Thermostatic Mixing Valve On Water Heater

 
Thread Tools Search this Thread Display Modes
Old 03-07-2011, 07:17 PM   #1
New Guy
 
MplsGC's Avatar
 
Trade: General Contractor
Join Date: Feb 2011
Location: Minneapolis, MN
Posts: 28
Rewards Points: 25

Thermostatic Mixing Valve On Water Heater


Hi all,

I am wondering how you feel about installing thermostatic mixing valves on a water heater. I am thinking of what gets used on a boiler for an infloor heat loop. I often see undersized water heaters that get turned up to 140 degrees or more so the homeowner does not run out of hot water. As a parent of two young children this is not something I can recommend. If the water heater is old, no problem, put in one that is the right size. But if it is a 40 gal WH set at 120 deg for a family of four someone will be taking a cold shower.

What about efficiency? Assuming the same demand, is a 40 gal WH set at 160 deg or a 60 gal WH set a 120 more efficient? Thanks for the input.
MplsGC is offline  

Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ContractorTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

   
 

Old 03-07-2011, 07:32 PM   #2
Future Post Deleter...
 
rex's Avatar
 
Trade: Nothing
Join Date: Jul 2007
Location: Nowhere
Posts: 1,734
Rewards Points: 748

Re: Thermostatic Mixing Valve On Water Heater


140+ will kill bacteria...

rex is offline  
Old 03-07-2011, 07:45 PM   #3
LRG WoodCrafting
 
Leo G's Avatar
 
Trade: DIY Home Owner
Join Date: May 2005
Location: Windsor Locks, Connecticut
Posts: 22,333
Rewards Points: 9,158

Re: Thermostatic Mixing Valve On Water Heater


I have a tempering valve on my hot water out. I have the tank set at 160F and the tempering valve set to 125F at the closest faucet. As for efficiency, the higher the tank temperature the lower the efficiency the system will be because of heat loss at the tank. My tanks insulation claims 0.5F/hour loss @ 120F, the higher you go, the more loss you will have.
__________________
Sawdust Follows Me Everywhere

Quote:
Originally Posted by HusqyPro View Post
Carpenter by day.
Mad scientist by night.
http://lrgwood.com
Custom Cabinets in Hartford County Connecticut
Leo G is offline  
Old 03-07-2011, 07:47 PM   #4
New Guy
 
MplsGC's Avatar
 
Trade: General Contractor
Join Date: Feb 2011
Location: Minneapolis, MN
Posts: 28
Rewards Points: 25

Re: Thermostatic Mixing Valve On Water Heater


Quote:
Originally Posted by rex View Post
140+ will kill bacteria...
Good to know. So undersize the WH slightly and install a mixing valve? Although your going to add that bacteria right back in there with the cold water.
MplsGC is offline  
Old 03-07-2011, 07:50 PM   #5
New Guy
 
MplsGC's Avatar
 
Trade: General Contractor
Join Date: Feb 2011
Location: Minneapolis, MN
Posts: 28
Rewards Points: 25

Re: Thermostatic Mixing Valve On Water Heater


Quote:
Originally Posted by Leo G View Post
I have a tempering valve on my hot water out. I have the tank set at 160F and the tempering valve set to 125F at the closest faucet. As for efficiency, the higher the tank temperature the lower the efficiency the system will be because of heat loss at the tank. My tanks insulation claims 0.5F/hour loss @ 120F, the higher you go, the more loss you will have.
That sounds like the situation I am thinking of. Did you install the tempering valve because the WH was undersized?

Your efficiency explanation makes perfect sense. Thanks.
MplsGC is offline  
Old 03-07-2011, 08:12 PM   #6
LRG WoodCrafting
 
Leo G's Avatar
 
Trade: DIY Home Owner
Join Date: May 2005
Location: Windsor Locks, Connecticut
Posts: 22,333
Rewards Points: 9,158

Re: Thermostatic Mixing Valve On Water Heater


No, not really. I like long showers. 41 gallons is my tank size and we have 4 members in my family. On the weekends it gets to be 4 showers in a row without running out.
__________________
Sawdust Follows Me Everywhere

Quote:
Originally Posted by HusqyPro View Post
Carpenter by day.
Mad scientist by night.
http://lrgwood.com
Custom Cabinets in Hartford County Connecticut
Leo G is offline  
The Following User Says Thank You to Leo G For This Useful Post:
flashheatingand (05-03-2011)
Old 03-07-2011, 08:21 PM   #7
Pro
 
BCConstruction's Avatar
 
Trade: Construction
Join Date: Jun 2009
Location: Roanoke, VA
Posts: 12,058
Rewards Points: 4,026

