Tankless heater as a heat source

[James Glenn]

I have a 4.5 GPM tankless water heater supporting a hydronic heating system in my garage. Right now I have a Watts 500800 recirculating pump on the hot water side right after the Taco air scoop and pressure relief tank. The water runs through the pump and up to a blower (radiator) and back down to a 12 section cast iron radiator. I have to adjust the pressure on the water heater temperature control down to almost nothing to get it to fire. The system has 55 PSI and is plumbed with thick wall copper piping (except at the connections to the air scoop and the radiator (there I used galvanized fittings with dielectric couplers). I'm running a 50/50 mix of RV antifreeze in a closed system. So, I was told that I needed to get the pressure up on the cold side intake with a Taco 007-F5-7IFC Pump. If I remove the Watts pump on the hot side and put the Taco on the cold side will that do the trick? I'm close to balancing the temperature right now in cold weather running (e.g., with the gas adjusted to the lowest setting, the system produces just slightly more heat (slowly inches up to the 168 degree cutoff). The system produces the best heat at 150-160 degrees. Due to the low pressure from the Watts pump, I had to move the temp pressure switch to the outside of the box so I could turn it on with the cover on. If I put the Taco inline on the cold side, will the heater function more or less as designed? Also, will the Taco increase the GPM movement and give me the heat reduction on the hot side I need to reach a balance? Will it give me enough pressure to put the switch back inside and have the unit thermostat function normally? It's my first attempt at this. It works, but I'd like to get it set up right.

 

[Fitter30]

Pump doesn't care where it is in the system because it's circulating the water. I would want the pump before the heat with air separator and expansion tank on the suction side of pump. The rv antifreeze is it premix 50/50 or did you dilute it. RV antifreeze doesnt have corrosion inhibitors in it.https://www.supplyhouse.com/Nu-Calgon-4188-07-Freez-Kontrl-Glycol-1-Gallon. 40% -20* burst protection. The more concentration of antifreeze the harder it is to pump. Couldn't find a pump curve with antifreeze for the taco pump. Don't think your pumping the 4.5 gpm with the antifreeze . System pressure with pump off 12#. Like to see some pics of the system and a diagram the piping. That watts pump might not be big enough also.

 

[Sponsor]

 

[James Glenn]

Pump doesn't care where it is in the system because it's circulating the water. I would want the pump before the heat with air separator and expansion tank on the suction side of pump. The rv antifreeze is it premix 50/50 or did you dilute it. RV antifreeze doesnt have corrosion inhibitors in it.https://www.supplyhouse.com/Nu-Calgon-4188-07-Freez-Kontrl-Glycol-1-Gallon. 40% -20* burst protection. The more concentration of antifreeze the harder it is to pump. Couldn't find a pump curve with antifreeze for the taco pump. Don't think your pumping the 4.5 gpm with the antifreeze . System pressure with pump off 12#. Like to see some pics of the system and a diagram the piping. That watts pump might not be big enough also.

Thanks for the info. I'll get some pictures uploaded tonight.

 

[James Glenn]

Thanks for the info. I'll get some pictures uploaded tonight.

 

[Fitter30]

Use a taco 008 pump has a higher head than a 007 and with the antifreeze you will need it. System pressure can be lowered to 12# and expansion tank bladder pressure set at 12# when system is cold use a bicycle pump or be very careful with a air compressor. Air bleed at fan coil would make getting the air out easier and a valve on the oulet on pump for service.

 

[James Glenn]

Sorry for the long gap in reply. I'm going to move the pump location and use the 008 in place of the Watts 500800. I'll put the expansion tank and the air scoop on the suction side of the cold water return. I added another 15 fin cast iron radiator and that seems to balance things well. Do you see any safety issues with this setup? The settings on the THWH are at the lowest gas setting and the lowest heat setting but still delivers heat in the garage up to 60-65 degrees when the outside temp is in the 30s.