DHW Tank Setting for Summer

[bpirger]

Hi All:

Been burning the Garn since Nov. 2010, not a drop of oil. Great! I have been burning spruce all this summer to heat my DHW. I took another step at better insulating the Garn and can readily get 3 days from a burn (up to 190). Great!

What do folks set their DHW tank to during the summer? I dropped mine down to 110 and I think I can go 4 days if I desire. Don't need to hottest water for the summer for shower, dishwasher heats the water a bit, and haven't noticed a problem with the laundry. I have heard of issues with the indirect DHW being set low, with critters in the water, but I don't know if this is a real concern or not. Haven't had any problems here...

Any comments? Won't be long until the snow flies....actually looking forward to the end of this heat, but I always am.

 

[nate379]

My hot water is set to 140*. Any colder than that and I have to run near full hot to get warm water and the washing machine "warm" is cold. My cold water is about 40* though.

 

[Clarkbug]

I would be a little worried about keeping your domestic at 110, only because thats a great temperature to grow all sorts of nasties in there. For commercial systems, they typically store at 140 and temper down to 125, and I keep my personal tank here at 125.

Its probably a non-issue, depending on how much hot water circulates through your tank in a day, but you should just know that its a great incubator if you get something nasty growing in there. Legionella is the one that is always thrown out, but it isnt typically an issue unless you have someone with a compromised immune system in your house.

 

[bpirger]

Agreed. Given that we typically run through estimating 200-250 gallons of hot water a day, and the tank is a 53 gallon indirect, I'd think the turnover would be such that it would not support the happy life of critters. Now, they can likely be attached to the sides of the tank....on top of whatever slidge is there, and I perhaps only the heat will kill them.

I typically keep the tank at 120, have for years, and have never found an issue with water supply or supplied temp. My controller will heat the tank up to 123 and then shut off....after a few minutes of purge (additional running of the DHW pump without firing the boiler (or in this case brining in hot water from the Garn)). I have seen the system run "forever" with boiler supply at 124 and DHW at 123....until the boiler supply drops....then the DHW will start to drop of course. So going down to 110 really brings in another effective day for this summer time burning. Losses really drop off when the Garn is in the 120 range. Heck, last week I think the Garn was gaining heat from the air! It's just really nice extending out the burn times.

Perhaps an occasional boosting of the DHW up to 140 to eradicate the biologic that may be present would satisfy my greater concern....though have to make sure no one gets scalded on those few days.....

 

[heat seeker]

You could put a mixing valve in the hot water line, then the temp at the faucets could never exceed the temperature that you set. I did that because the DHW was just too hot for safety at the faucets.

 

[Don2222]

Hello

I set my DHW tank to 130 degrees. Any lower and my wife complains! I could get by with 120 Degrees fine!

To keep a good eye on it, I installed a temperature guage. See pic below!!

Although I turn it up a bit in the winter to use the Ice Melt tap for the driveway and steps.

See pics here
https://www.hearth.com/econtent/index.php/forums/viewthread/71142/

 

[in hot water]

Two issues, one being the growth of bacteria. For that most experts suggest the tank be run to 140F or more for at least 1 hour per day. That temperature has become a requirement in some areas.

But that is much too hot to send out to the faucets and showers. The best solution is to add a quality thermostatic mixing valve at the tank. 115- 120F seems to be the temperature most agree on. In some cases plumbers will run a separate high temperature hot to the dishwasher and maybe wash machine. Soaps work best with hot water.

The thermostatic mixing valve you choose should have the proper listing to assure code compliance. An ASSE 1017 goes at the water heater as a point of distribution valve. A 1070 would be a point of use valve at the sink or shower. A 1070 valve cannot be adjusted above 120F, by design. Most shower valves are available with some sort of scald protection either temperature, pressure or both.

Thermostatic mixing valves are a must on solar water heaters and indirect tanks that have the potential to reach high temperatures either through over heat protection functions, or improper piping from misplaced or omitted check valves, etc. Scalding can and does lead to deaths too frequently especially with infants and the elderly.

Remember mixing valves will require some cleaning and maintenance depending on how hard your water is and how much flows through it. Install them with isolating valves so you can remove the cartridge and soak it in vinegar or de-limer from time to time.

hr

 

[bpirger]

Does anyone reading this have a mixing valve on the output of their DHW? I've probably only seen 20 DHW tanks in my lifetime, but I've never seen a mixing valve on the output. It seems like the mixing valve makers of the world dream to me.... I've never set my tank over 120, in the past 8 years since I built the house, and have never had a problem. I'm overweight, maybe I'm eating high calorie bacteria in my hot water!

