Dual Boiler Set-up Feasibility?

GoulyONE

Hello all! I am a new member to this forum and I found it while searching for answers to my current question. I look forward to utilizing all the experience and knowledge in these in these forums as I work my way through my "money-pit".



First off, I don't know if I should be posting this here or in the plumbing section but here goes:



I currently have hot water baseboards supplied by an oil-fired boiler. The boiler itself is approximately 10 years old and seems to run well (no issues since installation). However, I just received my most recent oil bill and it disgusted me. My neighbor recently switched to gas and it saved him a ton of money so now I am considering installing a gas boiler. I already have gas in the house, it runs my hot water heater.



Considering that the oil boiler seems to be in good condition and that I recently invested in a new oil tank, I would like to keep that system in place as a "back-up". Can I plumb/wire the two systems such that I can switch between the two as need be (changes/swings in fuel prices), only operating one system at a time?



I have an engineering degree so, in theory/on paper (in my mind), I would think this is doable. I would think that, in simple terms, I could just set the system up such that I can bypass, via valving and switches, the plumbing and electrical circuits for the "back-up" system. However, I do not have any plumbing/electrical experience so that is why I am reaching out to you.



Keep in mind that although I do not intend to contract the work, I will not be doing this solo. I have a licensed electrician and licensed plumber in the family that I will be working alongside of. I'm sure they will both have their own opinions on the topic but I wanted to do my research before I approached them with my proposal.



My next question would be regarding my options for "laying-up" the back-up boiler for an indefinite amount of time, but that is for another topic and another day.



Sorry for the long winded explanation but I look forward to hearing your comments and advice.

heatpro02920

sure you can...

I have done this a bunch of times, using multiple boilers can be done a bunch of different ways but I prefer to do it with a primary loop...



The plumber in your family will sure know this method, simply make a loop and put your 2 boilers into it using closely spaced tees,{the loop will have a cric of its own and each boiler will have its own circ} wire the units and their circulators to only run when each unit is hot, so if the gas boiler is running, its designated circulator will run also there fore circulating its hot water through the loop, now when a zone calls it will also pull off of a loop with closely spaced tees....



Sorry if I am not explaining this perfectly, I can draw it better than speak it, and I can pipe it almost as well as I can draw it, lol...



Now the controlling can be done a bunch of ways also, I prefer using switching relays and aquastats with a single thermostat that will perform aux heating tasks, so in other words, your t-stat has a switch that lets you choose which boiler to run, then when that boiler runs the aquastat senses when it is hot and runs its designated circulator when any of the zones are calling.... With multiple zones this gets tricky, another way to do it is a single switch that powers which boiler you want to use, this is also nice incase you ever need both boilers at once... {in your case probably how I would do it}...



This all takes some pretty serious pipe fitter savvy, I have done it dozens of times, with outdoor wood and other solid fuel boiler, gas and oil, fuel and solar, ect...



This is just the way I would do it, I can think of 5 other ways, I like p/s method since it doesnt need any manual valve switching, sure anyone can just throw in some ball valves and pipe 2 boilers together, but what fun is that, lets make it look like it can fly or does something really important....



good luck, sounds like a fun project, enjoy it and since you are doing it your self, use all good stuff... there are some awesome valves and components out there, be sure to post pictures too...

webstone will have tons of stuff for your system..

http://www.pexsupply.com/Webstone-58744-0-1-Sweat-Run-x-1-Hydro-Core-Right-Flane-Manifold

http://www.pexsupply.com/Webstone-58654-1-1-4-x-1-Pro-Pal-Full-Port-Brass-Ball-Valve-w-Reversible-Handle-Primary-Secondary-Loop-Purge-Tee-600-WOG



you will only need 1 pressure reducing valve, expansion tank, pressure reducing valve, and back flo, but you will need a lot of circulators, at least 1 for your primary loop, 1 for each boiler, and then 1 for each loop of heat, I would use grundfos alphas for the boiler pumps and primary and taco bumble bees for each zone loop... You are probably talking around $2000 just in materials...

First thing to do is perform a heat loss on your building and pick a gas boiler, figure out all your pipe sizes, most likely a 1 1/4" primary and near boiler piping with 3/4" zone piping will be safe {just depends on your boilers and load}, I have done it with 1" and 3/4" just depends on your system, then draw it up and make a parts list..

heatpro02920

Dug this up

here is something similar we did, its a drawing I made for my techs when they were doing something like what you are thinking of, I think....





This is just a drawing I made for them to get the idea, you can move your pumps around, it doesn't show any check valves or all the purge stations and temp/psi gauges. I will check later on when I get home to see if I have a picture of this job finished, it came really nice, and has been working great, no customer complaints...



the low voltage to choose boilers is a simple spdt switch, you wouldn't run them all separate how I drew them {and how my guy did it first was a single wire like the drawing, which we replaced with an 18-3 from the switch to the exp control and then a pair of 18-2's to each boilers TT... Pretty simple, although you can not run both boilers with this switch, there are switches that allow both available though and you still only need 3 wires...

MikeG

Propane and electric

This is a timely thread.  I have started to explore the idea of installing an electric boiler as a dual heat source to my boiler.  A lot will depend on where the trend in propane is heading.  One heating season does not make a trend.  Right now with my current price per KWH assuming 100% and propane at 90% efficiency I cold save $10 per 1 million BTUs.  Not much but propane was higher earlier. I also know system efficiency is a part of the equation also.  I attached a page from the Munchkin install manual with some added notes on what my current system is.  If I was doing it now I would probably do it a bit different. Its a M80 boiler.  Installed in 2008. It is a pretty tight install in the mechanical room.  I've had no problems with it.  Back in January we had some -10 to -18 days with winds and more minus days than usual this season.  I do get some short cycling in the shoulder season. Maybe the electric boiler will help during this period.  I know I could add a boiler with close tees or a LLH.  I'm just try ing to get my head around the control strategy and the mechanics of doing it.  I'm not opposed to manual switching.  I know the question of ROI always comes in.   Is it worth the expense of the equipment and install to save a few bucks or just pay the propane.   Is the break even point reachable.  All I know is that back in January and some days in February I was going through 10 gals a day or about $40.  Granted not a lot of days like that.  My boiler ran almost non stop.  I did lose a bit on the temp but I think that was more of an issue of one under radiated area and some needed insulation.   Electric wold have been about $15 a day less.  It makes you think.   Just trying to get some ideas.  Thanks Mike

MikeG

Propane and Electric

I figured I should add the attachment

Charlie from wmass

what boiler do you now have?

you say yours is 10 years old. you may be able to just change to a gas burner instead of changing out the whole boiler. A photo of your current boiler would give us a better idea of the feasiblity of this.