Indirect water heater questions

Hi, I live in Long Island, NY. My current heating system is a 50+ year old American Standard boiler with a Beckett oil-fired burner. Attached to it is an uninsulated indirect water heater of unknown brand (which is probably as old as the boiler). Most of the system is as old as the house, which was built in the early 50s (the burner and a couple of the circulators are fairly new).
For some reason, the previous homeowner (who was also the homebuilder) connected the indirect water heater to the hot water coil of the boiler, rather than using the recirculated boiler water. The system had been working fairly well, although I suspect not at top efficiency (we had insulated the water heater using a fiberglass water heater blanket, but there was still some heat leakage out the top).
Anyway, recently, we've been having problems with the boiler pressure triggering the pressure relief valve. After I empty the expansion tank, the pressure gauge goes down to a more reasonable level; a couple of weeks later and the pressure is high again. Our serviceman came out and told us that there is a crack in the hot water coil (I'm not sure how he concluded this, as I wasn't home at the time, and I didn't think to ask). Now, since indirect water heaters don't require a hot water coil (and when I tried to run our domestic HW directly through the coil, the pressure was awful), I'm thinking I can just plug the HWC and attach the water heater directly to the boiler. Now the questions ensue:
1. Is the conclusion about the cracked hot water coil valid? Is there anything else that might cause this situation (boiler temperature is being regulated properly at 160F)?
2. I'm thinking that since I'm doing some major work on the system, I might as well replace the indirect water heater at the same time (I don't want to get involved in replacing the boiler; I know it's not the most efficient but that would incur enormous expense which would probably not be recovered for a couple of decades; the sytem has been fairly reliable except for this issue). I've noticed there are two major types: most have a large recirculated-water tank with a coil for domestic water; however, Phase III (and possibly other) heaters have an outer and inner tank (this is how I had assumed they were all constructed before I started doing research). Is there any advantage of one over the other? The Phase III heaters have a much larger domestic tank than recirculated-water tank.
3. The installation instructions for the Phase III heater explicitly specify not to plug the old hot water coil (their exact words: "Plugging tankless coil inlet and outlet will [sic] result in severe personal injury, death, or substantial property damage."). Now first, it seems to me that if the coil is completely purged of water, the only thing in it will be air, and expanding air won't be enough to rupture the coil. Additionally, I've seen similar systems in other homes where the HWC HAD been plugged; also, since our coil is already cracked, additional damage will be minimal or non-existent. Thoughts?
4. The house is a two-family home; figure average occupancy is 6 people (adults+children). Any way I can easily calculate the size heater I need?
Post responses to the groups, please; this email address is now owned by the spammers.
Thanks,
Steve
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Steve wrote:

<SNIP>
The other possibility is that the boiler feedwater valve is leaking (i.e., not closing tightly) allowing a trickle of water into the boiler day and night. Look for a shutoff valve so you can isolate that as a cause.
former LI'er
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My thought on the cracked coil would be that if it is cracked you should see water leaking. And if it is cracked, then you will most likely be getting boiler hot water into your domestic hot water. Is your hot water brown or dirty looking? As for the pressure relief valve. Check your automatic fill valve. It may need to be replaced. Depending on your water, the valve may be stuck open a liitle causing your boiler to fill and raise the pressure. I'd replace it or better yet, open it up and look to see if there is a lot of crud in it.
If the boiler is 50 + years old you still may want to consider replacing it. I replace them, depending of the BTU's and # of zones, for around 3 - 4K complete. Your savings should be made up in a couple of years because of the effiency.
A new 40 to 50 gal indirect DHW can run about 600 - 1K depending on model.
Paul
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On 8 Mar 2006 11:58:14 -0800, someone wrote:

it is surrounded by boiler water, where would one see a leak? (Really, if there is someplace, I'd like to know, I've seen this situation and there was no visible leak anywhere external.)

domestic water is often around say 60 psi and a low pressure residential boiler nowhere near that. But, I'm not sure I'm getting how his indirect tank is plumbed - was it the FEED coming off the domestic coil, or was it the CIRCULATION?

