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Old 11-21-2013, 03:29 AM   #1
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Need input on indirect fired water heater install.


Hi,

I'm in dire need of a new water heater, and having done some homework, I believe that an indirect fired heater is what I need. I'm about 97% sure I'm going to tackle this on my own, and I'd like a little input on what I have planned.

Here's what I have now:

1200 sq ft single story house.
90K BTU gas boiler.
Single zone, no zone valves
Grundfos 20-42 circulating pump.
Honeywell L8148E Aquastat (no low limit switch) .

I haven't purchased the heater yet, but am likely going to get a HTP Superstor SSU30.

Here's what my plans are so far:

Use existing boiler, circulator and aquastat.

add second zone for water heater to existing loop.

Put a Taco 570 series valve on each loop.

Install 24VAC transformer to power the valves.

Connect #2 and #3 terminals on both zone valves to Thermostat terminals on boiler aquastat.

Connect house thermostat to terminals #1 and #2 on the house zone valve.

My understanding of how that will operate:

House temp drops below setting, House thermostat closes switch on house zone valve circuit. Zone valve opens, and also closes switch across terminals #2 and #3, which closes thermostat circuit on aquastat. Aquastat turns on boiler burner and turns on circulation pump. house reaches temp, thermostat opens, zone valve closes, aquastat turns off burner and circulation pump.


For the water heater, I'm a little fuzzy on whether it comes with a temp control or that's a separate install. That's another question for my supplier. But, either way, my assumption is that it's just another switch, like the house thermostat. So, installation and operation will be similar to house zone, except it regulates temp of the water in the tank rather than the temp of the air in the house. Is that a correct assumption, or are there some differences I'm missing there?

My supplier has recommended setting this all up with a zone controller, so that the heater zone can be given priority. I understood this to mean that if both the heater thermostat/aquastat was calling for heat and the house thermostat was calling for heat, the heater zone valve would open and the house zone valve would not, and this is to improve recovery time on the water heater. Meanwhile the house would not heat until the water heater was recovered to temp. Am I understanding this correctly?

My take on this is that I don't need the zone controller. For my particular household, hot water demands aren't large and sustained, so I'm inclined to do this with just the zone valves and thermostats/aquastats, with the understanding that water heater recovery will not be as quick as it could be. If I discover that I'm not happy with the recovery I can always retrofit the zone controller, and the only thing I'll be out is I'll have an extra 24VAC transformer that I don't need anymore.

BTW, there's a 24VAC transformer in the boiler aquastat, but as far as I can see this can't be used to operate the zone valves, they need a separate transformer, correct?

So, are there any fatal flaws in my plan? Things I've overlooked? Things I think I understand but don't? I'd be interested in any and all input here.

FWIW, I'm also planning on installing a mixing valve for the domestic hot water supply.

Thanks


Last edited by A Squared; 11-21-2013 at 03:31 AM.
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Old 11-21-2013, 05:59 AM   #2
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Need input on indirect fired water heater install.


The thermostat doesn't wire to terminal 1 and 2 of the Taco powerhead. A wire from the transformer goes to the R of the tstat, and then the tstats W terminal connects to 1 of the powerhead. Then a wire from terminal 2 of the powerhead goes back to the transformer.

Does the water coming out of the boiler ever get cold when the thermostat first calls for heat. Or does it come out hot right a way. If it comes out cold. Imagine your in the shower and the thermostat calls to heat the house and the indirect also calls at the same time. Not only will it take longer to heat the indirect, but it will cool the water in the indirect because the indirect will be heating the water in the boiler and your baseboard/radiators.

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Old 11-21-2013, 06:32 AM   #3
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Need input on indirect fired water heater install.


Quote:
Originally Posted by beenthere View Post
The thermostat doesn't wire to terminal 1 and 2 of the Taco powerhead. A wire from the transformer goes to the R of the tstat, and then the tstats W terminal connects to 1 of the powerhead. Then a wire from terminal 2 of the powerhead goes back to the transformer.
Agree the thermostat should complete the circuit with the transformer through the #1 and #2 terminals. I was a little sloppy when I typed that the first time, and it came out incorrectly.



