This article explains one way that you can configure a hybrid heating system for your house in a Schumeresque environment, but it is also potentially a way to cut your heating bills before TSHTF, depending on the prices of various heating fuels in your area.
We live in North Idaho, in a house that would be better suited in Hawaii. It’s watertight but mostly a heat sieve. Each of the last few years as the propane prices jumped each winter, we ended up getting hit with astronomical bills to keep the inside of our rather large home livable in outdoor temps that, for months, hovered between 20 °F and –10 °F. We use the wood stove that was already upstairs when we bought the place, and we have added some house insulation, installed double pane windows, and done all the usual maneuvers to limit heat loss, but the basic structure of most of the house is still about R-3 and right now we don’t have the money needed to get it all up to snuff. We have a forced air propane-fired furnace, but in our region wood pellets are much cheaper than propane and that was the basic reason that I started thinking about how to take advantage of that fact.
I came up with an interesting approach to marry the existing propane furnace system to a recently purchased, used pellet stove. Normally, pellet stoves provide lots of heat in a limited area, at a relatively low cost per BTU. Their drawback is that, typically, you can’t get that cheap heat spread all over the house so you end up with one nice warm region, and many cooler regions in other rooms or on other floors. Turning on the furnace blower can help to move the warm air around somewhat, but airflow patterns and the tendency for heat to rise often thwart this approach significantly. Then there is the fact that the two systems don’t “talk” to each other so you could end up with the furnace blower running when the pellet stove is cold, or it’s off when the stove is cranking out the heat, and manual synchronization requires constant attention.
I put the pellet stove in the same room that has the furnace closet and cold air intake (aka the cold air return). I placed it on an outside wall of the house and plumbed the flue through an existing small window, re-framing half the glass and using a wall thimble to separate the hot pipe from anything remotely combustible. I would have just gone through the wall but in our walkout basement it is cinder blocks filled with puffed mica and I did not want the mess, or the reduction in structural integrity. The stove’s hot air outlet in front is aimed, more or less, at the cold air intake of the furnace. Make sure that you install both a smoke detector (if you don’t already have one near the furnace) and a carbon monoxide detector in the room. Consider having the stove flue professionally installed if you aren’t certain that you can do it in a way that gives you a safe and decent looking result.
Instead of putting a thermostat on the pellet stove, I installed a 7-day multi-cycle programmable timer that provides thermostat-like contact closure at the times I programmed. This does two things. It helps to avoid too much repeated use of the self-igniting feature of the stove – often the first part to go bad and a costly part at that. Secondly, it assures that in the winter, the heat comes on long before we are awake so the house is fully warmed when my wife gets up. This part is very important because If Momma Ain’t Happy, Ain’t Nobody Happy (IMAHANH). James, you might want to add that to your glossary. [JWR Adds: Done!]
The timer starts the pellet stove and heats that room quickly. In a normal system this would soon tell the furnace thermostat that the house is warm enough and no action is required, but I want the blower to operate to spread the heat using the existing ducts throughout the house. So I installed a second mercury-switch type thermostat and placed it so that it could “feel” both the heat in the room from the pellet stove and the cooler air returning from the balance of the house when the furnace blower is on. Here’s the part that seems backwards – but it works perfectly. I used the “air conditioning” side of the thermostat and tied the switch in parallel to the furnace blower’s manual fan terminals. These are the wires that go closed circuit when you flick the house thermostat’s blower switch from “auto” to “manual.” Now I have two devices that can turn on the furnace blower and they operate independently without interference. I leave the house thermostat’s blower switch on “auto” so that it works with the furnace in those rare times that heat is required but my pellet stove is not on. But when my pellet stove heats the room, the new thermostat thinks that the room is too hot (above ~76F in my case) and it “turns on the air conditioning” which is actually my furnace blower. Voila ! My house furnace is spreading the heat from my pellet stove. When the timer tells the pellet stove to shut down – like as bedtime approaches – the utility room starts to cool down, aided by the cooler air returning from the rest of the house. When the room gets below the “air conditioning” setting the thermostat shuts off the furnace blower. If, during the night the house goes below the temperature I have set for the original furnace, it can come on and do its thing as before, but I set that nighttime temp quite low since we are sleeping in warm beds anyway.
Using this scheme, my propane bills have already dropped to around 25% of what they were and even with the cost of the pellets, my total heating costs are way down!
Yes, you need electricity to run the pellet stove timer, the pellet stove and house furnace blower, but in a TEOTWAWKI scenario I’ll be using my diesel generator to keep the food freezers and critical accessories “refreshed” anyway. The thrifty aspect is that the pellet stove’s timer has an internal rechargeable battery backup that it uses when turned off, so none of the parts of my new system produces “phantom loads” on my electrical network. I intentionally used a [traditional bi-metal style] mercury switch thermostat ($2 used, from Habitat for Humanity) because it has better hysteresis characteristics than newer solid state battery operated thermostats. A thermostat that controls a furnace is either off or on, with nothing in between. The thermostat is a system; the input is the temperature, and the output is the furnace state. If one wishes to maintain a temperature of 71 °F, a solid state thermostat will try to stay as close to that temperature as possible, often cycling the furnace and blower on and off many times per hour. This is both inefficient and hard on the furnace parts. Some mercury-switch units allow you to set the “width” of the hysteresis. So you could, for instance have the furnace go on when the temperature drops below 68 °F, and turn it off when the temperature exceeds 74 °F. This thermostat exhibits hysteresis. It keeps the added thermostat from cycling a lot after the pellet stove is off but the room is still warm enough that stopping the blower (and the flow of cooler air into the room) would result in the thermostat thinking it needs to” turn on the air conditioning” again and again.
All my best to you, James, and your family in this difficult time. Keep your powder dry and your Bible open – Ted