>
>
>
> Also in regards to btu output, i read something online that says it rare for a stove burner to actually put out the btus on the label... that it could be as much as 1/2 less.... is that true as well?

Here's an example
https://www.engineeringtoolbox.com/resistance-equivalent-length-d_192.html

boris2

From the same webpage:
https://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html

This one shows a ratio 1:5 which I have been calculating as length of pipe + 50% of length of pipe = total length.

boris2

There was another one that says the first 4 fittings are already factored into the chart. Perhaps I am confusing different methods.

ChrisJ

boris2 said:

There was another one that says the first 4 fittings are already factored into the chart. Perhaps I am confusing different methods.

How many fittings does the 1/2" pipe have and what kind?

boris2

The entire run is 60' from meter to stove.
54' of that is main trunk and is oversized to 1".
the branch to the appliance is 1/2" and is 6' long. It has a total of 2 90s, 1T and a 45.

I assume I also have to count the fittings on the 1" trunk as well.

It doesnt matter because any way I crunch it, I fall short because of that 6' section of 1/2" pipe. However, I really dont know what I should do because I dont see low flames or yellow flames. there is no way I would ever have all the burners going at high at once either. Even with the furnace and and water heater running the flames really dont seem to flinch. But because folks say Carbon Monoxide is the silent killer, I dont know... maybe their isnt a visual indication when there is a problem?

Jellis

6 Feet of 1/2" pipe can flow over 100,000BTU of natural gas at 3.5"WC

Your pressure is higher than that and your stove is under 100K btu requirement.

if you turn on EVERY burner on your stove and they all have acceptable flame then you are all good.

JUGHNE

Boris2, I believed you answered your own question:
With all the gas running in the house, the burners do not waver;
You will seldom ever run all the stove burners on high;

See what Jellis said above.

You should have a CO detector on each floor.

You should have a range hood vented outside.

EBEBRATT-Ed

@boris2

Your fine leave it as is. There are 2 ways to size gas pipe If you use the branch method the 1/2" only has to carry the stove btus for a distance of 6'.

Just make sure you have no leaks and you are fine....no safety issue

Solid_Fuel_Man

Manometer to check manifold pressure while everything is lit/on is the best way.

I agree that the charts size for 1/2" pressure drop and are usually one pipe size larger than would be minimum.

If the incoming gas pressure is above the minimum required by the appliance with all loads on then you have adaquite pipe diameter.

The chart is usually very conservative.