Standing pilot or spark ignition?


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Old 08-17-10, 07:04 PM
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Standing pilot or spark ignition?

Planning on a W-M CGa-4 boiler, trying to decide between standing pilot and spark ignition. Standing pilot seems to be cheaper and less maintenance heavy, spark ignition is a bit more fuel efficient.

I'm going to have an indirect DHW, so the fuel efficiency of spark ignition seems a bit less significant.

Thoughts?
 
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Old 08-17-10, 08:07 PM
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come on.
Spark ignition if you must go natural vent.

A pilot is a unessasary waste.
 
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Old 08-18-10, 03:13 AM
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Please remind me again why you are installing a mid-20th Century grade boiler in the 21st Century? A modcon would rock in your system. They have been around long enough to have a few that are above the rest, e.g., Triangle Tube, Vie$$mann, and are reliable and very efficient.
 
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Old 08-18-10, 12:42 PM
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My concern with modcon is cost (more than $1000 premium for a modcon over the cga-4), and, especially, maintenance. I've spoken to a few local heating folks, including _the_ big maintenance company for this area, that does most of the service contracts here (used to be part of the local gas utility till the state took over and broke it up), and none of them know a thing about modcons. Finding someone to service them who knows what they are doing is tough.

Also, my understanding is that modcons are generally very low thermal mass, whereas I'm trying to maximize the system thermal mass. Not sure if the modulating aspects of the boiler overcomes the lack of thermal mass.

The other issues is that my emphasis is more on comfort that energy efficiency. I doubt I'll be in this house long enough for the costs of the systems to pay back in energy savings, it's the comfort I'm going through. Most of the other things I'm doing (the outdoor reset, the small zones, the mixing reset) add to comfort, not just efficiency. I'm not sure that a modcon will add to the comfort of the system.
 
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Old 08-18-10, 01:44 PM
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Originally Posted by jgalak
trying to decide between standing pilot and spark ignition. Standing pilot seems to be cheaper and less maintenance heavy, spark ignition is a bit more fuel efficient.

I'm going to have an indirect DHW, so the fuel efficiency of spark ignition seems a bit less significant.
I think your evaluation of spark vs. standing pilot is correct. Not much that can be added.

Why does DHW make the fuel efficiency of spark ignition less significant? I would think it'd be the opposite - without DHW, you'd turn off the standing pilot during maybe half the year.
 
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Old 08-18-10, 02:25 PM
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Mike - I was thinking the opposite - without the DHW, I'd have the pilot burning half the year for no reason. Didn't occur to me that I could turn it off... Doh!
 
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Old 08-18-10, 02:40 PM
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By the way, I take it you have natural gas - and that your current indirect heater is good to go for quite a while?

I see that you live in the Northeast. The Northeast seems to be big on DHWs. OK, since much of that area uses fuel oil, it makes some sense.

Here in the Midwest, where natural gas is the fuel of choice and readily available in towns and cities, DHWs are unheard of. (And if natural gas happens to be unavailable, such as in rural areas, then propane is used, not oil.) Everybody uses a separate, stand-alone gas water heater. (The heating boiler is then shut down for half the year or so.) A standard glass-lined 40-gal gas water heater is pretty cheap and should last 15-20 years assuming that you're on city water.

My last water heater lasted 50 years, and still wasn't leaking - but maybe a bit past its prime. We're on softened city water, so it probably wasn't scaled up too badly. When I had that heater replaced about three years ago, they tried to sell me a super-duper gas water heater with all the latest 21st-Century features. No, just give me the standard, glass-lined, 40-gal heater with a standing pilot. (It does have push-button spark for relighting the pilot if it ever goes out - haven't had to use it yet.) Brand doesn't matter - many heaters are made in the same plant in Tennessee.

I use gas for space heating, water heating, outdoor grill, clothes dryer, and cooking. Based on my lowest summer usage, I estimate that we spend about $10, or a little less, per month for water heating. So, there you have it - hard to economize on that. Meanwhile, during the non-heating season, the boiler is as cold as a cucumber - not burning gas nor adding to the A/C load.
 

Last edited by Mike Speed 30; 08-18-10 at 04:06 PM.
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Old 08-18-10, 04:33 PM
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We currently have a 50 gallon gas-fired stand alone water heater. We routinely run out of hot water when my wife and I take showers (I tend to take very long showers, while she likes to take very hot ones, both seem to use much more hot water than normal...). I am planning to replace it with a 50 gallon indirect DHW heater, which should deliver 2-3 times as much hot water in a unit the same size. Additionally, the indirect is much more efficient than a standalone, but as I said above, that's not the primary goal.
 
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Old 08-18-10, 05:43 PM
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On the first cost, that is probably negated by federal tax credits, state credits, and/or utility rebates. See www.dsireusa.org for federal, state, and utility credits in your area. And the simple payback on fuel savings, even compared to a new, properly sized cast-iron fixed-fire boiler like the CGA, is probably fairly quick.

