Help with required component list and piping -oil to gas fired boiler conversion


Old 10-10-14, 11:56 AM
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Help with required component list and piping -oil to gas fired boiler conversion

I am in the process of converting from an oil-fired to gas boiler system in a 2 story house that was built in 1929 and have a few questions about piping and also what components are required.

I have removed the oil burner and tank, I also installed a SS chimney liner. Thanks to this forum, I also did a heat loss calculation and purchased a conventional 70K Input Btuh boiler.

My system appears to be fairly basic: my boiler supply feeds (2) ea. 1 1/2" diameter steel pipes and returns back with the same size piping. I have cast iron radiators on the second floor and cast iron baseboards on the first floor.

Here are my questions:

1) Is this system considered a "high water content system"? If so, I need to install boiler bypass piping, correct?

2) Is a separate universal flow check valve required for the boiler water, or can I just use one integrated into the circulator pump? If so, does it make sense to install the pump on the supply side -vs- the return?

3) Do you recommend isolation valves on both the supply and return boiler piping? The existing configuration has valves only on the return piping.

4) I was going to purchase the Extrol 30 expansion tank. Do you agree that it is sized correctly?

5) Is a backflow check valve required for the cold water boiler fill?

Thanks in advance for any help given!
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Old 10-10-14, 05:45 PM
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Yes, you have a high water volume system.

You may use either a separate flow control valve or a circulating pump with a built-in flow check. I prefer separate. The circulating pump ALWAYS needs to be installed with the expansion tank point of connection on the suction side of the pump.

Valves cost money but the more the better. Definitely have valves that allow complete isolation of the boiler and the circulation pump. Additional valves to allow isolation of the expansion tank for testing are desirable.

The size of the expansion tank is governed by the total volume of the entire system. A #30 may be adequate but I have no way of determining that with the information given.

The cold water fill requires an approved backflow preventer. If you are going to chemically treat the system then it needs a reduced pressure backflow preventer. Your LOCAL codes may dictate the type of backflow preventer required.
Old 10-13-14, 10:02 AM
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Thanks for the reply, Furd.

So, my system is a high water content system because of the 1 1/2" dia. supply and return piping? Does this mean that it used to be a gravity return system, originally (1n 1929)?

I picked up a two way flow check valve (Watts 2000-M5); my thinking is to use this to connect the boiler bypass and boiler supply and then to feed the system. This way I am able to use the circulator pump on the return without an internal check valve.

I understand your points about valves...the more the better when it comes to servicing at a later date.

I got the recommended size of the expansion tank from the manufacturers website but the chart was based upon what type of heating system and BTU boiler load...not water volume. I will have to do more research on the tank specs.

I will get the backflow preventer. Do you recommend treating the boiler water for a domestic system?

Is an automatic air vent required on top of the air scoop and on top of the actual boiler...or just on the air scoop?

I will also need a temperature gauge for the bypass piping in order to adjust the system water temp, correct?

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