0

I'm hoping to install a tankless water heater, and I'm trying to figure out if my current gas meter can handle it. So I'm trying to figure out how much gas my furnace uses.

It's a Goodman GMH950703BXAD. The label says the max temp rise is 69,000 BTU/hour, and the EnergyGuide sticker says it's 98% efficient. Am I right in thinking this means a max gas usage of about 70,500 BTU? (69000 / 98) * 100 = 70408

In response to comments about pipe size, it's 1" pipe coming off the meter. This is about 30', then it reduces to 3/4" at an old unused T, and it's about 25' of 3/4". The furnace and water heater are both at the end of this. So I've already got the required 3/4" gas supply, and it wouldn't be out of the question to extend the 1" line the entire distance if that would help.

  • 1
    I think you can get a larger meter installed by your gas company at no charge to you, if you show you need it. The limiting factor will be what your gas piping can supply. I have an 80 kBTU/h gas furnace and the original WH was a 40 gal tank with burner ~40 kBTU/h. I put in a Bosch Aquastar 125B tankless which draws ~117 kBTU/h and didn't upgrade the gas piping. It may be starved for gas, but works barely. I estimated the limits of our house gas piping and this exceeds it. There is a place I could tap into the largest line from the meter, but so far have not done so. – Jim Stewart Feb 1 '17 at 8:56
  • The absolute most you would have to do is to connect another 3/4" line at the T you report at the place where the 1" line changes to 3/4". If you would do this with iron pipe it seems to me that you would want to put in an additional capped T to make it easier if later someone wanted gas for a gas range. What size of water heater are you installing in kBTU/h? – Jim Stewart Feb 2 '17 at 19:43
  • It's a 200 kBTU/H heater – Drew Feb 2 '17 at 19:44
  • It seems to me that to get full function you would want a separate 3/4" line from the T, and this would be sufficient. You could go through the calculations of 30' of 1" carrying 270 kBTU/h followed by 25' of 3/4" carrying 200 kBTU/h and see what the tables say. Some of these 200 kBTU/h heaters have specs accepting lower inlet pressures than others. I guess they have designed burner and regulator to allow this. What is the winter climate where you are? How cold is the incoming water? – Jim Stewart Feb 2 '17 at 19:54
  • Denver, so cold but not ridiculously so. Incoming water is about 50 degrees. – Drew Feb 2 '17 at 20:08
1

The gas meter usually is not the problem it is the gas line either through the house or the connection size and the size of the line you install. A minimum 3/4" gas line to the new water heater is required. And the line you pipe into should be at least 1 inch. Any thing smaller and you will not have enough gas flow. The main gas line in the house should be at least 1 inch. You could call the gas company and see if they can raise the gas pressure to your house. 8 ounces used to be the maximum.

  • The gas line coming into our slab on grade house is 1" (actual OD 1.3"). This goes up into the attic and at some point transitions down and divides into a 3/4" line (actual OD 1.05") into the furnace/water heater closet, and another line which goes to the fireplace. At this point there is a capped nipple which the builder inserted to allow a line to be added for a gas range. In the heater closet the 3/4" line divides into two short 1/2" lines (OD 0.84" ), one to furnace and one to water heater. This is probably barely adequate for our minimal tankless heater, but not for a 200 kBTU/h model. – Jim Stewart Feb 1 '17 at 12:27
  • I thought about connecting a 3/4" line from the capped nipple in the attic to supply the tankless water heater, but just decided to try the existing line. Our hot water supply is adequate for two retired people, but might not be adequate for an active family with children in the house. The normal American lifestyle would require at least 200 kBTU/h to allow for multiple simultaneous uses of hot water. – Jim Stewart Feb 1 '17 at 12:38
  • The meter our gas company supplies us with gas at about 7 inch water column (7" WC) which is 0.25 psi. The company reportedly will supply a different type of meter or different pressure reducer which will deliver gas at higher pressures I think 2 psi and 5 psi. I haven't seen any such meters as I walk down alleys near my house, but maybe I wouldn't recognize them. The appliances in the house would have to have different pressure regulators than the ones in place now because notices on the furnace and water heater limit the allowed inlet pressure to something like 8" or 10" WC. – Jim Stewart Feb 1 '17 at 13:13
  • @d-george I've added some info on the pipe sizing to the question. It's 1" and 3/4" all the way to the heater. – Drew Feb 2 '17 at 2:31
  • I would run the 1" pipe all the way to above each appliance and then add a 1x1x3/4 tee to drop down to each device. (that is a 3/4" line to each appliance). So the above horizontal line would be 1" and each drop down would be 3/4". The drop down (vertical) gas line for the furnace could be 1/2" if you so desire, but if I were doing it, it would be 3/4". I would also contact the gas company to be sure that they can supply the gas you will need. I'm sure its okay but I would still make the call. – d.george Feb 2 '17 at 11:07
0

To get full function you would want a separate 3/4" line from the T at the end of the 1" line, and this would be sufficient. You could go through the calculations of 30' of 1" carrying 270 kBTU/h followed by 25' of 3/4" carrying 200 kBTU/h and see what the tables say. Some of these 200 kBTU/h heaters have specs accepting lower inlet pressures than others.

The standard meter connected to a 1" line will supply 270 kBTU/h.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.