tankless water heater questions

[JosephP]

Thinking of upgrading (?) to a tankless water heater (possibly this one which is the same as this Rheem unit).

Couple of installation questions:
1)  Advertising says you can use existing 1/2" supply.  Installation literature says 3/4" gas supply (page 53).  We have a 3/4" line that comes into the utility room then splits into (2) 1/2" feeds for the furnace and existing water heater.  No other gas appliances.  Any reason I couldn't make that 3/4" to water heater?...will it short-change the furnace?  (I assume I need to confirm how much gas the meter lets through by checking with the gas company...)

2)  Current water lines come out of the wall above the water heater tank.  I'm guessing that in the long run, I'm better off cutting into the wall and putting an elbow lower in those to feed this from the bottom as opposed to looping those down from above?

3)  For the condensate drain:  currently, the A/C condensate drain goes into the sump hole.  Should I send this there too?  Or is it wiser to cut into the nearest drain in the crawl space and put a T in there to accept this and the A/C condensate drain (and the overflow for the heater)?  (also of note:  it says do not put a trap in the drain...I assume that is because it because there typically won't be enough water?  But does that sound like a bad idea to anybody else to let sewer gas creep into the utility room...or is there an internal trap in the unit???)

4)  For the vent and air intake, I'm thinking I'd use a Concentric Vent Kit.  Mostly so I can only have to poke 1 hole in the house.  Given the choice, would you go straight up about 12-15' through the roof or through a wall which would take it up about 6' into the attic and then 30' horizontal run?  (the nearest gabled end - which puts me just short of the longest acceptable run with 3" pipe)

Anything else I need to be aware of or asking???

[photobug]

I wanted to put in tankless since I built my home 20 years ago.  I finally had to replace my old electric.  I looked at the tankless and factored in the cold ground water and to evaluate if it was feasible.  Unless I put two tankless heaters in my home would potentially suffer a loss of water pressure as a result of the water heater's limitations.

In the end it was the need to clean out the heat exchanger as a result of hard water.  Since the water hardness is off the chart where i live and the ground water is so cold in winter, I opted for a powered exhaust gas water heater instead.

If you have already thought it through and the tankless is going to work with you.  Here are some answers.

1. You will need to pressure test your gas to see if there is enough pressure to power both the waterheater and furnace will have enough pressure to run both.

2. Changing the plumbing will be cleaner but probably won't make a big difference.

3. No clue

4. Did you factor in a 90 degree bend in your pipe length computation for the horizontal route?

  Given a choice I would have liked to go straight through the roof, the right piping and plumbing would allow you to put other options of water heaters in the future as opposed to needing a powered exhaust.  I chose to go through the wall because I didn't want to do the roofing myself and paying the roofer fees was offset by the cost of the more expensive but more efficient water heater.

[JosephP]

....
In the end it was the need to clean out the heat exchanger as a result of hard water.  Since the water hardness is off the chart where i live and the ground water is so cold in winter, I opted for a powered exhaust gas water heater instead.

If you have already thought it through and the tankless is going to work with you.  Here are some answers.

1. You will need to pressure test your gas to see if there is enough pressure to power both the waterheater and furnace will have enough pressure to run both.
.......

They have a chart in the product literature about maximum amounts for each common mineral.  We are on city water, so they'll have that data.  That is on my to do list.

1.   Do I need to hire a plumber to do the pressure test or will gas company (Columbia) do that  OR will a $10 gauge adequately tell me what I need to know?  Do CFMs matter or just pressure?


PS: I think I got part of my answer to #3...  Looking at other heaters of the same brand, they do require a bed for a water trap, so I'm going to assume there is a trap inside the unit I linked above.  Still curious about best place to drain the water.

PPS:  Interesting as I'm looking at the second unit linked in this post...it is $200 cheaper, but it seems like much of that savings will be eaten up in the need for steel concentric vent pipe for the full length of the vent.  Cheaper isn't always cheaper.

[carwashguy]

1)  Advertising says you can use existing 1/2" supply.  Installation literature says 3/4" gas supply (page 53).  We have a 3/4" line that comes into the utility room then splits into (2) 1/2" feeds for the furnace and existing water heater.  No other gas appliances.  Any reason I couldn't make that 3/4" to water heater?...will it short-change the furnace?  (I assume I need to confirm how much gas the meter lets through by checking with the gas company...)

When I was checking out tankless units I found an online calculator that you added up all of your BTU requirements and it gave you the pipe size required.  Turned out that the tankless water heater would put me about 100K BTU over what my supply line would allow.  I have gas stove, gas water heater, gas furnace and gas dryer.

