Needing help with converting domestic hot water in my oil furance to electric

alansupra94

hi heatinghelp.com

Looking for some advice on what I should do in this situation.

I have a combination oil furnace that heats up my home (hydroponics) and has a domestic hot water.

I plan to keep the oil furance heating section for now but want to stop using the domestic hot water section as I am moving to an electric boiler that runs off my solar energy.

Here is what the original water piping layout looks like


Here is the proposed layout


Proposed is definitely not set in stone and was done this way for a couple reasons (that may not be correct or can be changed).

1. I am not sure if that section for domestic water can be removed.
2. If it can't be removed, I assume there must be water inside of it to protect it from overheating air? (unless that doesn't matter).

Thanks

alansupra94

So it seems after researching a bit more this might be the correct way to do it:



As for the controls, I am going to replace it with a different aquastat that is for heating only. No need for a minimum temperature anymore. Just the basic controls for firing on when there is a call for heat.

HVACNUT

Glad you're getting rid of that particular setup. Blasting 180° water into a plastic condensate pump isn't a great idea. The location is a PITA for a tech to work on the pump and filter too.
A check valve on the return is a no no. The whole thing has needed TLC for a long time.
What's the solar array look like? It's enough to power an electric boiler continuously?

WMno57

Domestic hot water systems on city water should have an expansion tank to accommodate the expansion of water when heated.
You are on a well. If your well system has a pressure tank, this existing tank will accommodate the expansion of the heated domestic water. No check valves or pumps needed, other than the well pump.
The Hydronic space heating system (oil boiler) should be connected to the domestic water system with a pressure reducing valve, and ideally upstream from the PRV, an isolation valve. The hydronic heating system operates at a lower pressure than the domestic water system.
Tell us more about your new space heating system, and new water heater.

Jamie Hall

I'll echo @HVACNUT 's last comment: is your solar array big enough to power a domestic water heater? Typically they take 4500 watts to run, at 240 volts, and that translates to a BIG array.

alansupra94

HVACNUT said:

Glad you're getting rid of that particular setup. Blasting 180° water into a plastic condensate pump isn't a great idea. The location is a PITA for a tech to work on the pump and filter too.
A check valve on the return is a no no. The whole thing has needed TLC for a long time.
What's the solar array look like? It's enough to power an electric boiler continuously?

The condensate pump was there to just catch this weird small leak that was occurring on a pipe not associated with the system (it is for a spigot outside). It just happens to sit there.

Where are you seeing a check valve? Those are just directional arrows to show the flow of water. I don't think code requires a check valve for domestic water (it does for the hydroponic system which is seperate piping and not shown here).

WMno57 said:

Domestic hot water systems on city water should have an expansion tank to accommodate the expansion of water when heated.
You are on a well. If your well system has a pressure tank, this existing tank will accommodate the expansion of the heated domestic water. No check valves or pumps needed, other than the well pump.
The Hydronic space heating system (oil boiler) should be connected to the domestic water system with a pressure reducing valve, and ideally upstream from the PRV, an isolation valve. The hydronic heating system operates at a lower pressure than the domestic water system.
Tell us more about your new space heating system, and new water heater.

There is an expansion tank inside of the hydroponics loop after heating. I don't have any pumps besides the Taco circulator pump (in the hydroponics loop) and check valve (for not allowing hydroponic heating water backwards into the domestic hot water).

The heating in the house currently is baseboard heating with the basement having its pipes (for heating) running through the foundation. I have had a couple instances where the pipes in the foundation have frozen so now I run an automation (in a software called home assistant) that automatically sets the thermostat to different temperatures to call for heat and avoid the issue.

The plan however is to switch to mini splits in the basements (that do heating and cooling) and switch the central air (which only cools upstairs) to a heat pump to do away with heating oil. I plan to just keep the oil furance as a back up.

Jamie Hall said:

I'll echo @HVACNUT 's last comment: is your solar array big enough to power a domestic water heater? Typically they take 4500 watts to run, at 240 volts, and that translates to a BIG array.

Most standard water heaters don't pull 4500W continuously to heat water however that isn't an issue in my case for a few different reasons.

1. My water heater runs a special MPPT water heater setup that uses 3 300W solar panels to power the bottom heating element by itself.
2. The top element is still connected to the grid but in NJ we have "net metering" that allows for you to pay $0 as long as you don't go over how much energy you product monthly.
3. I have currently 10kW solar setup (2 sunnyboy inverters and 10k in Trina panels) with room to expand out to 18kW if needed. Bulk of my energy cost after monitoring has been A/C in the summer and multiple coral reef tanks I have (I have since sold off 4 of them and only have 1 that I installed into my basement dividing room wall). The system is grid-tied for simplicity right now and due to net-metering.

