Aquastat settings with indirect water heater

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Old 12-10-07, 07:00 PM
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Aquastat settings with indirect water heater

Hey Guys,

I've done a bunch of reading but don't believe I've figured out what I should do. I have a forced hot water boiler that used to supply domestic hot water via the tankless coil. About a year ago, I had an indirect water heater installed as a zone and they disconnected the tankless (it's still inside though).

Within the last few days, two additional zones have been added to the system original system (2 heat zones and the newer zone for hot water), totaling 5 zones (with the hot water heater). One of the additional zones was breaking the master suite onto it's own zone from the rest of the first floor, and the other was the addition of a bonus room being finished over the garage.

The boiler had the original 2 zone control, plus a newer single Taco control for the water heater, installed about 8 months ago. Wiring was a mess. So with the new zones being added, I opted for a new Taco 6 zone zone control box with priority (one of the zones is unused). The electrician pulled the wiring mess off and redid everything, and it looks great.

Long story to get to a quick question - since the tankless isn't used, he set the Taco control box up as "cold start" which seems to make sense. But he wasn't sure about what setting the Aquastat should have or if it was even set correctly after the water heater was installed.

I had always thought one of the advantages of the indirect water heater is that the boiler would only run if a zone called for it, and not just to maintain temp. I guess once you have an aquastat you always do, so I'm not sure what to do. Right now, the high is at 180, and the low is around 140. I read articles about condensation, but I'm still not sure if I'm ok, if I should lower it, etc.

Any advice?

Thanks a bunch.
 
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Old 12-10-07, 07:52 PM
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I wouldn't mess with the low, but unless its super cold outside you could lower the high setting if you wanted to and save some fuel.
 
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Old 12-10-07, 08:00 PM
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Steven, the aquastat is the thing that's keeping the boiler warm, the control panel has no say over that.

Leave the HIGH at 180*, cuz that's the temp for the water when you have a heat call. You need hot water for that.

The LOW and the DIFF control the 'keep warm' function.

You could change the aquastat to a cold start model.

A while back a poster gave some instructions for removing a wire on a triple a'stat to convert to cold start.

You could turn the LOW and DIFF down to minimum settings and live with the extra oil burning... but about condensation: since there isn't any water circulating when the boiler is firing to stay warm, you don't have to concern yourself with the return temps. But if the lowest setting is 120*, well, you might... I think the condensing point for oil is like 115* and for gas is 135*...

Also, you need to be aware that sometimes happens that boilers start to leak a bit when they are converted to cold start because the metal shrinks as it gets cold.

What brand of boiler ? are you firing Gas or Oil ?
 
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Old 12-10-07, 08:17 PM
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Thanks guys. By the way, the diff is set to 20.

I need to correct something too. I thought the electrician wired the taco control box as cold start, but I see now that he didn't, he wired it as a tankless. He must have switched it without me knowing he had to. Makes sense really, as there is an aquastat.

He did mention that the lower setting could be lowered. I think he said it was at 160, so he put it to 140. So do settings of 180 high, 140 low, with a diff of 20 make sense considering I'm not using the tankless anymore?

I'm burning oil, and the brand of the boiler is Trianco. I'm told it's not a great one, but in the famous words of the oil company, "It's the best one I have." It's about 11 years old.

My concern over cold start vs not is really around oil savings. It just sounds like it will run less, which you would think would use less oil. Maybe not. I'm told the nozzle in my boiler is something like .75 gallons/hr or something like that.
 
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Old 12-10-07, 08:43 PM
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Steven, the Taco box doesn't have anything to do with cold start / tankless . All that does is operate the valves, and fire the boiler when any one calls for heat.

The cold start thing is strictly in the aquastat.

I think cutting the diff back to 15 or even 10 might save a little more oil, but if you notice very short cycles on the burner, try bumping it up a bit.

Going to cold start would save quite a bit. Problem is as I said, the boiler may start to leak...
 
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Old 12-12-07, 11:44 AM
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Thanks. So why do you have to configure the control box for one or the other (cold start or tankless) via the jumper?
 
