T-stat wiring so OWB runs the fan on my lp gas furnace while allowing me to use gas as a backup.

MGOBLUEGUY

What is the simplest, no hassle way for me to use my boiler for main source of heat and the lp gas as secondary? I really don’t want the fan to run constantly while the boiler stat calls for heat and the gas stat is working at a lower set point.

MGOBLUEGUY

This is a gas forced air furnace/ Outdoor Wood Boiler setup.

lchmb

put an aquastat on the coil to activate the blower.. when the coil is above say 150 have the blower come on... when it cools down it shuts the blower off and Tstat takes over for gas... just a thought

ratio

Hydro coil on top of the LP furnace? Baseboards? A two stage heating thermostat, with the 1st stage wired to the OWB and 2nd to the LP furnace, would be a start; if you need to bring on the fan during the OWB heat set the thermostat up as electric heat, then it'll call for fan when it calls for heat. Check the fan-only speed tap to make sure you're moving enough air.

You will probably need an interposing relay in the mix, a RIB relay is a quick & easy one to use.

DZoro

Or 2 stats one set to turn blower on, the other for the gas furnace.

MGOBLUEGUY

Yes, Lp gas furnace has a heat exchanger (water to air). All I need is blower running upon call for heat. I could use an aqua stat on the coil, but I’d have to use it as a low temperature cutoff to prevent the blower from running constantly if the fire goes out on my OWB. It would need to be fed via a parallel tap on the existing circuit, controlled by a second t-stat. That’s pretty invasive, but doable. Just rather not go there if I don’t have to. The simple two-stat method is doable, however, whenever the boiler fire gets low or goes out the blower will run constantly until someone either changes the t-stat settings or restarts the fire. That’s fine for emergency backup, but I’m looking for automatic control. I’ve wondered about a two stage stat but other forums have said they would not be a viable option, something about the reversing valve on a geothermal system or something. ??? What would the RIB relay be used to control? If it’s so the blower doesn’t run constantly in the second stage wouldn’t we still need something else?

ratio

Well, you would run into a problem if you installed a heap pump thermostat, but just a regular 2 heat 1 (or 2) cool stat, with the fan set to electric heat will do exactly what you want. You'll need a relay on the OWB to isolate the power (W1 trips the relay, the relay trips the OWB) but after that the only down side is that the thermostat will energize the fan during any heat call. Usually the heating equipment controls the fan itself, allowing it to keep the fan off until the HX is warmed so you don't blow cool airthe first minute or so of operation.

Another idea, slightly more work but operation will be closer to what you probably have now is to add an aquastat on the inlet to the heating coil set to slightly below your running water temp & have that call for the fan (instead of the thermostat) during OWB heating operation. Still need the relay between the thermostat and the OWB.

A third option would be to monitor the OWB temp & pass the heat call to the OWB if it's at temp or the LP furnace if not. Still need a relay between the stat & the OWB, also need one of the fan control schemes to be implemented; and you'd loose the ability to stage up if the OWB can't keep up even though it's firing. This actually might be the most desirable if the OWB can carry the load as there won't be any temp droop (the differential between stage 1 & stage 2 heat calls).

Personally, I'd do the 2 stage stat with aquastat fan control; or fall back to the stat-controlled fan to save a few bucks.

EYoder

We do the third option using a Ranco temp control breaking the LP when OWB is up to temp. Or the two thermostat method. Either way may take an additional relay or so depending on existing wiring. But relays are cheap.