Re: Thermostatic Mixing Valve On Water Heater


Also be careful when turning up older water heaters. the T&P valves wear out and with the combination of incoming pressure and heat you can set the T&P valve off. My wife found this out the other day after turning ours up and flooding our basement out.
__________________
www.bcconstructionllc.com
BCConstruction is online now  
Old 03-07-2011, 09:27 PM   #8
New Guy
 
422 plumber's Avatar
 
Trade: industrial plumber
Join Date: Mar 2010
Posts: 27
Rewards Points: 25

Re: Thermostatic Mixing Valve On Water Heater


I don't know of any code that lets you have hotter water than 115 degrees at a tub or shower. So if you want to cheat and have a high setting on your water heater, you need a ASSE stamped mixing valve, either on the tub/showers, or at the heater. T&P valves don't just wear out, either. They open when they need to, when the temp or pressure is too high. Quite often they don't open because they are calcium carbonated up. If you have high water pressure, high temp, or pressure spikes, install an expansion tank or a PRV.
422 plumber is offline  
Old 03-07-2011, 09:37 PM   #9
The Grand Wazoo
 
KillerToiletSpider's Avatar
 
Trade: It blowed up real good!
Join Date: May 2007
Location: Illinois
Posts: 3,682
Rewards Points: 1,388

Re: Thermostatic Mixing Valve On Water Heater


Quote:
Originally Posted by MplsGC View Post
Hi all,

I am wondering how you feel about installing thermostatic mixing valves on a water heater. I am thinking of what gets used on a boiler for an infloor heat loop. I often see undersized water heaters that get turned up to 140 degrees or more so the homeowner does not run out of hot water. As a parent of two young children this is not something I can recommend. If the water heater is old, no problem, put in one that is the right size. But if it is a 40 gal WH set at 120 deg for a family of four someone will be taking a cold shower.

What about efficiency? Assuming the same demand, is a 40 gal WH set at 160 deg or a 60 gal WH set a 120 more efficient? Thanks for the input.

Increasing temp does not increase capacity, the tank will only hold what it is sized to hold, and the rest is lost to thermal expansion, it doesn't really increase recovery time either, water heats at it's own rate. Most residential water heaters are designed to operate at 120 degrees, and the warranty will say that operating it beyond factory recommendations is cause to void the warranty.
__________________
A flush is better than a full house.
KillerToiletSpider is offline  
Old 03-07-2011, 09:41 PM   #10
LRG WoodCrafting
 
Leo G's Avatar
 
Trade: DIY Home Owner
Join Date: May 2005
Location: Windsor Locks, Connecticut
Posts: 22,333
Rewards Points: 9,158

Re: Thermostatic Mixing Valve On Water Heater


If you have a 40 gallon tank with 160F water in it and you are adding cold water to it through a tempering valve to reduce the temperature to 125F you are increasing the capacity of the system. The tank is still holding 40 gallons of water but it is holding a lot more energy at the same time. When I set my thermostat at 120F I run out of water while taking a long shower. When I have the temperature set at 160F and the temper valve at 125F I can shower until the cows come home.
__________________
Sawdust Follows Me Everywhere

Quote:
Originally Posted by HusqyPro View Post
Carpenter by day.
Mad scientist by night.
http://lrgwood.com
Custom Cabinets in Hartford County Connecticut
Leo G is offline  
Old 03-07-2011, 09:46 PM   #11
The Grand Wazoo
 
KillerToiletSpider's Avatar
 
Trade: It blowed up real good!
Join Date: May 2007
Location: Illinois
Posts: 3,682
Rewards Points: 1,388

Re: Thermostatic Mixing Valve On Water Heater


Quote:
Originally Posted by Leo G View Post
If you have a 40 gallon tank with 160F water in it and you are adding cold water to it through a tempering valve to reduce the temperature to 125F you are increasing the capacity of the system. The tank is still holding 40 gallons of water but it is holding a lot more energy at the same time. When I set my thermostat at 120F I run out of water while taking a long shower. When I have the temperature set at 160F and the temper valve at 125F I can shower until the cows come home.
You also voided the warranty on your tank, and if your tempering valve fails while someone is showering they are going to get third degree burns before they can get out of the shower.
__________________
A flush is better than a full house.
KillerToiletSpider is offline  
Old 03-07-2011, 10:21 PM   #12
LRG WoodCrafting
 
Leo G's Avatar
 
Trade: DIY Home Owner
Join Date: May 2005
Location: Windsor Locks, Connecticut
Posts: 22,333
Rewards Points: 9,158

Re: Thermostatic Mixing Valve On Water Heater


All shower heads come equipped with anti scald valves. Having a catastrophic failure of a bi metal tempering valve is on the extremely unlikely scenario.

