Efficiency in heating is a somewhat complicated subject.

When you say "efficiency" are you talking in terms of money spent for that heat?

OR

Are you talking about "waste" that goes up the flue when you run the furnace?

Electric heat is 100% energy efficient: 1 btu in = 1 btu out. However, in many parts of the world you pay more for electric than natural gas. (propane typically costs more and often on par with electric costs --- but electric costs can vary too.)

I know AC is the least of your concerns for your climate... but does this house have AC?

In a 2-story zone it is always best to zone the first and second floors. Most of the time this is done with one furnace and dampers in the duct work. The better way of doing it is have two furnaces and AC condensers which can independently heat and cool each floor.

I am fortunate that the original owner of my house upgraded to two furnaces and AC condensers. I believe my heating and cooling bills are lower and my house is more comfortable than my neighbors which only have one furnace. The two furnaces will allow you to set back the temperature of the first floor when you sleeping in the upstairs bedrooms, and set back the upper floor during the day when everyone is on the first floor. This will save heating costs. You will also have more even temperatures on the two floors. You should not have to over heat or over cool one floor, so the other floor is at the temperature you want. This is also a potential energy savings.

Having two furnace is actually a added selling feature of this house. This assumes the furnaces were properly sized and installed. The only drawback is someday having to replace two furnaces instead of one. Make sure during the inspection the furnaces are both operating properly and in good condition.

Two furnaces won't be any more efficient but it will improve heat distribution and comfort. It's definitely a plus.

Hi, Taylor-Marie,

With respect to zoning of HVAC systems, zoning enables you to set and control to different conditions in different areas of your home. Zoning may consist of a system of thermostatically-controlled dampers and a single air handler or separate units for each floor of a home or multiple air handlers or even a combination (sub-zoning each level.) Based on your description, the home is zoned by floor with a separate air handler for each.

If the air handlers are in the conditioned living space, then the combined efficiency of two units versus a single unit should be pretty close to the efficiency of a single unit. You just trade off the additional upfront and maintenance cost for the flexibility and comfort. In a climate zone like yours, having two units also mitigates the risk of having your furnace fail when needed most--you'll at least have heating on one level and should be able to avoid pipes freezing.

Hi everyone! Thank you for the replies! I guess efficiency isn’t really what I’m concerned with - cost is. Natural gas isn’t cheap here and so I’m really asking more so, will two furnaces be more expensive to run on the day to day then one would be?

@Austin Air Companie, I’m concerned with cost - I shouldn’t have put efficiency in hindsight. Also no, the house does not currently have A/C so that’s another thing to consider as we’d have to do two AC units I’d assume.

EDIT: I shouldn’t have said efficiency in my original post when I’m really concerned about cost of two furnaces on the day to day versus one furnace.

@Taylor-Marie Beck,

If you run two units at the same temperature set point as you would a single unit, your total heating load is the same and gas consumption should be, too.

Zoning by floors allows you to set different conditions on each and minimize energy use on a floor that is unoccupied. The greater concern, from a cost standpoint, is the incremental cost to purchase and maintain two units versus a single unit.

If you have two separate systems, you have the option to add air conditioning capability to either or both.

Assuming hypothetically just for the conversation that you have two furnaces that are each one-half the size of what a one furnace approach would require (and what it actually is doesn't matter), you should be much better off having two. With two separate sets of equipment, you can primarily heat where you are and not where you're not,. As an example, a higher setting downstairs and lower (or even off) upstairs during the daytime. Hot air rises anyway so assuming your stairways are not closed behind doors, having the downstairs on will provide some heat to the upstairs all the same.

What you have is preferable, think of it as a plus. Charles Ross Homes always has balanced, informed comments and mike_home speaks from experience, his comment above should be most useful for you to understand.

Elmer makes a good point which I neglected to mention. When the furnace on the first floor is operating some of the heat rises to the second floor. That produces less wasted heat. Even if you set both thermostats to the same temperature, you will find the second floor furnace to run less often due to some of the warmth coming from the second floor.

The other advantage I should mention is you always have a back up furnace. In the event one of the furnaces fails, you are not at the mercy of having an HVAC company come in on an emergency call. The one furnace will keep the house comfortable as you wait for the repair to be made.

@Austin Air Companie, I’m concerned with cost - I shouldn’t have put efficiency in hindsight. Also no, the house does not currently have A/C so that’s another thing to consider as we’d have to do two AC units I’d assume.

Ok, cost and efficiency go hand in hand so to speak. A more energy efficient furnace will save you money... because it is better at "reducing waste" --- waste is the heat in the flue that is expelled outdoors.

What kind of furnaces does the house have? Is the flue of these furnaces metal? OR is the flue of these furnaces "PVC"?

The flue is tubing that is connected to the furnace(s) and run to the outdoors in some fashion. How old is the house? How old are the furnaces? Get the Model # and Serial # of the furnaces if you can.

Really old standing pilot furnace, typically 60/40 very costly to run because anywhere from 30 -40% of the heat generated went right up the flue.

Newer furnace like 90's or so and later (metal flue) 80/20 --- 20% of heat produced goes up the flue. No standing pilot, electronic ignition & inducer draft motor, are typically good identifiers.

Even newer high efficiency furnaces (PVC flue) could be anywhere from 90-97% efficient. These cost money. You can't use metal flue venting all of that has to be converted to PVC. Done wrong and you'll have one heck of a mess. But by picking 97% efficient or some sort of "modulating" gas furnace wouldn't be that bad of an investment for your climate.

Given your climate natural gas is typically the cheaper option all things considered. What is your electric rates there? As in how many cents per KWH?

To convert to electric strip heat would be costly because you'd have to run new electrical to power those electric furnaces. You could pair those with heat pumps, but your climate would be a challenge for the heat pump option, IMO. Not that it can't be done... typically cost per BTU is much cheaper when it comes to natural gas. Going the heat pump option I would choose Inverter... which again is more costly. But if you want heat when you need it -- that's what you should do. The advantage in the heat pump is then you also have AC in the summer.

A heat pump will typically reduce the electric strip heat consumption around 50% depending on a wide variety of factors. (time in defrost, how cold it is, how cold it stays over long periods, how warm you like it inside, etc.) Inverter will reduce that further because it can produce heat at much lower OAT than traditional on or off heat pump -- two stage heat pump included.

Is having two furnaces usually more efficient and cheaper then having one furnace running all the time?

Two furnaces or not two furnaces: that is the question (with apologies to Shakespeare.)