Derheatmeister

Depending on your solar exposure,proposed tilt,angle and a couple other factures it may be more economical to install a solar thermal DHW system vs. trying to heat the water with a VERY Large PV system.Someone with a Pathfinder and a program like T-sol can shed some light on this.
BTW ; hydroponics is for Plants..Hydronics is for heat

alansupra94

Derheatmeister said:

Depending on your solar exposure,proposed tilt,angle and a couple other factures it may be more economical to install a solar thermal DHW system vs. trying to heat the water with a VERY Large PV system.Someone with a Pathfinder and a program like T-sol can shed some light on this.
BTW ; hydroponics is for Plants..Hydronics is for heat

Lol I always mix that up. I also have a hydroponics setup for growing vegtables.

I did the calculations and cost-break down and it was way more expensive for me to do a DHW. They are definitely fantastic. I however, got most of my equipment from a friend that deals with surplus equipment so the inverters and panels were extremely cheap.

I found the hybrid MPPT setup should work pretty well for most of my needs. It has dedicated solar panels for the lower element (that directly heat the water). The upper element is grid connected and only heats when the lower element isn't producing enough. That energy would be offset with net-meter government program in NJ as well.

My main purpose was to reduce the overall cost of electricity and heat oil without spending a huge amount on equipment. Even if I still pay an electric bill, if it reduces it by 50% it would be a big win for me.

Thanks to everyone that has commented so far.

Hot_water_fan

1. My water heater runs a special MPPT water heater setup that uses 3 300W solar panels to power the bottom heating element by itself.

That’s cool! Obviously with net metering, all of this concern is for naught, but I like the concept. With how cheap Solar PV is AND since you can use the output for more than DHW, solar thermal has essentially died out in the US. Probably <1% of the market. 

WMno57

alansupra94 said:

1. I am not sure if that section for domestic water can be removed.
2. If it can't be removed, I assume there must be water inside of it to protect it from overheating air?

I think what you want to do is called abandoning the coil for DHW (domestic hot water) in the boiler. Yes, it would probably be better to leave the coil in place (abandon) than try to remove it from the boiler. I think it would be better full of air with at least one end open. Because it is a water to water heat exchanger. The coil is not exposed to the fire side of the boiler.

alansupra94 said:

There is an expansion tank inside of the hydroponics loop after heating. I don't have any pumps besides the Taco circulator pump (in the hydroponics loop) and check valve (for not allowing hydroponic heating water backwards into the domestic hot water).

There should be two separate cold water supplies to your boiler. One for hydronic space heating with a PRV, and the other for the domestic coil. No check valve, other than what might be built into the PRV.

alansupra94

Hot_water_fan said:

1. My water heater runs a special MPPT water heater setup that uses 3 300W solar panels to power the bottom heating element by itself.

That’s cool! Obviously with net metering, all of this concern is for naught, but I like the concept. With how cheap Solar PV is AND since you can use the output for more than DHW, solar thermal has essentially died out in the US. Probably <1% of the market. 

It is funny because locally I know at least 3 homes in NJ that have DHW but are much older systems. Seem to work great though.

alansupra94

WMno57 said:

alansupra94 said:

1. I am not sure if that section for domestic water can be removed.
2. If it can't be removed, I assume there must be water inside of it to protect it from overheating air?

I think what you want to do is called abandoning the coil for DHW (domestic hot water) in the boiler. Yes, it would probably be better to leave the coil in place (abandon) than try to remove it from the boiler. I think it would be better full of air with at least one end open. Because it is a water to water heat exchanger. The coil is not exposed to the fire side of the boiler.

alansupra94 said:

There is an expansion tank inside of the hydroponics loop after heating. I don't have any pumps besides the Taco circulator pump (in the hydroponics loop) and check valve (for not allowing hydroponic heating water backwards into the domestic hot water).

There should be two separate cold water supplies to your boiler. One for hydronic space heating with a PRV, and the other for the domestic coil. No check valve, other than what might be built into the PRV.

Water supply comes in from one pipe and splits off. One split goes to domestic hot water. Other goes to a PRV with a backflow preventer.

Hot_water_fan

It is funny because locally I know at least 3 homes in NJ that have DHW but are much older systems. Seem to work great though.

Oh they can work! That’s never been the issue.