Help! Can current setup support 250k btu heater?

styopr

Getting so many conflicting answers! My 17-year-old Pentair 200k BTU MasterTemp pool heater died, and I hope to replace it with a 250k BTU unit, same brand. I think I have 2 PSI coming into the house, stepped down from 5 PSI provided by the gas company. The regulator is stamped with a red 2# on the cap, though the meter is white. There are 2# regulators in front of all appliances (heater, gas fireplaces, water heater, pool heater). The line to the current 200k BTU heater (about 35 feet) is 1/2 inch. My question: should this support the 250k BTU model based on the current setup?

HomerJSmith

More photos from further away would be helpful. I would suspect that the pressure from the street to the meter is in the range of 30 to 45 psi for NG. The meter regulator reduces the pressure to about 7"WC. (Water/Column)

The pressure loss from the meter to the appliance depends upon the length, size, and fittings on the pipe or how many BTUs that can be reasonably be delivered to the appliance. Altitude above sea level also impacts fuel delivery to the burners.

1/2" Plastic line from the street to the meter isn't uncommon. Delivery of NG is dependent upon two things, pressure and pressure loss. Increasing the pressure in the gas valve can make up for 50K BTU increase in the boiler, easily.

There are appliances that have regulators attached to them, but I am surprised that all your appliances have regulators attached to them.

I would like to understand more about your situation. Photos further away and more of them would be helpful. Your altitude, location, and age of your building, too.

mattmia2

That looks like it might be 1/2" od copper or polyethylene which is more like 3/8" id. If your house is a 2 psi system is can probably do it but you have to do the math for that line and for all the other lines to make sure there isn't too much pressure drop in the common piping by the meter or combined drop out to any of the line regulators at the appliances.

styopr

Ok @mattmia2 I think you are correct probably nominal 1/2 PE (I measured .527) with an approximate ID of around 0.4 inches. According IFGC 2018 Appendix A:

For 1/2 inch OD (0.4 inch ID) PE Pipe at 2 PSI:

• Length: 40 feet
• Capacity: Approximately 284,000 BTU/hour

Given this information, the capacity for a 1/2 inch OD (0.4 inch ID) PE pipe at 2 PSI over 40 feet should still be around 284,000 BTU/hour. Since it was already supporting 200k BTU without any problem, should be accurate or close to it.

mattmia2

You also need to make sure the shared piping at the meter can support the combined load and still have enough pressure after the combined drop of the shared piping and the piping out to your other appliances.

since you probably need about 5" wc at the appliances the total pressure drop can probably be more than the 1psi in the table.

styopr

@mattmia2 Yep - that's why I opted not to do the upgrade! Just replacing it with the same (200k btu). It was originally specked out for that and has been operational without issue for 17 years… 250k seemed to be right at the margin, so decided to stick with a known!

HomerJSmith

"The devil you know is always better than the devil you don't know." Which is why boilers are always replaced by looking at the name plate rating of the old boiler as to sizing regardless of whether the old one was over sized. Hopefully, sizing is done better on the new replacement. Hydronics is an improving science.

How do you even know that you need 250K or that you even need 200K. There are many factors that determine a boiler's size. Supply water temp, the amount of heat emitters, pump sizing, heat loss, etc. It's a balancing game. Do the math, it's simple.

Conclusion, I need a 150K boiler.

mattmia2

With a pool it is a lot more about how fast do you want it to heat up than about calculating the heat loss.

HomerJSmith

Sorry, I forgot it was a pool heater.