With a modcon, you also no longer need all that extra (~ $grand) worth of mixing reset, more sensors, pumps, yada yada. Set it up and go. The Triangle Tube boilers in particular marry well with external tekmar controls if you are going the tn2 or tn4 route. IIRC, the newer Vie$$mann 100s can support dual temperature zones right out of the box. Options abound.

Where do you live that no one does modcons? Modcons have been around long enough in general circulation. If the people you are talking to don't know or do modcons, then quite honestly they are 5-8 years behind the current standard in their trade and you don't want to deal with them anyway. The good modcons require predictable annual service. Properly installed and maintained, the fuel savings is greater than the annual maintenance. Just stick with the stainless heat exchanger modcons. Aluminum block modcons are another deal entirely (and IMHO, something to stay away from).

Yes, modcons are low thermal mass, but when you microzone and have small loads, you don't really want a huge thermal mass in the boiler block to have to heat up just to satisfy a small load. Thermal mass out in the distribution system (radiators) is where you get a lot of thermal mass bang for the buck. The boiler is just a quick pass-through to heat up the water. And with outdoor reset and proper dT, it doesn't need much contact time. Add modulation into the equation and now you are cooking with gas (as it were ). It's efficient and comfortable.
 
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Old 08-18-10, 06:28 PM
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Yeah, I was just re-doing the numbers with just that in mind. Between the federal tax credit (utility credits are too annoying to get here in NY) and the simpler system (less circulators, cheaper controller, etc.) the initial price is pretty much a wash. The fact that the system is simpler is a big plus, as I'm doing the work myself and time is the tightest commodity

The Triangle Tube Solo 110 looks perfect, but I do have one question: the install manual says to use a special pipe connection for the DHW, and to wire the DHW circulator to the boiler. I wanted to use the Tekmar to control the DHW circulator. Can I wire the circulator to the Tekmar and still use the special DHW pipe connection on the boiler?
 
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Old 08-18-10, 06:51 PM
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Originally Posted by jgalak
We currently have a 50 gallon gas-fired stand alone water heater. We routinely run out of hot water when my wife and I take showers (I tend to take very long showers, while she likes to take very hot ones, both seem to use much more hot water than normal...).
This seems unusual, but I don't doubt you. How old is the heater? Is it scaled up, by chance? Have you been draining a bucket full every month? Are you on city water?

During periods of high demand, the recovery time is as important as the gallon volume of the heater. What is the Btu/hr rating of your heater?

My wife and I take showers at the same time (in separate showers ) Never a lack for hot water. About once every six months, our kids and grandkids arrive - major hot water demand, and no problem with our 40-gal heater (40,000 Btu/hr, 41 gal/hr recovery).

You say that an indirect is much more efficient than a stand-alone water heater. I'm not so sure of that, but would be interested in your thinking. Consider that your big, oversized boiler (at least in the non-heating season) will be running all summer. And, consider my situation where I use less than $10 per month in gas for water heating. How much of that amount will an indirect save, if any?

And how much will you have to oversize your boiler to serve the indirect?

Me thinks that you may be listening to New England people? While working in Kansas City, I picked up a smart, educated, senior client flying in from Hartford, CT. As we drove from the K.C. airport toward our engineering office in the south part of the city, we crossed over the Missouri River. He asked if that was the same river that runs past Pittsburgh. I was stunned, speechless.
 

Last edited by Mike Speed 30; 08-18-10 at 07:24 PM.
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Old 08-18-10, 08:50 PM
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The boiler doesn't get oversized for the indirect DHW - it's generally put on a priority system where the heat will be diverted to the DHW from the space heating zones. With the Tekmar controller that's handled even better - it'll selectively shut down zones as needed (load shedding) to provide enough heat for the DHW.

The main reason that the indirect is more efficient is due to standby heat loss. In a standalone heater, the sides are insulated, but there is a "chimney" down the middle that is _not_ insulated from the water in the tank, and serves as a very effective heat loss path from the tank. As a result, the heater must constantly come back on to maintain temperature. In an indirect, otoh, there is no chimney, and the tank is well insulated from all sides. As a result, an indirect will have much lower standby losses. A friend of mine ran an experiment recently. According to his measurements, a standalone water heater lost about 1 degree F every 1-2 hours (no water being used and the gas turned off). A similar sized indirect tank lost about 1 degree F in 12 hours or so. Big difference.

Additionally, a typical gas boiler is far more efficient than the little burner in the bottom of the standalone heater. Typical efficiencies on gas water heaters are around 60-70% (although there are apparently some condensing models now that may be better, don't know much about them). Even a basic cast-iron boiler like I'm considering above should be around 85%. A mod-con could be 95%.

You are also absolutely correct about recovery time - and that's where the indirects really shine. An indirect lets you put the entire output of your boiler (around 70-80,000 BTUH) into the tank, as opposed to the much smaller output of a standalone heater.
 
 

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