View Full Version : What would cause this?
HVAC/Stud
09-05-2013, 07:07 PM
Two story house two full baths up stairs, one full on first floor. The house had two 40 ga water heaters. I removed the two tanks and added one NG tankless water heater, 9.8 gal capacity.
There was a SO valve between the two tanks that I opened. Every hot water tap when turned on has 118 degree water.
The problem is when the upstairs shower is being used its fine, untill someone is using the downstairs shower at the same time. The upstairs will go cold.
I'm a HVAC tech, any guidance from my fellow trades?
Thanks,
Cris
Big Hoff
09-05-2013, 11:18 PM
Did you test with the SO closed again, sounds like that was there as a bypass and now you might not have adequate flow to upstairs when both are open. Does the downstairs shower have hot water when both are being used?
HVAC_Marc
09-05-2013, 11:35 PM
What is an SO valve?
Remember that a rating of 9.8 GPM is at a specific temperature rise AND is rated in a laboratory setting. You need to know the temperature of the incoming water, the set temperature, and the maximum flow of all the most likely simultaneously used outlets of hot water. Only then can you determine if you have enough capacity.
It sounds like you don't for the flow of those 2 showers. 2 tanks may have been required by code if there is a spa/tub/jacuzzi in that house. If there is not enough capacity you may need 2 or more tankless units.
VTP99
09-06-2013, 12:52 AM
Shut Off valve.
HVAC/Stud
09-06-2013, 07:41 AM
thank you all so much for the response I am going to investigate some more
ControlsInMT
09-06-2013, 08:45 AM
What is the gpm of the two showerheads?
HVAC_Marc
09-06-2013, 10:21 AM
Shut Off valve.
Duh, why didnt that occur to me... :gah:
Aircooled81
09-15-2013, 12:07 PM
Is there a resirc loop involved here? Pressure drop through a tankless water heater may be greater than the drop through a resirc loop, and if the pump is not running, water takes the path of least resitance and cold make-up water wanders back through the resirc loop to the furthest point (possibly upstairs bath)
A valve between the original water heaters could be a few things. I would love to here if it was between the the domestic hot water water into the house, or if it was configured to just isolate the two water heaters from each other. Can you describe the piping arrangement, were both water heaters manifolded together, or do the hot sides of the original water heaters disappear into the house on their own?
It is very unlikely they have 2 4.5 gallon shower heads. As far as cold water upstairs, cold water comes from the cold side of a single handle shower valve, so if the pressure drop on the hot side is greater than the pressure drop on the cold side, hot water can't win the race. What if this has something to due with the shower valve rather than the loop... Does this happen at two handle faucet upstairs too? Hook a pressure gauge up to the angle stops on the upstairs faucet, turn on the hot water downstairs and see if the upstairs hot water pressure drops far below the cold water side.
If pressure drop is the issue, then we can discuss another round of options.
good luck, hope some of these ideas help.
also, regardless, let us know what the solution was.
wsm0807
10-08-2013, 09:51 AM
Is it a two family house? If so maybe you combined two separate dhw systems and now, assuming similar pressure drop in the shower valves, the hot water is taking the path of least resistance (first floor). Thats the only way I see two 40 gallon water heaters making sense
Sent from my SPH-L710
GilliganHVAC
11-16-2013, 10:29 AM
TanklessTankless Tankless thats all I here anymore from my clients as they have been brain washed by green energy. Lets face it "They are NOT green" The cost is high, the maintenance is high, they save very little fuel and on an installation like this one they don't produce enough flow as the restrictors will slow the flow to maintain the water temp. We pull out more tankless heaters as they are never sized properly like this one.The upper floor shower loses pressure as the lower floor uses water. The restrictor reduces flow to maintain temp and the lower floor gets the pressure and the upper starves due to the height gradient. A total load calc of hot water is needed and the heaters need to be at mid flow as they don"t produce volume at full flow. I'm sorry for all of the work of installing a tankless but they end up needing multiple heaters to keep up capacity
plumbit
11-17-2013, 12:44 PM
TanklessTankless Tankless thats all I here anymore from my clients as they have been brain washed by green energy. Lets face it "They are NOT green" The cost is high, the maintenance is high, they save very little fuel and on an installation like this one they don't produce enough flow as the restrictors will slow the flow to maintain the water temp. We pull out more tankless heaters as they are never sized properly like this one.The upper floor shower loses pressure as the lower floor uses water. The restrictor reduces flow to maintain temp and the lower floor gets the pressure and the upper starves due to the height gradient. A total load calc of hot water is needed and the heaters need to be at mid flow as they don"t produce volume at full flow. I'm sorry for all of the work of installing a tankless but they end up needing multiple heaters to keep up capacity
I have no love for them either , I have installed a few because of customer demand but I have qualified it with , if and then it needs service , call the manufacturer as I don't service them.
