Domestic hot water...

[lapeer20m]

I am getting ready to make the heat exchanger to heat my dhw with the owb. My plan was to make a sidearm with 1" outside and 3/4" inside. Then I had a brilliant idea!

Wouldn't it be more efficient to run 1/2" soft copper inside the water heater? It could enter the drain through a copper tee and exit out the top where the pressure relief is located. I googled it and it appears that nobody does this....

 

[colson04]

hmm...very inventive idea.

Wouldn't there be quite a pressure drop pumping your OWB water through 1/2" line from 1" though?

 

[NSMaple1]

Sounds like you're talking about a home-made tankless coil type of thing?

It should give you hot water OK, as long as you can get the joints all water tight.

 

[mtfallsmikey]

BW, State, A.O. Smith make HWH's w/ internal coils, for solar.

 

[cantoo]

Side arms are proven to work. Coils inside a hot water tank maybe not so much. Lots of Mother Earth type sites have pictures and explanations of coils in tanks of water setups, I've read quite a few of them and decided I don't need no water borne bugs growing so I used a plate heater for one house and a sidearm on the other, they both work well. PS, soft copper isn't very cheap either. If you are making one I would use at least 2" copper for the owb water and 3/4 on the domestic.

 

[NSMaple1]

How do coils grow bugs?

 

[mtfallsmikey]

How do you put a copper coil inside of a water heater? Cut a hole? they are glass-lined.

 

[NSMaple1]

I think getting enerything water tight would be a bigger issue - getting the pipe in would just take a lot of patience & good fishing.

 

[cantoo]

NSMaple1, there are many different types of water coils some are open tank ones and they can breed bugs if the temperature is right. If it's a sealed system you are usually ok but you need to make sure temps stay high enough.

 

[OH_Varmntr]

Build a side-arm or install a flat-plate HX (can be had for ~$100). Good luck fishing a coil of copper through a hot water tank.

Also, how much can you get a coil of 1/2" copper for? Have you figured out how much you're going to need?

 

[mtfallsmikey]

NSMaple1, there are many different types of water coils some are open tank ones and they can breed bugs if the temperature is right. If it's a sealed system you are usually ok but you need to make sure temps stay high enough.

What bugs? Are you using any type of water treatment in your boiler, or a biocide? Then your worries are over.

 

[skindaddy]

30 plate heat exhanger not bad priced prob works alot better, far less time consuming, small compact, and will put out hotter water then you can stand for as long as there is a fire going.

 

[upsnake]

I put a 10 plate hx in, and it keeps everything up in the 130-140 range as long as long as there is a fire, and the nice thing was the hx was like 35-40 bucks.

 

[lapeer20m]

Thanks for all of the advice. I ended up installing a sidearm and am impressed with how well it works. I also installed a tempering valve to keep the water at a safe temperature.

What I had planned on doing was installing just a single piece of soft copper maybe 6 feet long. I was going to install it through the bottom drain and out the pressure relief, soldering it through a tee kind of like the sidearm so the drain and pressure relief could be reinstalled.

 

[NSMaple1]

NSMaple1, there are many different types of water coils some are open tank ones and they can breed bugs if the temperature is right. If it's a sealed system you are usually ok but you need to make sure temps stay high enough.

I have never heard of this happening. Have any examples you can link?

The only thing I have heard of as a possibility is Legionaires in DHW heaters that are set too low. And that is pretty remote. I think any kind of boiler system see temps high enough to not have to worry about bugs.

 

[cantoo]

This is the type of system I was talking about. There was another one using a wooden box in a crawlspace with a tarp to keep the water in that was even more primitive but I can't find it anymore. It was also solar heated. The problem is that on cloudy days the domestic water doesn't get hot enough and can become a breeding ground. At least that's what I read when I was looking for methods to heat my water in the summer.
Heres a quote. I was surprised that 90 to 108 is the ideal growth temp.
According to the paper "Legionella and the prevention of legionellosis,"[18] found at the World Health Organization website, temperature affects the survival of Legionella as follows:

• Above 70 °C (158 °F) - Legionella dies almost instantly
• At 60 °C (140 °F) - 90% die in 2 minutes (Decimal reduction time (D) = 2)
• At 50 °C (122 °F) - 90% die in 80–124 minutes, depending on strain (Decimal reduction time (D) = 80-124)
• 48 to 50 °C (118 to 122 °F) - Can survive but do not multiply
• 32 to 42 °C (90 to 108 °F) - Ideal growth range
• 25 to 45 °C (77 to 113 °F) - Growth range
• Below 20 °C (68 °F) - Can survive but are dormant, even below freezing

Lapeer wasn't planning on this type of open tank anyway. He was installing it inside of a sealed tank.

 

[OH_Varmntr]

My dhw is the first hx in my loop. Hot water in the tank is around 160-170 I haven't measured it directly yet. Honeywell Thermostatic Mixing valve keeps it down to safe temps at the fixtures.

I have had the dishwasher and 2 showers all going and still haven't lost any hot water. I'm running a small brazed plate hx, either 8 or 10 plate I don't remember.

 

[mtfallsmikey]

Ok, so he cut the top out of steel tank and put the coil in, not an electric/gas hot water heater, which is glass lined. The water temperature will depend on how fast you are flowing water thru the copper coil, which is that dude's case is no more than an edumacated guess...