[jamesglenn]

All of the above is good information. You need to calculate the total BTU consumption to know what size gas line is required, and the size of the unit is based on the number of items using hot water.

I replaced a oil fired water heater with a tankless propane gas heater back in 2009. I looked at doing it myself, but in the end hired a plumber with knowledge. It took two guys 10hrs to remove the old and install the new. I have a concentric vent kit thru the wall, runs about 20' and with (3) 90degree elbows, it's at the limit. The shortest vent route is the best for horizontal runs.

I would caution that if you have hard water or sand, basically if you have a well, then you'll need to treat the water before the heater or it will destroy it. I have hard water and sand so with a softner and whole house filter, the heater has lasted and doing well.

Understand that they do not provide instant hot water when the faucet is turned on, it takes up to a minute depending on the distance from the unit. I would advise installing a recirculation pump with a line to the farthest point possible and that will provide instant hot water. 

I personally love my unit and will never go back to a tank model, it saves money and does provide seemingly endless hot water when running.

[JosephP]

....
Understand that they do not provide instant hot water when the faucet is turned on, it takes up to a minute depending on the distance from the unit. I would advise installing a recirculation pump with a line to the farthest point possible and that will provide instant hot water. 
.....

What is the additional lag time caused by this type of heater?  As it is, it takes +/-30 seconds for our bathroom to heat up - just because of the distance from the water heater has to pass the cold water out of the pipes first...

Recirculating pump would be nice...but adds a couple hundred...Though I see a Westinghouse unit that has a recirculater built in for about the same money (and more GPM).

[jamesglenn]

What is the additional lag time caused by this type of heater?  As it is, it takes +/-30 seconds for our bathroom to heat up - just because of the distance from the water heater has to pass the cold water out of the pipes first...

Recirculating pump would be nice...but adds a couple hundred...Though I see a Westinghouse unit that has a recirculater built in for about the same money (and more GPM).

It takes mine about 60 seconds it seems on average to get hot water to the upstairs sink or shower. That is when the recirc pump is not programmed to be on. 
I have a Navian propane unit that has a built in recirc and a programmable control unit for it. When programmed to be on with recirc, it takes 10secs maybe at the same location, and that is to clear the water in the pipe. Mine was a retrofit, so my return line is only in the basement to as far as possible.

Stick with units that allow pvc vent piping and the concentric vent. 

My plumber sized the gas line I would need as part of the install and changed out the existing for a larger 1" line.

My condensate line goes to a condensate pump that is shared with the furnace and then pumps into a sanitary line.

[photobug]

Understand that they do not provide instant hot water when the faucet is turned on, it takes up to a minute depending on the distance from the unit. I would advise installing a recirculation pump with a line to the farthest point possible and that will provide instant hot water. 

I would ask about some professionals about this at least with a tankless.  Doing this with a tankless eliminates the advantage of having a tankless.  The tankless does not heat and store hot water but just turns on when hot water is asked for.  If you put a recirc pump on the tankless you are essentially leaving it on and using the pipes in your house as a storage tank.  The only way I can see this being a good idea is if you put a timer on the recirculation pump and use it only for very short windows of high demand.

The cold water lag for a tankless would be the same for a tanked heater plus a small lag for the heater to engage.  Beware of "cold water sandwiches" from cheaper models.

I would double check the math on this water heater, by the time you pay to install it, it might not save you any money over the long haul compared to a high end, high efficiency storage tank heater.  You will probably need a plumber to test the gas pressure, as it is not like the water system that you can just put a valve on an outside spicket.

Check out The Rinai Guy on Youtube.  He is a New Yorker moved to Fla that does installs of these for a living and was willing to help me out when I asked.  He also has a woodworking channel also.

In the end it did not make financial sense for me to install a tankless water heater.  I am not against making bad financial decisions for something I believe in it was having to hire someone else and pay them a lot of money to make that decision that me go another way.  I think if you live in a warm climate without hard water where plumbing labor is available and at a reasonable rate, tankless heaters make sense.

[jamesglenn]

The only way I can see this being a good idea is if you put a timer on the recirculation pump and use it only for very short windows of high demand.

This is exactly how my unit works. It's on for 2hrs in the morning and 3.5hrs in the evening. Rest of the day is hangs on the wall using a small amount of electricity to power the control unit (timer, temp setting, clock).

I would also recommend looking into tax rebates if you go with a high efficiency unit (tank or tankless) I received 30% in taxes on unit and labor.

[JosephP]

It probably won't pay for itself. But it will make a lot more room in the utility room... And it would give endless hot water. Not a frequent problem... actually changing that may cost us more in water and using more hot water than we otherwise would. Not a math problem - a fee hundred over 10-15 years for a lot of convenience isn't much $.