hot water plenum loop in forced air furnace

M68

I have radiant heat in my basement slab that runs off an 11KW electirc boiler on a slab stat.  I also have a 100,000 BTU forced air PROPANE furnace that does most of my upper floor heating, or the whole house if they shut my boiler down for a time because I am on a ripple contract from the electric company, I am looking for an opinion on how sensible it would be to install a hot water coil loop in my forced air furnace plenum that would run off of my nearby electric boiler.  I would like to drastically drop my propane use because I am at an average of $2.20 a gallon (I use about 300 gallons per winter).  I enjoy a 35% discount on electric due to the ripple contract. I realize I'd have to have about 135 degrees in the plenum to be effective.  I run my floor at about 70 degrees and it does little good to crank it up because it is not effective upstairs.  I got one bid for about $1500 for the loop work, but I am more concerned about effectiveness than the price.

Thanks for the advice/comments  

Brad White

When you say "loop"

do you mean a circuit to a proper coil in the ductwork? Or coiling pex inside the plenum? I presume and endorse the former. A properly selected coil for low temperature hot water might well be four rows, two at least, maybe three, but four rows will give the most flexibility at low temperatures.



The effectiveness is all in the coil. These are made for proper transfer of heat between hot water and air.



We cannot and will not discuss price here, one of the few rules, I hope you understand.

Xray

Hot water forced air

This is actually a fairly common application.  You will need a properly-sized coil with 140* water run through it. Proper control setup and sheet metal work demands a reputable contractor. 

EricAune

Electric Plenum Heater

Have you checked into electric plenum heaters? Thermolec, Electro Industries and (I'm sure) a host of other manufacturers make modulating electric plenum heaters for this very application.  You would still get the low rates through the "off peak" program and save on the cost of the piping and controls.  This, of course, would require additional room allowed from the electric service panel, just a thought.