Natural Gas line needed for Heater replacement

[texflood]

Hi all - first time poster, long time lurker.

We moved into a house in MN about a year and a half ago that has been our first experience with pool ownership in the summer and giant ice cube in the winter. Down right balmy today in the mid 50's! Much thanks to everyone for all the helpful information on here, it has been tremendously helpful in learning the ropes!

Last fall the original (I believe) 1997 Minimax heater died so we are now in the market for a replacement. So using the thought process that bigger is better for heaters I began looking into a 400k BTU Raypak replacement. I talked to Centerpoint and they were able to get me slated for an upsized meter at no charge, I just need to coordinate a gas company to reconnect gas into the house because they don't do that. Great, no prob. I called a gas company that does a lot of pool work to check out the natural gas line that runs out to the pool. They validated that I currently have a 2 stage setup with roughly 125' of 1/2" line running to the heater. They said with my current set up they recommend replacing with a 206k BTU heater because a 250k heater is pushing the current setup. But I could try for a 250k BTU heater knowing that it may have problems. I think they lean towards being conservative which is fine with me, they are the experts. However, to accommodate the bigger heater, they would need to run 170' of 3/4" line around the pool to the heater. Unfortunately this pipe would undoubtedly become a problem when we want to do any landscaping/planting trees/changing fence line in the future. And that is the shortest run without attempting to go under the 15' long patio cement right that would be the best direct line to the heater.

Anything off with any of these numbers for the gas line?

So with this info I started going down the line of possibly moving the pool equipment pad since it is currently situated in the middle of the lawn and moving it to behind the garage would allow for a gas line to easily be run through the unfinished basement. I had the pool store service tech out and give me some numbers to move the pad and they were ballparking somewhere around $5,000 to move the pad about 25 feet! Unfortunately this is probably the type of pricing to expect in this area for the pool stores as there is not a lot of options. And I paid $100 for them to come out and take a look...

So with that info I found a pool guy who doesn't have a storefront, is not mostly hot tub focused, and seems to know his stuff as he has been in the business since the 80s. I felt confident with him when he said he does all repiping in 2" pipe, recommended a Raypak heater, talked about hydraulics, etc. He quoted me $2500 to move the pool equipment. If I were to leave the equipment he quoted a 250k BTU Raypak heater for $2500 installed, but he said the gas regulator at the heater should be replaced with a larger version - I think it may have been a 7" pancake valve but could be wrong on that.

I'm now leaning towards the 250k replacement option as it helps contain the expenses. Should I expect that a new heater will give more output than a 1997 model due to efficiency improvements or will I experience similar performance?

 

[BoDarville]

Welcome to TFP!


Sounds to me like the second person you spoke with is the more knowledgeable of the two with regard to the gas pipe sizing. Given the length of the run you are talking about, 2” piping makes more sense. The 3/4” pipe the first guy suggested seems too small, especially given the 170 foot run they suggested - I seriously doubt that it would run a 250K BTU heater. As a reference, I have a 1.25” line run to my 400K BTU heater and the run from the meter to the heater is about 40-45 feet, including two 90° elbow bends near the equipment pad.

I’ve done some work on gas & propane lines in the past, so I’ll pass along a key point with regard to pipe sizing. The BTU capacity of a gas line is dependent on the pipe diameter, run length, fittings used along that path, gas pressure after the meter (although, in a [single-stage NG setup] residential environment, that is tightly controlled within a range of between 5 and 7 inches of water column - in PSI, this is between 0.18 and 0.25 PSI), and elbow bends. When a pipe's inside diameter is doubled, the area of the pipe increases by a factor of 4, not 2 as most would assume. The increase in BTU capacity is even greater – about 4 to 6 times - depending on the length of the run as well as the other factors mentioned above. The point is, each incremental increase in pipe diameter makes a big difference in the BTU capacity of the pipe.

With all of that said, my only concern with the second “pool guy” that has “been in the business since the 80s” is how much of that experience is with natural gas lines, how knowledgeable he is on the current codes, and whether he is licensed. Although he seems like he knows what he is talking about when it comes to pipe sizing, I would vet out his natural gas code creds a bit more.

As for the efficiency of a new heater compared to a 1997 model, odds are that it will be more efficient but it depends on the specific model. The efficiency of most heaters today are rated in terms of AFUE - Annual Fuel Utilization Efficiency. As an example, a brand new 2015 250K BTU heater with an AFUE of 90% and a 1997 250K BTU heater rated as 75% AFUE will still burn 250K BTU per hour. The efficiency is related to the % of those 250K BTUs that go towards heating the pool vs. how much is lost to exhaust. So even with a more efficient heater, the gross BTU’s of these units is the same...250K. The gross BTU's is the determining factor as to pipe sizing (re-plumb or new construction) or determining whether the currently installed pipes have the capacity to supply the unit with enough gas.

 

[texflood]

Wow, lots of great info in your second and fourth paragraphs, thank you for that info as I hadn't seen a lot of that in my searching! ;

I should clarify more about the the first guy. He is licensed and does the work for at least one pool store. The second guy is more of a pool builder/renovator, not licensed in gas. I have a 2 stage setup so I believe I have 2psi from the road to the meter then stepped down to the 1/2" line running from the meter to the pool heater and that was running the old 250k BTU w/o issue. He is now suggesting the that line to the pool to be 3/4" which looks to be the right size for a 2 stage setup at this long of a length. He is coming back out on Friday to hook up my meter after Centerpoint puts in the bigger meter to hook my gas to the house back up so I'm going to try to see if there are alternative runs that could be more cost effective for my situation...

