Convert from tankless coil hot water to electric heat pump water heater

[Ken1999]

I currently have a 25 year old tankless coil oil boiler (Trianco Heatmaker) for my hydronic baseboard heating and domestic hot water(DHW). I would like to no longer use the oil boiler for my DHW needs and use an electric heat pump water heater instead. I am located in upstate NY. I don't need any heating for more than 6 months of the year so it is extremely wasteful (and expensive) to keep the tankless coil water hot all year round. I have two questions:

1) When I connect the heat pump water heater (which I know how to do) how do I safely disable the tankless coil for hot water? I will still need the boiler for my home heating needs in the winter months. Ideally I'd like to set up some kind of bypass so that I could use the coil again as a backup for DHW if needed, but if that's not a good idea I'm fine with disabling it completely.

2) What should I change my aquastat settings to for high/low limit (currently 180F/160F)? I am planning on shutting off the boiler for the summer months and restarting it again fall.

Thank you!

 

[John Gayewski]

I currently have a 25 year old tankless coil oil boiler (Trianco Heatmaker) for my hydronic baseboard heating and domestic hot water(DHW). I would like to no longer use the oil boiler for my DHW needs and use an electric heat pump water heater instead. I am located in upstate NY. I don't need any heating for more than 6 months of the year so it is extremely wasteful (and expensive) to keep the tankless coil water hot all year round. I have two questions:

1) When I connect the heat pump water heater (which I know how to do) how do I safely disable the tankless coil for hot water? I will still need the boiler for my home heating needs in the winter months. Ideally I'd like to set up some kind of bypass so that I could use the coil again as a backup for DHW if needed, but if that's not a good idea I'm fine with disabling it completely.

2) What should I change my aquastat settings to for high/low limit (currently 180F/160F)? I am planning on shutting off the boiler for the summer months and restarting it again fall.

Thank you!

It's not a good idea to keep stagnant warm water in your piping for six months and then use it. So there's that.

What's the thinking behind changing the aqua stat settings? If your not using the coil it should be cut.

 

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[Ken1999]

Thanks John. Makes sense. I don't really want to keep warm water in the coil either. Is my only option to just remove the coil altogether or can I just cut the input and outlet lines into the coil and remove any standing water inside? I don't plan on keeping this boiler for very much longer anyway.

Seems like I would just leave the aquastat settings alone then, and just cold start the boiler once a year in the fall.

I'm fairly new to plumbing and boiler DIY so any and all detail is appreciated.

 

[Reach4]

I wonder how it would work to run the supply to the tank WH thru the existing coil. Then have some valves. I am not a pro. Just a possibly deficient idea.

 

[Ken1999]

I wonder how it would work to run the supply to the tank WH thru the existing coil. Then have some valves. I am not a pro. Just a possibly deficient idea.

That's definitely an option. The only problem is my coil reduces the water pressure so much you can only have one hot water faucet on the house at the same time, but that might work as good backup option. I did come up with this setup below that's lets me run the tankless in series with the heat pump, or I can bypass the tankless coil and use the heat pump water heater exclusively. I would always leave a path to cold water open so that I have an expansion path to my expansion tank.

It's probably not worth the hassle to build something like this out though. If I really do need a backup I could just temporarily connect the tankless into the heat pump or directly to the house with some sharkbites.

 

[Jadnashua]

I had a NG version of that boiler for a few years, and it was more trouble than it was worth! It was replaced long ago.

You don't need to run the domestic hot water through that coil, but you could. In the summer, it wouldn't be stagnent, since it would be feeding your new WH. In the winter, unless you changed the settings (I don't remember that you can change the controls to not allow it to produce the domestic hot water, but maybe), it could preheat the water going into the new tank. Depending on your utility rates and oil costs, it's probably still cheaper to bypass the coil in the thing and rely on the new WH.

 

[John Gayewski]

You can cut the lines to the coil, blow the water out, put adapters on the pipe so that iyer can be used in the future if one needs to use it.

Your drawing will work as long as you can balance it so that your sure flow is coming though both. I think you'd need a flow meter of some kind to make sure you don't just have a dead leg of piping with no flow.

 

[Ken1999]

Thanks everyone for the responses. I will cut the lines to the coil and blow the water out. That seems to be the simplest and most cost effective option.