My tank had no such warranty limitation on it. It is a side saddle tank operated by my boiler.
__________________
Sawdust Follows Me Everywhere

Quote:
Originally Posted by HusqyPro View Post
Carpenter by day.
Mad scientist by night.
http://lrgwood.com
Custom Cabinets in Hartford County Connecticut
Leo G is offline  
Old 03-07-2011, 11:49 PM   #13
Pro
 
Smatt's Avatar
 
Trade: Plumber
Join Date: Feb 2011
Location: Virginia
Posts: 203
Rewards Points: 150

Re: Thermostatic Mixing Valve On Water Heater


A common misconception is that a 40 gallon h/w heater holds 40 gallons of hot water. This true, depending on were it is in the cycle( after just heating up or getting ready to heat up). There is a rise and fall in the common heating cycle so the temperature you set it at can vary at least 20 degrees if your heater is older it could be more.
Back to the 40 gallons of hot water. If the heater is at the end of the cycle after it has heated up, let us say it is 40 gallons of hot water at 120 degrees. Your heater is at it's max.

When you turn your shower on full hot you may theoretically only get 30 gallons of hot water. Output must equal input, meaning cold water must replace the hot water so therefore it is mixing with the hot. It then is not a true 40 gallons w/h.



In my experience a family of four could not take back to back showers.

I had a 40 gallon gas direct vent w/h and could not take a shower after my 14 year old 90 lb. Soaking wet daughter. That is why I switched to a tankless.
Smatt is offline  
Old 04-28-2011, 11:51 PM   #14
New Guy
 
anon44's Avatar
 
Trade: asdf
Join Date: Apr 2011
Posts: 1
Rewards Points: 10

Re: Thermostatic Mixing Valve On Water Heater


Quote:
Originally Posted by MplsGC View Post
Good to know. So undersize the WH slightly and install a mixing valve? Although your going to add that bacteria right back in there with the cold water.
The bacteria grow in the hot water tank if the temp is set too low. The
cold water isn't sterile, but doesn't grow bacteria since the temp is low
and the water not stagnant.

Same idea as for water coolers that have a Hot dispenser. The cold
water side needs periodic cleaning--not the hot side.
anon44 is offline  
Old 04-29-2011, 08:48 AM   #15
Pro
 
Mike's Plumbing's Avatar
 
Trade: ooo
Join Date: Jul 2010
Posts: 4,967
Rewards Points: 2,000

Re: Thermostatic Mixing Valve On Water Heater


The problem here isn't tempering water, the problem here is you have an undersized water heater. Tempering water doesn't fix this problem, the water heater still has to keep up and recover the loss.

Put in a new water heater designed to handle the demand.

Mike
__________________
see ya!
Mike's Plumbing is offline  
Old 04-29-2011, 09:21 AM   #16
New Guy
 
MplsGC's Avatar
 
Trade: General Contractor
Join Date: Feb 2011
Location: Minneapolis, MN
Posts: 28
Rewards Points: 25

Re: Thermostatic Mixing Valve On Water Heater


An appropriately sized WH makes sense as the best solution for the problem of not enough how water. However if you turn up the temperature on an undersized water heater to 140* you have more stored energy and thus the more 120* water available. The tempering vale seems like a solution to the problem of needing more hot water. Not the best solution but one that cost way less and doesn't throw away a 4 year old WH. Am I missing something? I understand that the undersized WH will not be able to recover the way a properly sized WH would. And when the hot water is gone it does not matter what temperature you have the WH set at.

MplsGC is offline  


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Is it ok to install an expansion tank right on top of water heater? Electric_Light Plumbing 29 10-24-2010 07:22 PM
Water heater - on demand or tanked? G.C. Plumbing 2 09-06-2010 06:49 PM
Sparky needs advice with leaking water heater RJS3rd General Discussion 15 08-05-2010 10:35 PM
please help, have problem with solar hot water heater maleko Plumbing 50 09-05-2009 09:18 PM

Join Now... It's Fast and FREE!

I am a professional contractor
I am a DIY Homeowner
Drywall Talk is for
PROFESSIONAL CONTRACTORS ONLY!

At DrywallTalk.com we cater exlusivly to professional contractors who make their living as a contractor. Knowing that many homeowners and DIYers are looking for a community to call home, we've created www.DIYChatroom.com DIY Chatroom is full of helpful advices and perfect for DIY homeowners.

Redirecing in 10 seconds
No Thanks
terms of service

Already Have an Account?