dhw

[maplewoodshelby]

Does anyone that uses a built in dhw coil in their boiler pipe the incoming water supply directly to the coil and simply use the home water pressure to move the water throughout the house? My buddy does this with his OWB and he has it run to the existing water heater where his hot water plumbing to the house begins. He does not run the heated water into the tank but just hooks on the hot water out line and has a valve between his hookup and the water heater to prevent water from going into tank. He claims his coil is only 3 ft long and about 4 inches which is about the same as mine and he never runs out of hot water. The only drawback is that he must wait about 1 minute for the hot water to make it to his faucets? Anybody else do this and whats your thoughts versus using pump and temp controller

 

[maplewoodshelby]

Since I will apparently be the second person on the planet to do this I will report back how it works

 

[Gooserider]

I would think the downsides of doing that way would be that it will only work when the boiler is hot, and some level of unpredictability about the hot water temps - depending on what stage the fire is in, how much water is being drawn, etc... Unless he's using a tempering valve that you didn't mention, I would not consider it to be a safe install because of the scalding risk, plus wasting the cold water in the lines each time you need to run water.

IMHO it is far better to use a circ to overcharge the hot water heater, and draw from that, possibly using a NoFo style double tempering valve setup, and pulling the make up water through the boiler loop as well. More efficient, less water consumption, and safer as you'd have a predictable water temp at the tap.

Gooserider

 

[maplewoodshelby]

Do you have a link to the nofossil setup? I've searched and cant find it. I agree that the circulating pump method is preferred and will probably go that route. My dilemma is that I have two electric water heaters. one is 60 gallon and one is 20 gallon (runs sink and dishwasher in kitchen). they are at opposite ends of the house. My first thought was to just hookup the big heater with temp controller, run pex with circulator into my coil and call it good. Leave the small tank on electric However, I am a perfectionist type and would like to have them both hooked up somehow but not sure how to work it without running the circulator continously thru both of them because they have different water volumes and will be calling for heat differently. The 20 gallon tank will cycle much more than the larger tank so my thoughts are to put my temp controller on the smaller tank and have both tanks hooked to the same pex lines. This will kick circulator on more but I guess wont hurt anything.

 

[twitch]

Gooserider,
When you say overcharge the hot water heater, by how much. Will they withstand 170-180 F water? I know a tempering valve would be needed on the output but what would the max safe temp be for these? I haven't set my boiler up yet to do DHW as my electric water heater is only 3 years old, and didn't know if it would be worth the time / expense.

 

[maplewoodshelby]

While there is some conversation on this subject I have a couple other things.
I havent read up on it much yet bu tI do know that electric water heaters have a switch of some sort for overheat protection that has to be reset if it overheats. I'm assuming this switch only works when there is power to the water heater which mine will not have.
Also, what about dishwasher incoming water temps? Can they be damaged with hot water? I will be installing tempering valves before the water gets there but just wandering what the limit is on most dishwashers (without reading my owners manual)

 

[Gooserider]

couchburner :

Do you have a link to the nofossil setup? I’ve searched and cant find it. I agree that the circulating pump method is preferred and will probably go that route. My dilemma is that I have two electric water heaters. one is 60 gallon and one is 20 gallon (runs sink and dishwasher in kitchen). they are at opposite ends of the house. My first thought was to just hookup the big heater with temp controller, run pex with circulator into my coil and call it good. Leave the small tank on electric However, I am a perfectionist type and would like to have them both hooked up somehow but not sure how to work it without running the circulator continously thru both of them because they have different water volumes and will be calling for heat differently. The 20 gallon tank will cycle much more than the larger tank so my thoughts are to put my temp controller on the smaller tank and have both tanks hooked to the same pex lines. This will kick circulator on more but I guess wont hurt anything.

