I have what may be a plumming question

I have a outside hardy heater with a domestic water heat exchanger. Should the supply from the owb which will be heated any time the unit is in use be connected to the cold/inlet side of the electric water heater?
All I have to go by is one says cold water in and the other hot water out...sometimes the water in will be hot.

The only problem I'm having is what seems like air trapped in the hot water lines that won't bleed out.
It's not a big thing and I can live with it, just wondering if there's a fix.

 

Depending o n type of water heater you are using tube or plate type. Either style will not allow owb water into hot water heater.

 

You can install air purge valve like shown on top.

 

Do you have the manual? Here is the manual for an older model...

http://www.hardyheater.com/Pdf/H2-H4-A.pdf

You aren't supplying the hot water heater from the circulator, are you?

 

When the owb is in use the way it's hooked up there will be heated water entering the inlet side
the only other option is hooking it to the outlet side. I don't have the manual, I'm using what was my dads old
water heater I took out of his house before we had it tore down. I'm not sure what a circulator is but I do have the manual for my old hardy, it's about 30 years old. The way I have it hooked is the same as the way the people who installed it had it on my
propane w/heater I had at the time, I don't remember the hot water sounding like it had air trapped in it intermittently back then.
I went a long time with no water heater when the old gas unit rusted out but I got tired of keeping the old hardy burning all year round just for hot water.

 

The elimination of system air entrainment is a normal function of any steam or hot water heating system . Air purge points must be established at high side of all appliances and prior to the circulating pump to prevent cavitation or water hammer in piping . Thermostatic vents are the most effective , which are open when the system starts up and effectively evacuate system air until operating temps increase and internal thermal bellows elements expand within the air vent and close off the air vent to atmosphere . These air purge units also assist during system freeze proofing in that they allow 14.7 lbs atmospheric pressure to enter the system to properly drain the graded heat exchanger or other heating appliances and associate piping during downtime .

 

Purchased my system about 20+ years ago and installed a tube heater and if I had it to do over would do a plate heater (maybe). Tube heater is just a copper pipe connected to bottom drain to pressure relief valve inlet ran through a larger copper pipe surrounding inner pipe. Inner pipe has domestic hot water running through it and space between out and inner pipe has owb flowing through it to heat inner pipe. On a plate heater, two inner layers separated by alternating plates, owb water flows through one layer, domestic through other layer and heat is transfer through plate contact. Plate heaters (depending on number of plates used) supplies a more endless supply of hot water. Down side to plate heaters is if you have high mineral content in well water, clogs plates and you must build in bypasses and use disconnect fitting that will allow you to clean out mineral with vinegar or chemicals. My well water is high in minerals, so went with tube heater, problem there is heater needs to fill from bottom or sediment will build up and clog lower tube.

 

I fear my old hardy is nearing the end of it's life cycle, about 2 years ago I put a case of evaporated milk in it to stop a leak or leaks in the firebox, it's working so far but it's a shaky repair for sure. I don't know for sure what kind of domestic water heat exchanger is in it but the guy installing it said something about 60 feet of tubing the water ran through before coming into the water heater inside. essentially making it mostly just a holding or storage tank so we'd have warm if not hot water without waiting for it to run the distance from the owb. I read later about circulation pumps but have never had one.

 

You must have 4 lines running into your house, two for furnace heat exchange and two for domestic hot water. The two owb's I have owned have both been Woodmaster 434, 3300. 434 developed a leak and I had 1/4 inch plate rolled for the repair, welder I hired removed bad section and checked for damage in other parts of boiler. I know he repairs many owb's in this area, as well as many brands. When he removed bad section, he thought when it was manufactured outside of inner drum was hit with a plasma cutter, causing a straight etch line, thinning metal, that allowed pin holes to form over time. He repaired it and I was just a worry wart to place it, neighbor wanted to purchase it and was reluctant to sell to him, did not want him to have problems. Neighbor does underground boring for a living and is a pipe welder, did not care about future problems and that was 7 trouble free years ago.

 

You're right, there are 4 lines...I was a little concerned about putting 8 16oz cans of pet milk stop leak in it plugging my heat coil but it seem to be working okay so far...air out the vents warm as ever...I heard the hardys are bad to crack in the weld seams over time but they are all stainless other than the grates, so they won't rust out.

 

The Hardy is kind of different than most boilers. The water jacket that supplies hot water for household heat is open to normal air pressure. Household cold water is run directly into a coil within the water jacket for heat exchange and then directly into the water heater.

 

I was pretty sure I'd hooked it the same way it was...it may be I'm just not using enough hot water to keep it purged as well as before...with the other water heater the wife and kids were here, now it's just me.

 

JW , if you look at the air purge unit that Duce has illustrated you can see by design it allows higher pressure fluid to enter a lower pressure area . When this occurs disolved oxygen and air / non condensibles are allowed to escape out the domed air vent area. This air handler is a simple density based mechanical float trap . Upon start up the float is down and the vent is open , when fluid floods the unit the float raises and seats , closing the vent to atmosphere .

 

That's something I would consider if it can be installed with sharkbite fittings and I can do it but I'm not going to hire a plumber for something that's not that big a deal.

 

The hot water from the heat exchanger should go to the 'in' side of the water heater.

In a pressurized system, air can come from. . .

1. A leak causing depressurization

2. Boiling water

3. A source of air that is a higher pressure than the water.

3 is unlikely since the bladder tank would run out of air pressure

2 is possible, especially if the owb has an internal heat exchanger

Could also be a bad thermostat on the water heater causing over temp. This would also need to include a bad tp valve. I have run into this multiple times, but only on commercial units that are set at 180 anyway.

1 should show up as a loss of pressure at the faucets, except in the case of a bad foot valve.

'Liberals' -- nature's most violent

 

JW , all I am saying is that air entrainment is common . How you rid the air from your heating system which can damage you circulator and cause sluggish performance is up to you . These systems are normally run between 12 to 18 psig , although 30 psig on larger two pipe systems are still common low pressure systems . Also to answer your question the hot water from the heat exchanger should be connected to the inlet line to your elect . water heater !

 

If this is correct,

Then the pressure in the dhw circuit would be roughly 30-50 psi.


'Liberals' -- nature's most violent

 

Yes , because it's a static hydronic pressure of 12-18 lbs along with the combined bladder tank static pressure of similar potential , however the pressure control valve or circulator pressure switch is the determining system pressure factor .

 

I don't have a foot valve, the pump is down in the well.. The hot water could very well be pressurizing the system above the 30psi kick in on the pump but that should show up the same on both the hot and cold instead of just the hot line.
Like I said it's not a real problem just has me curious.

 

Is there a check valve close to the pressure tank?

'Liberals' -- nature's most violent