Convert from old furnace to HWH

Old 08-07-16, 06:38 PM
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Convert from old furnace to HWH

I've been reading a bunch of threads but still cant find an answer. I have a really really old furnace that has the hot water coil I don't have the money to replace the whole furnace and I want to put in hot water heater instead. I have a lot of knowledge I can wire the panel and do the plumbing. I just don't know what to do with the coil at the furnace. any help will be appreciated. my first post wish me luck.
Old 08-07-16, 11:40 PM
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Simply re-route the supply (cold) and distribution (hot) water piping from the thankless coil to the new stand-alone heater. You don't have to do anything with the coil. You will want to reset the "low limit aquastat" on the boiler to its lowest setting. Some aquastats have the ability to disable the low limit completely.
Old 08-09-16, 05:30 AM
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You might need to experiment with the low limit aquastat setting. In summer you would now switch off the furnace completely and the aquastat setting then means nothing. In fall and spring, if the aquastat lower setting is too low, the heat may be slow in coming on as the boiler may need to come up to operating termperature again.

If you want to, you can leave the hot water coil in the picture and hook up the stand alone water heater after it. When the furnace is on, the coil will act as a preheater and lower the amount of work the stand alone water heater needs to do and it will also seem as if you don't run out of hot water as often.

I don't think that the inside of the boiler in summer would ever be lower than the incoming (cold) water temperature so leaving the boiler coil in the water path would never detract from performance.

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