Hot water hook up

[muncybob]

The Wood Gun manual shows several options to use the installed DHW coil along with an electric water heater. One option is plumbing the coil in series with the electric tank. To do this does the electric heater always need to be on to avoid scalding hot water? Is it possible the electric water heater would be adversely affected by very high temp water coming form the boiler coil?

Next option shows the coil direct with a tempering valve and it appears 2 shut off valves to allow use of the electric or the coil independently. Finally it shows coil parallel with electric tank and a small circulator between the coil and the electric tank(the circulator can be eliminated if you can thermosyphon?).

I guess my dilemma is what are the pro's and con's to each set up? I plan to run the electric heater only in the summer and will rely on the boiler's coil for DHW the remainder of the year.

 

[muncybob]

Nobody has a boiler DHW coil & an electric water heater(for the summer) with an opinion?

 

[Eric Johnson]

The way I did it when I had a boiler with a coil was to circulate water heater water through the coil when the boiler temp was above 140 degrees. The pump, a cast iron Taco 007, was simply wired through an aquastat sunk into a well in the boiler. Over time, the water in the top of the water heater would match that of the boiler. It didn't hurt anything, though if you plan to run your boiler above the max temp of the water heater's T/P valve, the valve will lift and fill your basement up with scalding hot water. There are several ways around that, including using another aquastat (or even the water heater's thermostat) to shut off the pump when it hits the setpoint.

You will probably want to install a tempering valve somewhere on the water heater's supply line to keep domestic water temps under control.

I know you're not supposed to use a cast iron pump in an oxygenated water situation like that, but I ran mine that way for about 7 years, and it still ran fine when I sold the house. YMMV.

 

[connerfur]

Does anyone see any thoughts on dumping the hot water from the DHW coil into the cold inlet on my existing oil fire hot water heater. I'm thinking about installing it after a ball valve to shut off the cold water supply in and also throwing the ball valve on the PB 150 DHW supply to the house. I'm toying with the idea of leaving the oil tank on this winter as sort of a self regulating storage tank.

 

[Gooserider]

Does anyone see any thoughts on dumping the hot water from the DHW coil into the cold inlet on my existing oil fire hot water heater. I'm thinking about installing it after a ball valve to shut off the cold water supply in and also throwing the ball valve on the PB 150 DHW supply to the house. I'm toying with the idea of leaving the oil tank on this winter as sort of a self regulating storage tank.

You want to keep the DHW and the boiler water from mixing - DHW is oxygenated which is bad for the boiler and heating hardware, boiler water is deoxygenated and probably will taste / smell nasty, and may have contaminants in it that you don't want to be mixing with your precious bodily fluids... The other issue is that domestic water systems normally run much higher pressure than hydronics, so you risk problems putting domestic water into the hydronic system w/o some serious pressure regulation...

If this wasn't what you are planning, don't worry about it, perhaps a sketch of the hookup for what you do want will help us advise you better.

Gooserider

 

[sgschwend]

Can the fresh water loop ever exceed boiling point?

I know the boiler manages the hydronic water temperature to some set point, but the fresh water loop is independent. So what is to keep it from going to steam? Just sizing?

 

[Gooserider]

Can the fresh water loop ever exceed boiling point?

I know the boiler manages the hydronic water temperature to some set point, but the fresh water loop is independent. So what is to keep it from going to steam? Just sizing?

Short answer - not easily....

Long answer...

First off, boiling point is NOT a fixed number - it is a function of pressure as well - the 212*F / 100*C we see in the reference books is at sea level. As pressure drops the boiling point goes down, as it increases it goes up. This is one of the reasons why your boiler system, and your car's coolant system operates under pressure, it gives more of a margin between the operating temperature and the boiling point, or allows a higher operating temperature...

Your domestic water is at a higher pressure than the boiler, so it has a higher boiling point, which makes it harder to boil.

If your domestic loop is heated by water outside the boiler - i.e. a heat exchanger of some sort, the domestic temperature can't exceed the boiler water temperature, just by basic thermodynamics, so the domestic water is indirectly controlled by the same things that control the boiler water temperature.

If your domestic loop is in the water jacket of the boiler, you still have the same deal, as the water jacket is also kept below boiling point for the boiler water.

If the loop is actually in the fire box, (which is normally not done, far as I know) in theory it could get heated to boiling, but if properly designed the boiler controls should have shut the boiler down before it got that hot because the water jacket would have gotten to the shut down point first - but it is really simpler to just put the coil in the water jacket and avoid the possible issue. (IIRC the Wood Gun coil is in the water jacket BTW)

What any of these methods CAN do, and quite often do deliberately is heat the water in the DHW tank to well above the levels that are safe to have coming out of the tap - which is why you will see the constant mentions of needing a mixing or "tempering" valve on the DHW out line - this mixes in cold water as needed to drop the temperature at the faucet to around 120*F which is considered the maximum safe temperature for a hot water tap in order to avoid scalding injuries.

Gooserider

 

[sgschwend]

Makes sense to me,

and mixing valves are easy, I think the 3/4 inch size is about eighty bucks.

As always, thanks for clarifying, the only loop I ever saw was in the fire box, but now that you mention it mine is not there so its temp will be indirectly controlled.

 

[Gooserider]

It is more money, and a bit more plumbing complication, but one of the sweetest mixing valve setups for DHW that I've seen is what NoFossil does on his system - he uses two mixing valves and a heat-exchange coil in his storage tank to give him a near infinite hot water supply... He runs the makeup water to the DHW tank and the first of the two mixing valves through the coil in the main storage tank. If the water coming out of the coil is above a certain minimum, he doesn't even use the water from the DHW tank. If it's below, he uses less of the water from the DHW tank since the feed water is preheated to a warmer temp than it would be if it was just coming straight from the cold water supply. The output of the first mix valve then goes to the second valve which mixes in cold water as needed to give the desired temp at the faucet. However this approach will seriously stretch his DHW supply... As a side note, NF also said that it is worth looking closely at the specs on the mixing valves, he said there is a significant difference between different valves as to how tightly they manage to control the final output temperature. He had one particular valve he said did much better than most of the other ones.

Gooserider

 

[Nofossil]

Here's a link to documentation on my setup. Very high WAF, and doesn't require any extra controls.

 

[Hydronics]

Nofo,
WAF is directly proportional to a Man's peace!
I appreciate your knowledge but most of all your humor! checked out your website, I like the disclaimer....

 

[wantstoburnwood]

I have an electric water heater installed with a circulator in line with my boiler coil. I don't have controls hooked up yet to turn the circ. on and off but I used it last spring by just plugging it into a 110 v outlet. The hot water from the cooil is into the top of the heater so hot water is always available. There is a link here for a diagram to hook it up. pm me your email and I will forward it to you.

 

[brad068]

Guys, I got a setup that may seem awkward but works. I installed a plate heater, plumbed potable first into plate then out of plate into a mixing valve on discharge of water heater. I got the mixing valve set so hot water is going directly through plate and into the plumbing tempered with cold water coming out of the water heater. The cold feed is split before plate to feed plate and water heater. My water heater is electric and is off the whole time I am heating with wood. The plate exchanges enough heat that it is like an on-demand water heater. When I stop using the plate, I rotate the mixing valve all the way the other way, turn on the water heater and use electric then. Long story short is that I have the two feed ports on the mixing valve working with hot and cold in both. The valve has worked fine so far. I get some weird ideas sometimes. One good think is that I don't have any standby losses from the water heater sitting idle. And If I do need electric backup it only takes a few minutes to get the water heater up to temp.