How do you connect two boilers?

I am looking for some advice as to the best way to connect a new AHS 130 to my existing propane boiler. The diagram provided on the AHS website seems backwards to me. My new coal boiler will set about 30 feet form my propane unit and will be used in the winter only. Would you recommend PEX tubing or copper, where would be the best location for the circulating pump, what about isolation valves...? Any help or advice would be greatly appreciated.

Thanks,
Dwayne

Dott727 wrote:I am looking for some advice as to the best way to connect a new AHS 130 to my existing propane boiler. The diagram provided on the AHS website seems backwards to me. My new coal boiler will set about 30 feet form my propane unit and will be used in the winter only. Would you recommend PEX tubing or copper, where would be the best location for the circulating pump, what about isolation valves...? Any help or advice would be greatly appreciated.

I have about 4 ways to plumb it depending on what you want to accomplish. I will post them tonight when I get home.

The distance between boilers is not a concern.
I would not use PEX, copper only.

Do you have a seperate water heater or tankless coil?

Our house is approx. 7 years old with staple-up in floor heat and one "bonus room" with baseboard. We have an indirect water heater. There are mixing valves on all of the in floor zones.

I am averaging 1750 gallons of propane a year, thus the reason for the coal boiler.

I am looking to use this as my primary heat in the winter with the propane as a back-up. Will the distance between the boilers affect the size of pump needed between the units?

I appreciate all of the help.

Thanks,

Dwayne

You should not use PEX tubing, use copper. How you pipe the two together will depend on what you are trying to do. Even though you have said you will only use the AHS 130 in winter I would suggest you pipe it so you can use it all year long. Depending on your fuel costs coal vs. propane it may be cheaper to heat your domestic hot water in the summer with coal. If not now perhaps in the future. I piped my S-130 in series with my oil boiler and have ball valves to isolate the coal boiler if needed. This way I can heat my coal boiler in summer eliminating the moisture rusting problem. Adjusting the valves controls the amount of summer heat. Circulation pump should be in the supply piping to your radiators or baseboard units right after the air trap.

Other considerations. Do you want automatic switch over to propane if the coal fire goes out? Do you need the BTU output of both boilers on a very, very cold day? Can your propane boiler run without electricity? If so, pipe it to be a no power backup. If you have lots of uninsulated piping the room above the boiler room gets too hot. Consider a indoor/outdoor aquastat to extend the coal use season. Helps the "it's to hot" problem. Be sure to size you expansion tank for the combined water volume. Think through valving off a hot boiler and how water from an expansion tank will now get back to the cooling boiler.

Sufferin' succatash! I can't figure out how to load these things. They are scanned as photos. Should I rescan as something else? And how? This is starting to look like the computer that needs a hammer.

If you PM an E-mail I think I can attatch it. The file is to big I guess.

Yanche wrote:You should not use PEX tubing, use copper. How you pipe the two together will depend on what you are trying to do. Even though you have said you will only use the AHS 130 in winter I would suggest you pipe it so you can use it all year long. Depending on your fuel costs coal vs. propane it may be cheaper to heat your domestic hot water in the summer with coal. If not now perhaps in the future. I piped my S-130 in series with my oil boiler and have ball valves to isolate the coal boiler if needed. This way I can heat my coal boiler in summer eliminating the moisture rusting problem. Adjusting the valves controls the amount of summer heat. Circulation pump should be in the supply piping to your radiators or baseboard units right after the air trap.

Other considerations. Do you want automatic switch over to propane if the coal fire goes out? Do you need the BTU output of both boilers on a very, very cold day? Can your propane boiler run without electricity? If so, pipe it to be a no power backup. If you have lots of uninsulated piping the room above the boiler room gets too hot. Consider a indoor/outdoor aquastat to extend the coal use season. Helps the "it's to hot" problem. Be sure to size you expansion tank for the combined water volume. Think through valving off a hot boiler and how water from an expansion tank will now get back to the cooling boiler.

When I looked at the AHS diagram on their website, they show the boilers in parallel. What are the advantages of series vs. parallel, and when you connect them in series, do you go from the supply of the coal to the return of the propane and the supply of the propane to the return of the coal?
I want my propane unit to take over if the coal boiler goes out or if I go away. I dont believe that I would need BTU output form both boilers.
I have circulating pumps on the supplys of each individual zone, but shouldnt there also be a pump that continuously circulates water between the boilers?
A diagram would be helpful.

Thanks for your help,

Dwayne

Hello Dwayne I would put the boilers in series. Have the cold returns from the existing zones enter the AHS, be heated by coal, then the output or supply side of the AHS go to the return/input side of the propane boiler.

Adjust the aquastat settings of the propane boiler to be 30*-40* lower than the water temp of the AHS. This seems like a lot, but if all the zones called for heat at the same time, it will take the AHS a few minutes to ramp up it's BTU output to satisfy the demand. If the Propane boiler was set too close the the low limit on the AHS, then the propane may kick on and you may not want it to.

I don't have my coal boiler in the basement next to my propane boiler, but I do have my coal heated water/water heat exchanger next to the Propane boiler, and the cold water return manifold goes through the heat exchanger then through the propane boiler then out to the zones in the house. Same setup, just with a remote heat exchanger instead of the actual boiler.

I think this is the most effective way to use the propane boiler as a backup, if the coal fire goes out, the water will still circulate the same way, it will just be heated by propane instead of coal.