I love burning once every 4 days for DHW! And bringing the tank up to 140 is no problem every now and then. I wonder if it is filled with crud packed all on the sides from critter growth. Heats as fast as ever, so I think not. Never before have I felt "you have to be kidding me", but I must admit, I really do here!

Mixing Valve Association and the fossil fuel people....heat to 140. OK, I'll stop now.....geez!

How about with city water packed fill with chlorine? Do they say the same thing?

 

[heat seeker]

I have a mixing valve on the output. Otherwise, the hot water at the faucets was too hot for safety, and I'd get wide temperature swings as the furnace switched on and off during a shower. It helps hold the output temperature more constant, which I really like.

 

[Frozen Canuck]

Does anyone reading this have a mixing valve on the output of their DHW? I've probably only seen 20 DHW tanks in my lifetime, but I've never seen a mixing valve on the output. It seems like the mixing valve makers of the world dream to me.... I've never set my tank over 120, in the past 8 years since I built the house, and have never had a problem. I'm overweight, maybe I'm eating high calorie bacteria in my hot water!

I love burning once every 4 days for DHW! And bringing the tank up to 140 is no problem every now and then. I wonder if it is filled with crud packed all on the sides from critter growth. Heats as fast as ever, so I think not. Never before have I felt "you have to be kidding me", but I must admit, I really do here!

Mixing Valve Association and the fossil fuel people....heat to 140. OK, I'll stop now.....geez!

How about with city water packed fill with chlorine? Do they say the same thing?

Not sure how to make this clearer/more understandable: Hr's post above yours was spot on, he did state the various requirements by code & other governing authorities. He outlined the dangers of running too hot or cold. He outlined how some types of systems have the potential to over run the settings such as an indirect or solar system. Mixing valves are a simple solution to the problem of 140 water being too hot. BTW 140 is also required install temp setting here as well due to risk of bacterial growth below that temp. No; no one is kidding you, industry is mandated to install at 140, 140 can & does scald users so a solution was needed = mixing valve. Allows system to be hot enough to kill bacteria while at the same time being safe for users. I promise, no kidding that is how the system is supposed to work when it is done right. Eliminate bacteria with high temp while being safe for users. Done wrong it does only one or neither.

If as you say you have run your tank at no more than 120 over the past 8 years; great, your fortunate to have no bacterial growth. Don't count on your good fortune continuing.
If you love burning once every 4 days for DHW, why not turn up the tank to 140 or higher & burn once every 6-8 days. You get the peace of mind knowing that's too hot for the bacteria as well as the extra days rest = win win. Right? BTW municipalities use chlorine to kill bacteria & other nasty things present in the water they draw from, it has little to no effect on the bacteria that can grow in hot water because that water has not been heated yet. Every municipality asks you to follow local code so yes, they would say heat water to 140.

 

[jebatty]

...we typically run through estimating 200-250 gallons of hot water a day....

The low-flow faucets and showers, cold water clothes washing, and shared bath water has really paid off, as our usage is less than 90 gal/day, the capacity of our electric hot water heaters. That included a recent week with guests when 14 family members stayed with us. Easily explains our less than $5/month electric hot water heating bill, which is off-peak and electric for hot water only late at night. Would never make any sense to burn wood to heat dhw. But wood we burn 24/7 during the heating season for the house and shop. Have cut our annual heating bill to less than $200, which covers electric backup for those winter excursions.

 

[jebatty]

It is pretty well known in general that copper ions inhibit bacterial growth, so much so that many hospitals now are putting copper in hospital rooms. There are conflicting reports on this, but it well may be that copper plumbing for dhw provides a level of protection against all nasties that may inhabit a dhw system. Fortunately, we never have had an issue here, and we do not heat to 140F, but do have all copper hot/cold plumbing.

 

[bpirger]

Jim....when you say "shared bath water", that makes me think you aren't worried about bacteria! I hope you take that with all the love that is behind it....I couldn't resist!

Not at all interested in starting anything here....I've never seen a mixing valve on DHW. I fully understand why it could be used to assure safety. Find it hard to believe it is standard installation today. Fully believe code may specify it should be.

