Tankless hot water to electric hot water question

Problems related to residential installations.

Tankless hot water to electric hot water question

Postby Andy101 » Fri Jan 27, 2012 2:56 pm

I disconnected the tankless hot water system off of my Dunkirk model 3ew1.oot furnace and installed an electric hot water heater for various reasons, one being cost of replacing the coil. So my question is in regards to the aquastat.... I have a Honeywell triple aquastat type L8124a, L8151a... I read somewhere, to keep the furnace from firing when it calls for potable hot water and only fire when heat is needed, that I should diconnect the blue wire and turn the temp setting dials all the way down.
I also read or was told instead of disconnecting the blue wire I should disconnect the red and white and connect them together... All I want to do is keep it from thinking the house needs potable hot water but let it fire when we need heat...

So now I'm not sure which to do.... Id rather not spend more money on a new aquastat and would not hold anyone responsible if they gave me the correct way of going about this even tho it is not the proper way to do it and my house burned down.
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- Tankless hot water to electric hot water question

Postby Freon » Fri Jan 27, 2012 5:30 pm

Do nothing. The aquastat is set so the boiler water temperature is set for heating your house, not domestic hot water. The aquastat may be set higher than your electric hot water heater so your house will heat quickly. There's usually a tempering valve where the tankless hot water exits the boiler and it is mixed with cold water so the domestic hot water is not too hot.

So for now, let sleeping dogs lay.
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- Tankless hot water to electric hot water question

Postby Andy101 » Fri Jan 27, 2012 6:14 pm

Theres also a zone thermostat connected to the aquastat if that matters any.... Really? do nothing? thats the third different replay I have gotten about this situation... Now I'm even more confused....
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- Tankless hot water to electric hot water question

Postby Andy101 » Fri Jan 27, 2012 6:38 pm

Freon -
> Do nothing. The aquastat is set so the boiler water temperature is set for
> heating your house, not domestic hot water. The aquastat may be set higher
> than your electric hot water heater so your house will heat quickly.
> There's usually a tempering valve where the tankless hot water exits the
> boiler and it is mixed with cold water so the domestic hot water is not too
> hot.
>
> So for now, let sleeping dogs lay.


The aquastat is mounted right to the coil. Isnt there a temp sensor off the aquastat that inserts directly into the coil? Its a 2 zone house and one zone is connected to the aquastat which is mounted to the coil
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- Tankless hot water to electric hot water question

Postby Freon » Sat Jan 28, 2012 5:02 pm

Usually, the aquastat has a sensor that is in the boiler water, not the domestic hot water coil. The aquastat would be there whether you had a tankless hot water coil or not. The domestic hot water comes from a separate copper coil heat exchanger that's set inside the boiler, totally immersed in boiler hot water. Since it's a heat exchanger and not a tank like an electric hot water heater, it's called "tankless" hot water.

There are two ways the burner for the boiler will ignite. First, the water in the boiler drops below the aquastat setting. Second, when you call for heat at the thermostat. Again, the aquastat has not direct relationship to the domestic hot water coming from the separate coil inside the boiler. If you check the domestic water connections at the boiler you should see a temper valve. That simply mixes cold water with the much hotter water coming from the coil in the boiler. Now the gallons per minute for the tankless hot water will be dependent on the boiler water temperature... the aquastat setting. The hotter the boiler water (higher aquastat setting) the more allons per minute of domestic hot water you'll have.

The aquastat is set based on the heating demands of the house. For a steam system, the setting may be 160 to 180 since no heat will be forthcoming until the boiler gets to 212. For a baseboard system, the aquastat may be set at 140.

Now the lower you can have the aquastat set and still have comfortable heat, the less burner run time you'll have and that should make for lower energy use.

Can you tell us the other opinions you have heard and what logic they are based on?
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- Tankless hot water to electric hot water question

Postby Freon » Sun Jan 29, 2012 7:45 am

A correction. When I said " There are two ways the burner for the boiler will ignite. First, the water in the boiler drops below the aquastat setting. Second, when you call for heat at the thermostat" I was referring to steam systems. For a normal hot water system, the aquastat is the usual control for the burner and the thermostat controls the circulator pump.
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- Tankless hot water to electric hot water question

Postby Andy101 » Mon Jan 30, 2012 11:17 am

Ok Its a baseboard system and the aquastat is mounted to the the tankless coil so thats why I am thinking they interact. I mean something calls for potable hot water doesn't it?

Here is the post I found about disconnecting the blue wire if the tankless coil has been abandoned;

If a tankless coil is not installed on a boiler where this combination aquastat control is installed, this combination control may still be in use. And that's not always desirable.
In this case, the "LO" has almost no use whatsoever and, if you read the instructions provided by the control manufacturer you'll probably see that the manufacturer calls for the "LO" to be electrically disconnected entirely - it's simply a matter of removing a jumper wire (usually the blue wire pointed-to by our pen, next to the DIFF control.

Now here is the post I got about the red and white wires;

Leave the blue wire in place. Remove the WHITE and the RED wires and connect them together with a wire nut. Removing the blue wire only disables the burner part of the low limit operation. It does nothing with the circulator operation. You want the circulator to run as soon as there is a heat call, along with the burner... The white/red solutions addresses both of those issues.

And that is why I am confused...
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- Tankless hot water to electric hot water question

Postby Freon » Mon Jan 30, 2012 12:30 pm

I need the make/model of both the boiler and tankless unit. I strongly doubt the aquastat probe is sensing anywhere else but the boiler water. It may be very close to the tankless coil but not knowing your specific system, I am speculating.

The simplest system is a burner controlled by an aquastat that senses the boiler water temperature. The tankless manufacturer will specify a minimum boiler water temperature for the correct gallons per minute of hot water. Now your system may be different.
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- Tankless hot water to electric hot water question

Postby Andy101 » Mon Jan 30, 2012 12:47 pm

Ok here we go... its a Dunkirk 3ew1.oot boiler...and a Triangle Tube Phase 3 coil model cbb-e3.7

The L8214a aquastat is connected/mounted right to the tankless coil and one thermostat is wired to it. The other zone is wired to a separate relay
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- Tankless hot water to electric hot water question

Postby Freon » Mon Jan 30, 2012 4:39 pm

Your system is not a true tankless system and therein lies my confusion. You have a stand-alone tank that circulated boiler hot water through a heat exchanger inside the tank to heat the domestic hot water. Now I see why you have possibly 2 aquastats.

I will try and read what I can find about your system but it is something I am unfamiliar with. Any chance the original installer can come back? Someone familiar with this sophisticated equipment would be the best for your questions.
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