Since you have a circulator for each zone, you should not need to add a circulator between the boilers. Assuming that the propane boiler won't fire until a thermostat calls for heat, then the AHS should supply hot water to satisfy a cold propane boiler within a few seconds of any zone circulator turning on. If not you can get electronic delay devices to provide a delay to the propane burner. Or provide a pasive return line between the two boilers, this should keep them both warm.

If you don't have an electric damper on the propane boiler, you may want to consider installing one, triggered to open with the propane burning coming on. This way you won't have a cooling draft pulling heat off the boiler all the time it is warm.


Greg L.

I am taking a slightly different approach to installing an AHS boiler to an existing installation that includes an oil fired boiler.

I am installing a controller that will sense the temperature of the water in the AHS boiler and when the AHS boiler has hot water and there is a demand from heat will activate a circulating pump to bring the hot water from the AHS boiler to the output side of the oil fired boiler. If the AHS boiler is not hot then the control will apply power to the burner of my oil fired boiler and it will operate normally.

I am using the following single pole double throw control that costs about $60.

http://www.honeyrunapiaries.com/store/r ... -p-86.html

Edited by the admin cause the files were huge and not needed.

If you leave your existing system alone and plumb a loop between the boilers using a reverse flow and check valves, the circulator on the coal boiler should run once the coal boiler makes minimum temp (this should be just above your existing systems temperature fall to fire point). If you have a tankless coil or draw water off your boiler for your domestic you will now get it heated with coal. In addition your existing unit remains up to temperature at all times and will fire when the coal boiler falls below its minimum temp and the circulator will stop. Totally auto with no wiring between them.

Didn't your AHS come with an Aquastat?

coaledsweat wrote:If you leave your existing system alone and plumb a loop between the boilers using a reverse flow and check valves, the circulator on the coal boiler should run once the coal boiler makes minimum temp (this should be just above your existing systems temperature fall to fire point). If you have a tankless coil or draw water off your boiler for your domestic you will now get it heated with coal. In addition your existing unit remains up to temperature at all times and will fire when the coal boiler falls below its minimum temp and the circulator will stop. Totally auto with no wiring between them.

Didn't your AHS come with an Aquastat?

Ugh, what a week,

Yes, the AHS did come with an aquastat. What you are describing sounds like what AHS shows in there manual, connecting the units in parallel. I did not purchase the tankless domestic coil, I have an indirect fired water heater. Are there any disadvanages to plumbing the units this way? If you connect them in series and dont use the coal boiler in the summer, I will have to heat the coal boiler with propane in the summer.

Thanks for all the help,

Dwayne

The AHS comes standard with an Aquastat and a second over temperature temperature switch. I would pipe the two boilers in series with isolating ball valves on the coal boiler and a valved bypass pipe shunting the supply and return. In winter the bypass is closed, the boilers are in series and your control system can provide automatic switch over if the coal fire goes out. In summer close the supply and return valves and open the bypass valve. Now only your non coal boiler is heating your indirect hot water heater. This is how my system is piped. Works well. I find that by partially opening only the supply valve in summer I can get enough heat, by gravity flow, into the coal boiler to prevent condensation. This is desirable depending on your summertime relative humidity and how prone to corrosion your boiler is.

Yanche wrote:The AHS comes standard with an Aquastat and a second over temperature temperature switch. I would pipe the two boilers in series with isolating ball valves on the coal boiler and a valved bypass pipe shunting the supply and return. In winter the bypass is closed, the boilers are in series and your control system can provide automatic switch over if the coal fire goes out. In summer close the supply and return valves and open the bypass valve. Now only your non coal boiler is heating your indirect hot water heater. This is how my system is piped. Works well. I find that by partially opening only the supply valve in summer I can get enough heat, by gravity flow, into the coal boiler to prevent condensation. This is desirable depending on your summertime relative humidity and how prone to corrosion your boiler is.

My boilers will be 30-40 feet apart. Do you think it would be necessary to install an additional pump?

Dott727 wrote:

Yanche wrote:The AHS comes standard with an Aquastat and a second over temperature temperature switch. I would pipe the two boilers in series with isolating ball valves on the coal boiler and a valved bypass pipe shunting the supply and return. In winter the bypass is closed, the boilers are in series and your control system can provide automatic switch over if the coal fire goes out. In summer close the supply and return valves and open the bypass valve. Now only your non coal boiler is heating your indirect hot water heater. This is how my system is piped. Works well. I find that by partially opening only the supply valve in summer I can get enough heat, by gravity flow, into the coal boiler to prevent condensation. This is desirable depending on your summertime relative humidity and how prone to corrosion your boiler is.

My boilers will be 30-40 feet apart. Do you think it would be necessary to install an additional pump?

No. You will have the additional friction losses of the piping and the elbows but you are not adding to the "head". Should work fine. Rule of thumb is to use piping no less than one pipe size below the supply and/or return fittings. I'm more conservative and use the same size. For the AHS S-130, it's 1-1/2 inch.

Dott727 wrote:Are there any disadvanages to plumbing the units this way? If you connect them in series and dont use the coal boiler in the summer, I will have to heat the coal boiler with propane in the summer.

A few advantages is you heat your domestic hot water with coal and keep your propane boiler up to temp at all times and it simplifies the control. When not in use, isolation valves will stop the transfer of heat to the coal boiler.