Quote:
Originally Posted by beenthere View Post
Does the water coming out of the boiler ever get cold when the thermostat first calls for heat. Or does it come out hot right a way. If it comes out cold. Imagine your in the shower and the thermostat calls to heat the house and the indirect also calls at the same time. Not only will it take longer to heat the indirect, but it will cool the water in the indirect because the indirect will be heating the water in the boiler and your baseboard/radiators.
Good question. I never checked that specifically, but as far as I know, the burner doesn't fire unless there's a call for heat, and a call for heat powers the pump immediately, so if it's been a while since the last call for heat, the water would probably be cool at first.

I see your point about cooling the water in the heater at first, but even if I were to use a zone controller with priority on the water heater zone, it seems that would still happen, although not as much.

Is there a way to eliminate this effect entirely?
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Old 11-21-2013, 07:28 AM   #4
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Need input on indirect fired water heater install.


In your post you stated that the hot water demand would not be that great and not for a long time.

Sounds like a lot of controls, valves and things to go wrong with the amount of hot water needed.

I would look into a much simpler system to pair with my main heater.
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Old 11-21-2013, 02:10 PM   #5
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Need input on indirect fired water heater install.


Quote:
Originally Posted by COLDIRON View Post
In your post you stated that the hot water demand would not be that great and not for a long time.
By that I meant that I didn't have a family of 5 who all wanted showers between 0630 and 0715 each morning. There's 2 people living there with differing schedules, so recovery isn't a crucial factor.


Quote:
Originally Posted by COLDIRON View Post
I would look into a much simpler system to pair with my main heater.
I agree that simpler is better, but I haven't been able to identify a simpler system that fits my particular constraints. If there was a drop-in replacement for my current gas fired heater, it would already be installed and we wouldn't be having this conversation. My heater is in my crawl space which is height limited. Currently it's a short, fat gas fired heater, but gas heaters are no longer made with those proportions because they are less efficient. Believe me, I've looked high and low for a gas heater which will fit. As far as I can tell, they don't exist anymore. I could get an Electric heater which would fit in the space, but Electricity is expensive and gas is inexpensive here so that would be a poor choice economically. I have no other good location to install a tall gas heater. I've looked into on-demand systems, including getting estimates for installation. Between having to re-do my 1/2" gas supply with 3/4" pipe all the way form the service connect, and having to run propitiatory (read expensive) venting a long way to an exterior wall, it would be pretty expensive. I actually thought at one time that an on-demand system would be the best choice until I started researching the characteristics if the system and the installation required.

If you know of a simpler system I've overlooked, or know of a simpler way to install an indirect heater, I'm all ears.
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Old 11-21-2013, 06:25 PM   #6
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Need input on indirect fired water heater install.


With priority the boiler will warm up much faster then trying to heat the house. So you won't notice the cold start. If its doing both at the same time, you will notice the water cooling.

Remember, priority usually is limited to 30 minutes then it switches to heating the house.
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Old 11-23-2013, 02:07 AM   #7
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Need input on indirect fired water heater install.


Thanks, beenthere. that weighs the balance a little more toward a zone controller. I'll keep that in mind.
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Old 11-23-2013, 10:29 AM   #8
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Need input on indirect fired water heater install.


I'd consider the cost to install verses lifetime costs of an indirect and electric.

The cost to operate an electric water heater that has a good amount of extra insulation wrapped around it and maybe even a timer to only allow it to heat only when there is a chance someone will need a full draw of hot water is not that bad. Cost of an electric verses the indirect in most cases is going to be substantially less, not to mention the other components needed for the indirect. Every component adds another potential failure and cost to repair/replace to the life costs.

Depending on the efficiency of your boiler, the style/model, and the conditions it will be operating in during the non-heating months..... the addition of the indirect is going to add complexity to the heating system and shorten the life of the boiler due to more run time. These "costs" should be looked at also.

When the indirect calls for heat in the non-heating season the boiler is going to be cold and will absorb heat from the water heater until such time as the burner has put enough energy into the water to reverse the flow of heat back into the indirect. This can be resolved with controls, but adds complexity and cost to the system.

Just some thoughts.
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Old 11-23-2013, 10:48 AM   #9
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Need input on indirect fired water heater install.


Quote:
Originally Posted by old_squid View Post
I'd consider the cost to install verses lifetime costs of an indirect and electric.

The cost to operate an electric water heater that has a good amount of extra insulation wrapped around it and maybe even a timer to only allow it to heat only when there is a chance someone will need a full draw of hot water is not that bad. Cost of an electric verses the indirect in most cases is going to be substantially less, not to mention the other components needed for the indirect. Every component adds another potential failure and cost to repair/replace to the life costs.