snupytcb
11-17-2013, 01:21 PM
TanklessTankless Tankless thats all I here anymore from my clients as they have been brain washed by green energy. Lets face it "They are NOT green" The cost is high, the maintenance is high, they save very little fuel and on an installation like this one they don't produce enough flow as the restrictors will slow the flow to maintain the water temp. We pull out more tankless heaters as they are never sized properly like this one.The upper floor shower loses pressure as the lower floor uses water. The restrictor reduces flow to maintain temp and the lower floor gets the pressure and the upper starves due to the height gradient. A total load calc of hot water is needed and the heaters need to be at mid flow as they don"t produce volume at full flow. I'm sorry for all of the work of installing a tankless but they end up needing multiple heaters to keep up capacity
tankless water heaters are a great option. and work and save quite a bit of energy if sized and installed correctly. you are blaming the heater for installation error. they are a big step towards being green. being brain washed to conserve energy is not a bad thing. saving energy saves money and a little smaller foot print is nice too. so do you think we should go back to standing pilot, single stage furnaces with on/ off blowers?
snupytcb
11-17-2013, 01:28 PM
I have no love for them either , I have installed a few because of customer demand but I have qualified it with , if and then it needs service , call the manufacturer as I don't service them.
if you don't service them, then why do you put them in? this is how you loose customers and reputation. it just doesn't seem professional. I have a couple guy's who do it that way, but again it's because they don't know enough about them. it just doesn't make sense to me and it is somewhat unfair to the customer. they don't want to have to call a different contractor to fix every different appliance. I guess I am just thinking as if it were me.
GilliganHVAC
11-18-2013, 10:56 AM
If you check the real savings difference there is little savings in energy. The auto dampers and electronic ignition are on instantaneous heaters as well as the high efficiency water heaters. The only difference is stand by heat loss and that is very very low now due to better foam insulations. The cost of multiple instant heaters or one large one with new larger electric services in most cases does not pay off. The gas operated instant heaters are very good but they need more service than a normal high efficiency pulse heater or closed combustion heater. We sell and install both and the Eternal heater has a small storage so that we can use circulators but it still has its drawbacks but at least has some storage to even out the ramp up gas heaters.
eswin65
11-21-2013, 08:44 AM
wait until the 2015 ban on higher capacity electric water heaters comes in....heat pump water heaters and on demand type will be all we can get...and with some of the heat pump types, foot print is a big issue
GilliganHVAC
11-21-2013, 05:34 PM
I wont hold my breath on the high efficiency heaters. They are getting better but with millions out there they wont stop producing tank style. New homes might require them but replacements wont.
Reeking_hvac
12-07-2013, 01:19 PM
wait until the 2015 ban on higher capacity electric water heaters comes in....heat pump water heaters and on demand type will be all we can get...and with some of the heat pump types, foot print is a big issue
This. 2015 all 50 gallon+ atmospheric vent water heaters are no longer able to be produced according to my Bradford rep. Prepare yourselves! People will have the option of going to multiple smaller tanks, downsize to one 40 if the load is small enough, or tankless.
We put eternals in for awhile, don't like Grandhall much. Switched to the new Navien NPE series and love it.
To the OP. How old is the shower valve? I am assuming they are a bit older and have no pressure balance mechanism. If you put in some simple moen positemp shower valves, I believe your problem would be fixed. These will balance the hot pressure with the cold pressure. What size gas line is the heater on, and how long is the run? Is the tankless the first appliance on the line?
Chip Chipperson
12-10-2013, 05:35 PM
undersized cold water line.....newer shower valves have an anti-scald temp control in them.....low cold water pressure will cause a spring to close on the hot water side of the valve...preventing that old "flush the toilet and get burned" problem
Milkhawk
12-12-2013, 09:27 AM
Sounds like hot water lines are undersized
Reeking_hvac
12-12-2013, 08:48 PM
It worked fine on the old tanked water heater, which had constant pressure. Tankless does not have constant pressure. When under high load, it will decrease volume dropping pressure to deliver hot enough water. Without a balancing shower valve, the cold water will overcome the hot water pressure, opposite of what used to happen with toilets. I would start by putting a "green" low consumption shower head on both showers, I'm willing to bet you would get hot water at both showers running together if you do. Or test by running one faucet down stairs and see if you get hot water in upstairs showers. If you do, turn on another, and another, and see of you can replicate it but leave the downstairs shower out of the equation. All IMO, of course!
lentz
01-09-2014, 10:03 AM
We have taked out more tank-less heaters in the last couple months that we have installed. An electric or gas heater with Rec. pump will give you the hot water you need. Just size it right. No one has parts, they just sell them. They corrode up and the price is high. Leave them in he store. They are OK for two people living in the house????
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