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Old 12-12-07, 12:10 PM
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I would make it cold start and if the gasket leaks replace it and that problem goes away. This is a steel boiler so there are no push nipples or gaskets between sections. The best way to make it a cold start boiler is to change the aquastat to a high limit only, and have the electrician change to cold start wiring on the Taco control. If you don't want to do that set the aquastat as low as it goes and set the differential to 20f so the boiler does not short cycle. Honeywell does not like you disconnecting the blue wire to make this a cold start control.
The Taco control will not use the ZR and ZC terminals in your aquastat if wired as cold start. The jumper will remain in.
 
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Old 12-12-07, 03:09 PM
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Originally Posted by StevenG View Post
Thanks. So why do you have to configure the control box for one or the other (cold start or tankless) via the jumper?
Good question ! Which control box are you using ? I'd like to take a look-see myself.
 
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Old 12-18-07, 04:00 PM
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if you stayed with the low and high aqustat you can hook up an hour meeter and see witch settings run less or more and what is comfortable for you!
your 6 switch taco box ha s a prioority zone witch you can hook up your aqustat for the water heater. so your indirect water heater would be your priority zone.
 
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Old 12-18-07, 04:36 PM
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Originally Posted by rbeck View Post
Honeywell does not like you disconnecting the blue wire to make this a cold start control.
.
And I'm 99% certain that the UL listing on the control would be 'compromised' ...
 
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Old 12-19-07, 08:48 AM
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Originally Posted by NJ Trooper View Post
Good question ! Which control box are you using ? I'd like to take a look-see myself.
Taco SR506. Zone 6 is the indirect water heater set as a priority zone. Zone 5 is empty.

I don't get what Tony said though "your 6 switch taco box ha s a prioority zone witch you can hook up your aqustat for the water heater."
 
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Old 12-19-07, 04:39 PM
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I think Tony was saying what you just said... zone 6 on that control can be switched for a normal zone, or priority, as you have it, meaning that when the water heater is calling for heat, the other zones get none, until the water heater is done ...
 
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Old 12-19-07, 04:51 PM
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Steven, I understand now what you were saying about cold start / tankless... that jumper change causes the circulators to behave properly in a tankless situation.

The point I was getting at though, is that changing that jumper is not going to stop the boiler from staying warm, the aquastat still controls that.

That jumper simply allows the 506 panel to control the circulators in the same fashion as the aquastat would if the circ were still connected to it.

In other words, you can't convert to cold start at the Taco panel, you still would need to change the aquastat, or hack up your existing aquastat...
 
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Old 12-20-07, 08:48 AM
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Originally Posted by NJ Trooper View Post

That jumper simply allows the 506 panel to control the circulators in the same fashion as the aquastat would if the circ were still connected to it.

In other words, you can't convert to cold start at the Taco panel, you still would need to change the aquastat, or hack up your existing aquastat...
I got it now, thanks. I assumed they may have changed something on the boiler, but now that I understand how aquastats work, I see they didn't.

What do you mean be "in the same fashion as the aquastat would if the circ were still connected to it"? What circ, for the tankless? There is no such thing. Sorry for all the questions, I love learning!
 
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Old 12-20-07, 03:41 PM
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Originally Posted by StevenG View Post
What do you mean be "in the same fashion as the aquastat would if the circ were still connected to it"? What circ, for the tankless? There is no such thing. Sorry for all the questions, I love learning!
Not 'zackly sure I understand the question... but:

If it were a single zone system, there would be a system circulator connected to the aquastat. ( terminals C1 and C2 ) . On a warm-start boiler, that circulator won't run until the water temp gets above the LOW limit setting (+ diff).

By wiring the 506 panel for Tankless, you would preserve that 'behaviour' on the individual zone circulators. None of them would run until the water was hot enough.

If you left the old aquastat, but wired the 506 for cold-start, the zone circs would run immediately on a call for heat, but the boiler will still be kept warm.

Is that what you were asking ?
 
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