Installing a gas heater questions

What is the CFM of the gas meter?

Post pics of your gas meter showing the data plate.

youmyboyblue said:

"There was a pool heater installed previously, so what you have for the meter and pipe is probably OK."

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I would have zero confidence in this person.

They should know how to calculate the proper size and they should be able to tell you that it is definitely good or definitely not good.

Saying "Probably OK" is not confidence, it is uncertainty.

I would want a gas meter larger then 250CFM for a 250K BTU heater plus other gas appliances possibly running in the house at the same time.

Edit - The given metrics are probably not correct, so the below does not apply unless you can verify the actual metrics.

If you use 125 feet of 1.25" pipe and 355,000 btu/hr, you get 0.50" w.c pressure drop (500 milliinch).

That is 4 milliinches per foot.

(29 feet + 22 feet)= 51 feet is 204 milliinch w.c pressure drop or 0.204" w.c.

For 250,000 btu/hr through a 1" pipe, the pressure drop is about 8.33 milliinch per foot.

For 5 feet of 1.00" pipe at 250,000 btu/hr, you get about 42 milliinch or 0.042" w.c.

The combined pressure drop to the heater is 246 milliinch or 0.246" w.c, which is less than the recommended maximum of 0.500" w.c pressure drop, so the line should be ok based on the given metrics.

Are you sure about these metrics.

I doubt that the lines are copper.

Check with a magnet.

A magnet will not stick to copper, but it will stick to steel.

Also, check the OD with a caliper and match it to the chart.

For example, an OD of 1.315" (33.4 mm) is 1" pipe.

Many people measure the OD and assume that that is the pipe size, but it is not.

Most people measure about 1-1/4" (1.25"/1.315") and assume it is 1.25" pipe, but it is only 1" pipe.

youmyboyblue said:

1.25" outside diameter. The last ~5' where it "T's off" is 1".

Click to expand...

Since you are using OD, those lines are 1" and 3/4".

Also, they are probably steel, not copper.

That is 15 milliinches per foot for 1" line at 350,000 btu/hr.

(29 feet + 22 feet)= 51 feet is 765 milliinch w.c pressure drop or 0.765" w.c.

For 3/4" line at 250,000 btu/hr, that is about 25 milliinch per foot.

5 feet = 125 milliinch or 0.125" w.c.

The total pressure drop is 890 milliinch or 0.890" w.c, which exceeds the recommended maximum of 0.500" w.c.

The manufacturers specify a pressure drop for design of 0.500" w.c.

However, if you have more than 0.500" w.c pressure drop, the appliance should still operate correctly as long as the pressure remains above the minimum pressure specified.

For example, Hayward specifies a minimum inlet pressure of 4.5" w.c.

If you have 7" w.c out of the regulator before the meter, you can have up to 2.5" w.c of pressure drop before the inlet pressure drops below the minimum.

For example, if you have 7" out of the regulator and a 1" drop across the meter, you have 6" after the meter and then if you have another 1" drop across the plumbing, you end up with 5" at the heater inlet during operation, which is above the specified minimum of 4.5".

If you do not follow the manufacturer's recommendations, then they might assume that any problems reported could be associated with low gas pressure and it would become your burden to prove that the gas pressure was always above the specified minimum.

Undersized lines could potentially cause the manufacturer to void any warranty or deny a warranty claim.

Local codes might also address maximum allowable pressure drop for design.

So, while a gas line might work, it is never advisable to use an undersized line.

You probably need new lines and a new meter.

You can go to a 2 psi service if it is available or you can stay with low pressure.

If you increase the pressure before the meter to at least 8" w.c, you might be able to allow a pressure drop up to 3" w.c if your local code allows this.

I just came here to say how great it is to see all the expert level support the TFP team has been providing to the OP.
Outstanding!!

There are different bodies that write codes and local authorities vote on which codes to adopt.

So, your local code dictates things like lines sizing and pressures etc.

Most manufacturers specify a conservative pressure drop for design of 0.5" w.c for a 7" w.c low pressure delivery installation.

If you follow their guidelines, they are much less likely to deny a warranty claim due to low gas pressure unless it is obvious that the gas pressure was too low.

The primary goal is to make sure that the inlet gas pressure never falls below the minimum as specified by the manufacturer.

Any good engineer always adds in margin to any design for safety and I would allow at least 1" of margin for design.

For example, the Hayward Manual specifies a minimum of 4.5", so the minimum design would be to provide at least 5.5" w.c at the inlet.

For example, if you had 8" before the meter and a 1" drop across the meter and a 1" drop through the plumbing, then the pressure at the inlet would be 6", which gives a 1.5" w.c margin.

It is always best and highly recommended to follow all of the manufacturer's installations and by law, you have to follow all local code.

Most service people will automatically flag any undersized plumbing on a heater and either refuse to work on the heater or deny any warranty claims, so it is never a good idea to install a heater with plumbing that is smaller than the installation manual specifies.




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CSA B149.1:20
Natural gas and propane installation code.

The Natural Gas and Propane Installation Code book specifies the maximum allowable pressure drop in a system, based on the system supply pressure.

Gas piping systems with supply pressures:

less than 7″ w.c. (1.75 kPa) must be designed so the pressure drop does not exceed 0.5″ w.c. (125 Pa).

7″ w.c. to 14″ w.c. (1.75 kPa to 3.5 kPa) must be designed so that the pressure drop does not exceed 1″ w.c. (250 Pa).

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2018 INTERNATIONAL FUEL GAS CODE (IFGC) | ICC DIGITAL CODES

402.5 Allowable Pressure Drop

The design pressure loss in any piping system under maximum probable flow conditions, from the point of delivery to the inlet connection of the appliance, shall be such that the supply pressure at the appliance is greater than or equal to the minimum pressure required by the appliance.

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54-18 NATIONAL FUEL GAS CODE ANSI Z223.1

5.4.4 Allowable Pressure Drop. The design pressure loss in any piping system under maximum probable flow conditions, from the point of delivery to the inlet connection of the appliance, shall be such that the supply pressure at the appliance is greater than or equal to the minimum pressure required by the appliance.

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CSA Group was established in 1919 as the Canadian Engineering Standards Association (CESA). It was the first organization in Canada formed exclusively to develop industrial and commercial standards. To better reflect the breadth of CESA's activity, it officially became the Canadian Standards Association (CSA) in 1944 and CSA Group in 2012.