coil was indeed the domestic feed at domestic pressure), causing higher pressure water to seep into the boiler thus over-filling it????
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whether you replace this old boiler and water heater or continue inefficiently operating it as an antique with a full set of new safe replacement controls and energy star rated circulating pumps is up to you. :) who: i'm not the hvac expert for this. what: is the combustion efficiency of your model number? maybe 50-60 percent? where you live, the climate: what is the energy source of least expense for this heating task in your city? when: you need to do this is either at the hvac company's convenience instead of rushing the job, while you monitor the pressure and leakage problems and get a headache, or as soon as you shake some money out of your budget for this home improvement. why: for year-round comfort and energy savings. how: keep doing the homework. is it still true that there are no high efficiency boilers for oil, only natural gas? can you install central air and an efficient gas furnace? nice central air conditioning may be the wonderful summer benefit that awaits you. the new insulation package you install into your home will affect your btu calculations. see: http://www.buildingscience.com/resources /
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"3. The installation instructions for the Phase III heater explicitly specify not to plug the old hot water coil (their exact words: "Plugging tankless coil inlet and outlet will [sic] result in severe personal injury, death, or substantial property damage."). Now first, it seems to me that if the coil is completely purged of water, the only thing in it will be air, and expanding air won't be enough to rupture the coil. Additionally, I've seen similar systems in other homes where the HWC HAD been plugged; also, since our coil is already cracked, additional damage will be minimal or non-existent. Thoughts? "
If the existing in-boiler hot-water coil resides INSIDE the water in the boiler, if it leaks it will fill with water. Plugging it in that case could be bad news.
Leaving it open would mean water would be forced out of it, the rate depending on the size of the leak.
You could T the 2 ends of the coil together and connect the 3rd leg of the T to a std pressure relief valve, or you could connect the 3rd side of the T to one of the boiler-water legs, but it all seems somewhat of a hack.
If the coil is not submerged in the boiler water, it would seem OK to plug it (otherwise you'd get fumes through the leak), but I'd seek professional help considering all the questions involved.
dave
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Answer to question 1
There are two ways the boiler could be gaining pressure. The first one is that there could be a leak in the domestic hot water coil. The other is the pressure reducing boiler feed valve is bad. The easy way to test this is to shut off the water feed to the boiler and see if the pressure in the boiler continues to clime. If it does than the domestic hot water coil is bad.
Answer to question 2
There is no real advantage in either a submersed coil or a tank with in a tank. What you need to look at is the recovery time of the tank in regard to the size of the boiler.
Answer to question 3
If the coil is leaking you have to plug it. I ran an oil boiler for years with cracked coil that was plugged. One way to be safe with the plugging of the coil is to drill a small hole in the coil to relive any pressure that could build up. This can be done with a long drill bit with out removing the coil.
Answer to question 4
A 60-gallon indirect water heater turned up to 140 degrees with a mixing valve installed on it set at 118 should work fine.
The tank on the system now may not be an indirect tank. It may be just a storage tank using the coil in the boiler to keep the domestic water separated from the boiler water. Quite frankly I would change out the boiler and the tank at the same time. The boiler is now keeps a constant 140 to 160 degrees all year long. This is a HUGE waste of energy considering the age of the equipment. Changing the boiler to a cold start boiler is not recommended as it may start to leak. I will add some info on European boilers and indirect tanks below.
Gary J
This is the link to the page where you can find info about some Indirect Fired Hot Water Tanks Just double click on it or cut and paste it into your browser.
http://www.houseneeds.com/shop/HeatingProducts/boilers/indirecttanks/indirect-storage-tanks-index.asp
Below is information that will explain the efficiency questions many people have on boilers. After you have read through the material, please check the links provided to some of our Oil Boiler resources.
European oil boilers VS American oil boilers.
AFUE Ratings: The US method for establishing efficiency is the Annual Fuel Utilization Efficiency rating, or AFUE. This method has serious flaws as looks at only steady state combustion to determine the overall system efficiency. No consideration is given to system mass, boiler design and materials, off cycle cooling, jacket heat losses, the common method of installation, or the manner in which the boiler is operated. The major rating flaws are as follows:
The boiler combustion is typically tested at 12.5-13.0% CO2 which is the range where the equipment should operate for maximum heat release from the fuel. However, to reduce field problems due to poor boiler design and serviceability limitations, the US manufacturers instruct the installers to run the boilers at 10.5-11.0% CO2. As CO2 is actually a measurement of flame (chamber) temperature, dropping the CO2 reduces the temperatures by 250-300, and, conversely, increases the stack temperature by 150-200. Most US boilers carry multiple boiler ratings for a single unit. The AFUE testing is typically done at the lowest firing rate, which drops the stack temperature, and enhances the testing. However, in actual installations, the higher firing rates are typically used, increasing the flue temperatures to 450-550, which reduces the actual field operating efficiencies.
