One Gas Boiler - One Electric

mark ransley

What is your electric cost, unless its maybe .07 cents kwh it wont pay. At .12 kwh its more then Ng for average midwest prices. Forget a boiler if its electric is cheaper space heaters will do the same thing for thousands less. Electricity is generated by fuels, so it costs more and over the long term always will cost more. To test your thought get space heaters before upgrading your electric and buying a boiler and compare costs. Research fuel costs costs, BTU comparison, and the efficiency of what you have now. Insulation will save you today, electric I would not think will save but cost more to heat.

Jim Peters

I have a single zone Burnham gas boiler with cast iron rads. It was installed 10 years ago and replaced an old oil gravity feed system. There's a Taco circulator pump (1/25 HP 3250 RPM). The system is working well, however I'd like to install a second boiler (electric) and tee into the system. I'm wondering when I do this can I install a second pump and should I be concerned if the second pump could push the water backwards through the first pump? Should I install some directional valves to prevent this from happening? Also could both boilers (and pumps) operate at the same time or would there a problem with pressure or flow?
Thanks

Bryan_16

pumps

I would install pumps with internal check valves. This eliminates flow going backward through the boilers. I would be careful trying to run both boilers at once, the electric boiler needs a certain minimum flow and you might not be able to maintain it with the oil boiler running.

Rich L.

2 boilers?

What do you hope to accomplish with the second boiler Jim?

Jim Peters

Hi Rich,

The second boiler would give me the option to run on electric vs gas or switch to whatever energy source is more cost effective. I guess it's like a hybrid! At the moment electicity cost in my area is still fairly low as compared to natural gas.

scrook_2

Primary-Secondary

Pipe both boilers primary-secondary into the existing radiation circuit(s)?

Is the differance in energy prices great enough to justify the initial outlay?

Jim Peters

Yes, I was planning to pipe (tee) into the system, but don't think the gas boiler pump could be used as it probably doesn't have enough flow. Did you mean the pump too? The electric unit requires a minimum of 6.8 GPM. I'll double check the gas one and see.

You have a good point about the additional cost. Probably $2000 if I do it myself. Only the future energy cost will tell if it's worth it!

Jim Peters

The gas boiler pump is a Taco 007-F5 (Flow Range: 0 – 23 GPM). I don't think there's any check valve.

Rich L.

Primary Secondary

Jim, if it were me I would go with a primary secondary arrangement with both boilers feeding the main loop through closely spaced t's. I would do it with 3 pumps. The thermostat would bring on the primary pump for the house loop and then the chosen heat source with it's associated pump as required to maintain the loop temp. This would assure adequate flow through the house as well as the chosen boiler, with properly sized pumps of course. Please note, not all details are drawn in the picture, just enough to hopefully get the point across.

Good luck, Rich L

Jim Peters

Rich,
Many thanks for your suggestion and drawing. I really appreciate you taking the time to draw it out. I visited my supplier and he agrees with you on the 3 pumps. He suggested that I use some relays to start the primary pump and then the second relay would fire up either the gas or the electric boiler. I would have a manual switch to select which boiler to run, however we are thinking about a method to fire both boilers at the same time. Each pump would have a check valve and I understand about the closely spaced T's. Did you have any suggestion about the make of a thermostat that would control the circ motor or were you thinking along the same lines and use relays?

Thanks again.

Rich L.

T'stat

You're very welcome Jim. I would think most any t'stat would work for you. You could pick a style you like. I've been using the Honeywell 511 and 611 series on a lot of my jobs lately and been very pleased with them. I would probably set it up to operate a pump relay to operate the primary pump as well as control the boiler and pump of your choosing. You could use a three way switch to manually choose between boilers.

Jim Peters

Hi Mark,
Very good points. I'd thought that I'd probably just go with the electric baseboards, but it's a bit hard to locate them around my big cast iron rads. They tend to be located right where the baseboard would go!
I'm located on the west coast of Canada and pay 0.05980 /kW.h and it steps up to 0.07210 after some usuage. The electricity is 100% hydro generated. Our Ng cost isn't so friendly.

Mark Custis

How about

Electric radiant panels?