Gas plumbing

[RTK]

I'd like to install a tankless water heater and a gas clothes dryer but I've never worked with gas lines before and I don't know if my plan will be within code. I have a conventional gas water heater right now and it is encased in a small closet in the hall adjacent to the bathroom. I want to knock out the closet to make room for a washer and dryer. The new water heater will go in the same spot as the old one. The dryer will be four feet away from the water heater. I don't know what the rules are for venting these appliances or if I can have a gas dryer in the middle of the house. I've never worked with gas lines so this is new to me. My house is old and used to be heated by gas wall heaters and a floor heater, now it has central air and heat. The old wall heaters have been capped off and removed, so it seems logical to use these old lines to tie in the new dryer (assuming the lines are big enough). Will my plan work? What do I need to know to safely do this job? What tools will I need?

[LazyPup]

Your project presents a number of problems to be considered.

First of all, you state that your water heater is presently in a closet adjacent to the bathroom and you plan to knock the closet out to open a space for your water heater and laundry. That is fine providing you are not opening the space into the bathroom. Code prohibits installing a solid, liquid or gaseous-fueled water heater in a bedroom, bathroom or a room that opens into a bedroom or bathroom.

In order to insure that the burners will not cause oxygen depletion in the livnig space need to determine if the room will be a “confined space” or an “Un-confined space” To do so we must first know the BTU rating of all burners in the room. A confined space is any room that has equal to or less than 50cu.ft per 1Kbtu/hr.

Per the code table a gas laundry dryer is typically rated at 35,000BTU. On the other hand a tankless water heater rivals a central furnace for gas consumption. By example I have checked the specs on three popular gas fired tankless water heaters.

Bosch AquaStor Tankless…………… 117,000BTU/hr
Takagi T-K2…………………………..185,000BTU/hr
Paloma PA28R………………………...199,900BTU/hr

If we were to choose the lesser of the three, the Bosch AquaStor we would then have a combined combustion load for the laundry area:

Tankless water heater……117,000BTU
Laundry Dryer…………… 35,000BTU
Total 152,000BTU (152Kbtu)

Allowing 50cu.ft for each 1k/btu = 50cu.ft x 152K/btu = 7600cu.ft
Allowing an 8’ ceiling we would then get 7600cu,ft / 8’ = 950sq.ft
We could then estimate the minimum room size by finding the square root of 950sq.ft
Thus if these two appliances were installed in a room smaller than 30’x30’ or equivalent it would be defined as a confined space.

By contrast, if you were to select the Paloma PA28R we would get:
Paloma PA28R………………… 199,900BTU/hr
Laundry dryer………………….. 35,000BTU/hr
Total 203,400BTU/hr (203.4Kbtu/hr)

50cu.ft/1Kbtu x 203.4Kbtu = 10,170cu.ft (room volume)
10,170cu.ft / 8’ ceiling = 1,271.25sq.ft
Again using the square root to estimate equals a room 35.65’ x 35.65’ or equivalent.

Obviously your closet space will be somewhat smaller than an unconfined space so we must now consider providing additional combustion air. One option is to install ducts through the wall to an adjacent unconfined space. When doing this we must install two ducts, one 12” down from the ceiling and a second one 12” up from the floor. Each duct must provide 1sq.in for each 1kbtu/hr but not less than 100sq.in.

In the case of the Paloma tankless the ducts would need to provide 204sq.in. (14”x 14” grilles).

A second option would be to install ducting down from the attic space. The attic must have a minimum of a 30’ vertical rise at the peak of the roof and each duct must provide 1sq.in for each 4kbtu/hr

204btu/hr divided by 4kbtu/hr = 51sq.in cross sectional area. (two 9” diameter round ducts from the attic space.) The ducts to the attic space must be sleeved through the ceiling into the attic space until the ducts are 6” above the attic floor.
Having resolved the mounting location we must now compute the size of the gas line.

The first step is to determine how many cubic feet of gas per hour you will require. Properly you should contact your local gas supplier and find out the BTU per cubic foot equivalent for the gas they supply. When that information is not available the code gives us a figure of 1100BTU/hr per cubic foot.

Previously we determined that the lesser of the three tankless combined with the dryer would require 152Kbtu/hr thus it would be 152,000btu/hr divided 1100btu/hr = 138.1cu.ft/hr while the large water heater & dryer would require 203,400 /1100= 184.9cu.ft/hr.

The likelihood of being able to use the existing gas lines is slim to none. Typically the existing gas lines are ½” and ¾” pipe.

The maximum cubic footage of gas that a ½” line can convey is 95cu.ft for a distance not to exceed 10’ of pipe.

A ¾” line could convey up to 200cu.ft for a distance not to exceed 30’ of pipe but keep in mind that we would also have to factor in any other burners connected to that line.

Thus if the developed length of pipe from the gas meter to your laundry location exceeds 30’ you would need to install a dedicated 1” line (not to exceed 100 feet of pipe.)

[JCA1]

Most Demand water heaters are direct vent.

I'd say the existing gas lines will in no way be adequate fpr a tankless unit. I'd also say that you having no experience with gas piping, you should seek professional help.