Boiler testing is accomplished at "steady state", with the boiler operating between the aquastat set points. During the AFUE testing, very little consideration is given to off cycle cooling. The standard "pin type" US boiler requires a chamber that is open to the chimney, and is subject to the negative draft created by the chimney. This creates a situation where the chimney basically vacuums the heat from the chamber, both during operation, creating high stack temperatures, and during the off cycle, creating continuous cooling of the appliance.
Also not considered during the qualification testing is boiler design or mass. The typical "pin type" boiler is a single pass design, with a mass weight of cast iron and water in excess of 650 lbs, and a chamber flue pass age length of approximately 2.5'-3'.
The bottom line is that boiler design is in reality simple physics, and this tells us that the larger the mass, the more Btu's you need, and therefore, the more fuel consumed. Also, the shorter the flue passes, the less cross sectional area and time you have for heat absorption.
Finally, there are other issues not seriously considered in the AFUE rating system, such as jacket heat loss, which can exceed 5%of the available Btu's, or the radiational cooling effect of the barometric damper, which is required for safe operation on single pass boilers.
In the final analysis, considering all the factors presented, although a conventional boiler can demonstrate an AFUE rating of 82-84%, the actual thermal efficiency of these units can be as low as 56%.
A Better Efficiency Model: The Europeans, who every day face energy costs 2-3 times higher than the US, have developed significantly more efficient equipment, and a much more accurate system for determining the actual efficiency. Their rating system looks at all aspects of thermal efficiency, and current efficiency requirements for boilers exceed 89% for the entire system. The major rating requirements are as follows:
All boilers must operate during testing and in the field at 13.0+ % Co2, which allows for maximum heat release from the fuel. This performance level is verified during the annual field efficiency test, which is mandated by the manufacture, and verified by law. The standard boiler design is very tight, creating a forced draft situation which compresses the flame in the chamber, and releases the maximum Btu's.
European standards require a single firing rate for each boiler, which typically is the maximally efficient rate for that boiler. These rates are verified during testing, and, again, during the annual field efficiency testing.
It is mandatory that European cast iron boilers be manufactured from GG20 cast, which is flexible and allows for low return water temperatures without damaging the boiler. Control schemes such as cold start, and outside temperature reset are common, and their efficiencies are verified during testing. The testing procedures even include the total electrical draw of the burners, circulators, etc., so low amperage draw units are common.
The standard European boiler design is a multi-pass, forced draft unit, which is very tight, and is insulated from the chimney draw. The burner is required to force the flue gasses thru the system, and therefore, when the burner is off there is very little off cycle temperature loss, as the chimney cannot draw on the chamber. Close up of the Biasi burner system
A 3-pass boiler design is the most efficient way to get the maximum amount of heat from the fuel, since it contains three times as much interior surface area (compared to a single-pass boiler) to extract heat from.
In addition, during the operating cycle, the flue temperatures range from 325-350 and consist of Btu's not absorbed due to other system considerations such as chimney condensation, fuel constituents, etc.
These boilers are low mass, multi-pass units which weigh 50% less than conventional pin type boilers, and typically have water contents 50-60% lower. This yields a total mass considerably lower than pin boilers, and requires considerably less fuel to operate, which again, is simple physics. It is not uncommon to see a 100,000 Btu system with a total mass of 347. In addition, as these units are at least three pass by design, the actual flue passage lengths are 6'-7', which provides for a much longer flue gas contact time, and substantial heat absorption.
Serious consideration is given to issues such as jacket loss, and other installation requirements like barometric dampers, which rob heat from the system. The typical European boiler has a 3" insulation blanket, wrapped over the boiler block, which virtually eliminates jacket loss, and keeps the heat in the boiler where it belongs. The barometric damper is used only where other installation considerations, such as a low or high draft chimney, are present, or, in the case of natural gas, where a double acting barometric is required by code.
Taking all these facts into consideration, most European boilers end up with an AFUE rating exceeding 87%, and a real thermal efficiency in the range of 83-85%. The difference between the efficiency of pin type boilers, and low mass, multi-pass boilers can easily exceed an annual fuel savings of 30-40%. In addition, as there are low Nox units, which meet or exceed all North American standards, now available, we can clean up the environment, while saving a ton of money.
This is the link to the page where you can find info about the BIASI Oil Boilers Just double click on it or cut and paste it into your browser.
http://www.houseneeds.com/shop/HeatingProducts/boilers/biasi/biasiboilermain.asp
Gary J
Steve wrote:

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