Increasing tank temp would decrease time between burns....and also increase the minimum water temperature usable from storage. Heating to 140 would require at least 141 degree water devliered to the DHW tank, and practically speaking, considerably higher. With a all radiant heat load typically happy with less than 120....it would be a shame not to access those other 200,000 BTU in the Garn. But, as has been discussed previously in other threads, using a instanteous electric water heater to boost the DHW to whatever minimum one desires, so that the storage can be used down to the radiant requirements, might be the best overall system design.

 

[skfire]

Mixed down DHW is fast becoming code in most states and a std in NYC, NY state may be as well, I will check and let you know for sure.
I did not have it in my old set up either and had my tank set to 125..got lucky for 9 years so I am not pushing it, my new set up has a mix down( though I have mixing vlvs on all my faucets...no need wasting). Legionaaire;s disease...not good
https://secure.wikimedia.org/wikipedia/en/wiki/Legionellosis
70 to 80 °C (158 to 176 °F): Disinfection range
At 66 °C (151 °F): Legionellae die within 2 minutes
At 60 °C (140 °F): They die within 32 minutes
At 55 °C (131 °F): They die within 5 to 6 hours
Above 50 °C (122 °F): They can survive but do not multiply
35 to 46 °C (95 to 115 °F): Ideal growth range
20 to 50 °C (68 to 122 °F): Growth range
Below 20 °C (68 °F): They can survive but are dormant

Scott

 

[bpirger]

Here's an interesting link....

http://www.treehugger.com/files/2009/03/turning-down-water-heater-safe.php


Certainly not the first time this conversation has been held. Certainly sounds like the working theory is very different in Canada than the US, though the US is apparently starting to adopt the higher temp. Certainly can understand the strength of your conviction Frozen.

Interesting at the end it isn't from drinking the bacteria....you have to get it in your lungs. It is a pnuemonia related strain afterall. Perhaps that is why the lower temp users don't die quickly. If 25% of tanks in Canada are believed to be infested, and that's with the 140 setting, then it must be MUCH higher with a low temp tank. Though I must admit I have to really question how 25% can be infected at 140, or question the table of death vs. temperature of the critter.

 

[peakbagger]

My solar hot water is plumbed into the same circuit as my Aquatrol hot water maker, they both run through the same Honeywell mixing valve, it has a 140 F high temp protection built in. The solar is unregulated so it can get up to 160F. I heat the hot water maker with my wood boiler and its also set for 160. I also have a expansion tank on the circuit which many people dont have. Prior to installing the tank, my hot water faucets would drip on occasion when the system was heating up, once the tank went in the dripping stopped.

 

[bpirger]

I wondered what would happen with the expansion of the water in the DHW tank. Seems like it would push against the bladder in the well pressure tank, less actual water in there to develop the system pressure.

 

[nate379]

Suppose with little kids it could be a problem, but otherwise no problem here with the water being at 140* at the tap. Takes a bit to get warm, so it's not like turn wrong faucet on for some reason and liquid hot magma is pouring out.

 

[Frozen Canuck]

I have apologise for my previous post bpirger. Thats what you get when you spend way too many hours working in the sun & post before bed = absolute garbage. Sorry for that.
The points in the post & thread are valid, I did a horrible job of stating that.
What we will typically see here is serious outbreaks in seniors complexes, people who already have a compromised immune system.
When the bacteria becomes established it races through that population with devastating results.
Don't get me wrong many homeowners choose to run at lower temps to save money & never have a problem, however when it goes bad it does so in a rapidly with sometimes devastating results.
A trip to the hospital is one thing, a trip to the cemetary is another altogether.
FWIW I turned up my tank temp after the outbreak that gave the bacteria it's name in your country in the 70's.
I view it as cheap insurance & the mixing valve is the same against scalds.

 

[bpirger]

No need to apologize...nothing was ever wrong. I understand what it is to be passionate about something....just get me going on many different topics. And indeed, does seem to hit those most susceptible. I think I'll start cranking my tank up every now and then for an overnight sitting period or something at 150, right after a burn say, and hopefully whatever buggers are there will be greatly reduced.

I think it is indeed critical that people be aware of the possibility. I know when looking at some of the save energy mantras, lowering the tank is often stated, but I don't always see the potential problems discussed. They always should be....and let the user decide/beware.