The thing that concerns me about putting in a new Raypak 266k BTU cupro nickel heater is that my heat output will not really increase much from what I had (due to the cupro nickel vs increased efficiency) which would be a bit of a bummer...

 

[JayBauman]

The BTU capacity of a gas line is dependent on the pipe diameter, run length, fittings used along that path, gas pressure after the meter (although, in a residential environment, that is tightly controlled within a range of between 5 and 7 inches of water column - in PSI, this is between 0.18 and 0.25 PSI), and elbow bends. [/I]

This is not true, in the context of the OP's text. What you have described is correct for a single-stage setup, but codes and practices have been updated to allow 2-stage gas delivery for outside utilities due to the impractical nature of needing larger and larger diameter gas lines as the need for BTU/hr increased.

In his post, OP states he has a 2-stage setup. In such a configuration, the gas supply to the house goes from delivery pressure (~50lbs) to 2 lbs in the first stage and from 2 lbs. to 5 oz. in the 2nd stage. The run to the pool will come off of the 2 lb. section, where it will be reduced to 5 oz. with a pancake regulator very near to the heater.

While a 2-stage setup will give higher BTU/hr at the outdoor appliance than a single stage setup, I cannot comment on whether the existing pipe can carry enough gas for the heater to run correctly. Your gas company can (and will, if you ask) tell you what you'll need to run your equipment. And since they only want to sell you gas (and not make money on a plumbing installation), their recommendation will be unbiased. Give them a call if you want to get a 2nd opinion on what your options are.

 

[BoDarville]

Correct, what I posted about the water column is for single stage - which is what I have worked on in the past. However, this does underscore what I mentioned about making sure that whoever works on your (or anyone's) setup is up to speed on current local codes and holds a valid license to work on natural gas lines in your location as codes can vary from one location to another.

 

[texflood]

Absolutely agree that this should be handled by a licensed professional. Thanks for the explanations as that helps me to understand what the heck is needed. I started all this thinking I could just disconnect the old heater and put in a shiny new Raypak 400k BTU heater.

Regarding the pancake regulator at the heater - the second guy (pool builder) seemed to think that replacing the regulator with a larger one would help to get more gas to the heater. I'll have to ask the gas guy that on Friday to see if that is a possibility.

 

[BoDarville]

Something to keep in mind if you are giving serious consideration to going with a new pipe run...While you've got the gas guy there, it wouldn't hurt to inquire about going with piping large enough to handle a 400K BTU heater. He will be able to tell you if there are any other concerns with that aside from cost considerations. The time to ask these questions is while he is there and before any ground is broken and/or you purchase a new heater. It's always good to have all your options laid out before making a final decision.

 

[JayBauman]

Regarding the pancake regulator at the heater - the second guy (pool builder) seemed to think that replacing the regulator with a larger one would help to get more gas to the heater. I'll have to ask the gas guy that on Friday to see if that is a possibility.

A larger regulator can allow more BTU/hr, but you're still limited to what the existing line can deliver to the regulator. Please keep us apprised of your learnings. I know I'm very interested to see how this one turns out.

 

[texflood]

On Friday, Centerpoint installed a bigger meter and the gas contractor came and reconnected the service to our house so that much has been completed. With the contractor, we talked through the two best options for running the new line.

First option, from the meter into the basement through the unfinished area of our basement and out the back of the house. Second option, from the meter underground but with a 20' run under the concrete patio slab in our backyard (he estimates will cost ~$300-$400 for a third party to do that bit) so a total length of 125' for $1500 total. He charges $10 a foot underground.

Both options are 3/4" pipe as that is what the charts dictate and the gas contractor noted that they try to minimize the number of 90" turns to help the flow rate. I'll post more details when the time comes to run a line since that will help me know where the lines are buried for future reference.

I'll give more results in a few weeks. Have to now hire a landscape contractor to level an area behind the garage and put in a small retaining wall so that the pool guy can lay a new pad for the equipment pad. It is 52 degrees F here today so the swimsuits are staying in the closet for awhile!

 

[ps0303]

I have hooked up many Raypak 400K units on 3/4" @ 120' plus. Raypak's are the most forgiving units in this aspect.

 

[JamesW]

A 3/4" first stage high-pressure (2-psig) line should be good for 400,000 BTUs up to 150 feet of straight pipe. I would suggest considering 90s as equivalent to 4.5 feet of straight pipe. For example, using five 90s would be equivalent to adding 22.5 feet of straight pipe. 125 feet + 22.5 feet = 147.5 feet.

If there will be more than five 90s, I would suggest going up one pipe size. In any case, make sure that all local codes and manufacturer specs are followed.

 

[JayBauman]

Hi James. Those approximates are valid for liquid flows. For compressed air (which would approximate 2 lb. natural gas), a 90 bend is equivalent to about a 1ft. length, and a 90 elbow is about a 1.5 ft. length equivalent. I think the OP should be just fine with the recommended setup.

 

[JamesW]

Hi James. Those approximates are valid for liquid flows. For compressed air (which would approximate 2 lb. natural gas), a 90 bend is equivalent to about a 1ft. length, and a 90 elbow is about a 1.5 ft. length equivalent. I think the OP should be just fine with the recommended setup.

OK, thanks for the clarification.