I believe NoFossil describes his setup on his website, which is linked in his signatures on his posts... Essentially he uses two mixing valves in series - His makeup water is run through the coil in his storage tank, the first valve mixes water from the DHW tank and storage heated makeup, the second mixes the output from the first valve w/ cold water. Because the first stage mix minimizes the amount of water pulled from the DHW tank, he gets maximum use from it. Not sure if I would get that fancy in your case as it would take a bunch of extra plumbing and four mixing valves... We had some discussion a while back on a dual hot water tank setup that sounds a lot like what you are describing, and I think your idea was pretty much what we came up with on how to do it, except that I think they put an aquastat on both DHW tanks wired in parallel so that either tank could kick the DHW loop circ - the reasoning was that the tanks would see their loads hitting at different times of day (Big tank during morning showers, little tank during evening cooking and dishwashing) so it was best if they could each call as needed...


twitch:

Gooserider,
When you say overcharge the hot water heater, by how much. Will they withstand 170-180 F water?

From what I've seen, bring them all the way up to the maximum the boiler puts out... The tanks should be able to handle the hot water, though you might have to change out the T&P valve for one with a higher temp rating or just a pressure relief function. Also see the note below on possible element protection devices.

I know a tempering valve would be needed on the output but what would the max safe temp be for these?

Code says 120°F maximum at the faucet, and unless you were getting complaints I'd think 110-115°F would be safer.

I haven’t set my boiler up yet to do DHW as my electric water heater is only 3 years old, and didn’t know if it would be worth the time / expense.

Your call on the money, but it isn't terribly difficult to tie an electric heater into the boiler system using a "sidearm" type HX set up as a zone, and that would get rid of the electric heating bill, at least during the heating season...

couchburner:

While there is some conversation on this subject I have a couple other things. I havent read up on it much yet bu tI do know that electric water heaters have a switch of some sort for overheat protection that has to be reset if it overheats. I’m assuming this switch only works when there is power to the water heater which mine will not have.

Some heaters do, and while it shuts off the elements, it doesn't do any other harm... My understanding is that if you do have a heater with this function, the switch will trip whether there is power going to the heater or not, as it's a thermal trigger. If so, and you never use the electric, it's obviously no big deal. If you do a seasonal change over, again it isn't a big problem, you just have to remember to hit the reset at the same time you turn on the heater power. The only case it's an issue is if you are automatically switching back and forth during the heating system, in which case there are ways to bypass the switch.

Also, what about dishwasher incoming water temps? Can they be damaged with hot water? I will be installing tempering valves before the water gets there but just wandering what the limit is on most dishwashers (without reading my owners manual)

Dishwashers can definitely take anything coming out of the tempering valve (120°F max) and most can take considerably more - again up to the 180°F or so max you will get from the boiler, and the hotter their water, the more effective they are at cleaning and sanitizing your dishes... I have heard of some folks that run a separate dedicated dishwasher only line that they pull off before the tempering valve in order to get the hottest possible water into the dishwasher.... This can be an energy saver as many dishwashers will otherwise use an electric element to heat their water to a higher temperature than they normally get from the hot water tank. (Commercial dishwashers are actually REQUIRED to run at near boiling temps for sanitary reasons.)

Gooserider

 

[maplewoodshelby]

Gooserider,
You are the man! Thanks for taking the time to talk on this. I will keep you posted on how my setup works out

 

[twitch]

Gooserider,
Thanks for the info, looks like I have a project for this spring / summer.

 

[sorethumbs]

I have heard of some folks that run a separate dedicated dishwasher only line that they pull off before the tempering valve in order to get the hottest possible water into the dishwasher.... Gooserider

You can also tee off that line to a dedicated instant hot water tap at the kitchen sink. Instant hot chocolate, tea, soup, Tom & Jerry's, baby bottle warmer, meat defroster, and whatever else you can think of that you heat water for.

 

[Gooserider]

I have heard of some folks that run a separate dedicated dishwasher only line that they pull off before the tempering valve in order to get the hottest possible water into the dishwasher.... Gooserider

You can also tee off that line to a dedicated instant hot water tap at the kitchen sink. Instant hot chocolate, tea, soup, Tom & Jerry's, baby bottle warmer, meat defroster, and whatever else you can think of that you heat water for.

True, and I've seen setups that do that, but I must admit that I'm nervous about anything that potentially allows a person to come in contact w/ scalding temperature tap water, however that might just be me...

Gooserider