Depending on the efficiency of your boiler, the style/model, and the conditions it will be operating in during the non-heating months..... the addition of the indirect is going to add complexity to the heating system and shorten the life of the boiler due to more run time. These "costs" should be looked at also.

When the indirect calls for heat in the non-heating season the boiler is going to be cold and will absorb heat from the water heater until such time as the burner has put enough energy into the water to reverse the flow of heat back into the indirect. This can be resolved with controls, but adds complexity and cost to the system.

Just some thoughts.
I agree, good thoughts. Keep it simple.
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Old 11-23-2013, 12:10 PM   #10
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Need input on indirect fired water heater install.


Quote:
Originally Posted by old_squid View Post
I'd consider the cost to install verses lifetime costs of an indirect and electric.

The cost to operate an electric water heater that has a good amount of extra insulation wrapped around it and maybe even a timer to only allow it to heat only when there is a chance someone will need a full draw of hot water is not that bad. Cost of an electric verses the indirect in most cases is going to be substantially less, not to mention the other components needed for the indirect. Every component adds another potential failure and cost to repair/replace to the life costs.

Depending on the efficiency of your boiler, the style/model, and the conditions it will be operating in during the non-heating months..... the addition of the indirect is going to add complexity to the heating system and shorten the life of the boiler due to more run time. These "costs" should be looked at also.

When the indirect calls for heat in the non-heating season the boiler is going to be cold and will absorb heat from the water heater until such time as the burner has put enough energy into the water to reverse the flow of heat back into the indirect. This can be resolved with controls, but adds complexity and cost to the system.

Just some thoughts.
Considering that his area has a relatively low gas rate compared to its electric rate. A family of 4 that only takes 4 showers a day, and only uses 10 gallons of hot water per shower. If both the water heater and indirect only heat up the 10 gallons of water being used per shower. An electric water heater will cost 257 dollars a year more to use. This doesn't include any hot water for cooking, washing dishes, cloths washing, or general house cleaning. Nor any stand by losses. Which both methods of water heating will have.
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Old 11-23-2013, 01:43 PM   #11
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Need input on indirect fired water heater install.


It's all relative, maintenance costs, things to go wrong with a more complicated system with more controls and breakdowns.

The set point on the water heater, maybe 4 people are not taking a shower every day in Alaska.

A lot depends if it cost more per year gas vs Elec.

I say install a standard electric water heater with good insulation and keep it at 120DEG. and keep it separate from the Main house system.
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Old 11-23-2013, 02:49 PM   #12
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Need input on indirect fired water heater install.


Thanks guys. While I appreciate the suggestions to re-examine the choice of overall method, these are things which i have already considered.

Yes, an electric water heater would be simpler and less expensive to purchase and install. It would not be less expensive to operate. Like I've said, gas is chap and electricity is expensive here. I've already run the numbers for the options and the additional cost for an indirect gas system will be recouped fairly soon.

Additionally, Alaska has a home energy improvement program under which I may be able to get rebates for installing an indirect heater. I can tell you there is no credit for installing electric water heaters.

As far as the comments about the complexity, I'm not really seeing that this is an overwhelming concern. Compared to installing an electric heater, the only additional "complexity' is 2 Zone valves and a transformer. Or if I change my mind on the zone controller it's 2 zone valves and a zone controller. Zone valves are butt-simple devices, and while anything can fail, the powerhead can be changed in less than a minute by twisting it a quarter turn and disconnecting 2 wires. The zone controller is a single solid state circuit board with a transformer and some relays. We're just not talking about a lot of complicated equipment here. As far as I know, none of the additional equipment has a lot of (any) required maintenance. If it breaks, replace it. Other than that there's nothing to lube,clean, adjust, tighten or refill.

Believe me, when I realized that I wasn't going to be able to buy a replacement gas heater which I could install where the failing one is now, I took a long hard look at an electric replacement, as electric would be the easiest option with the lowest initial acquisition cost. I appreciate the comments, but I didn't select an indirect system without pretty careful consideration.
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Old 11-23-2013, 04:38 PM   #13
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Need input on indirect fired water heater install.


An indirect, zone panel, zone valve, and circulator, all have longer life spans then the average electric water heater.
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Old 11-23-2013, 05:42 PM   #14
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Need input on indirect fired water heater install.


Your money, your house , your system sounds like you have a good handle on what you want to put in. Go for it.

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