What the previous owners did was install the best of both heating systems so that as the price of oil vs electric fluctuated they could benifit from using the cheaper of the two fuels. You will need to know the price of each to determing what you should be using year to year. Below a certian temp the oil will take over regardless of expense. That cutoff point depends on the make an model of the heat pump installed and where its efficiency curves lay.

Post some of this information back here and there are several folks that can help you determine the best settings for you.

My guess would be that the Oil heat is for Emergency or Aux. heating purposes. Most heatpumps, especially the older models, don't work very well below 40 degrees, aren't cost effective because it's hard for the heatpump to "catchup", or to keep your home at the setpoint temperature inside your home . I would assume that once the outside temperature drops below 40 degrees it automatically turns on the oil heat to compensate for what the heatpump may not be able to do on it's own - keep the inside temp at it's setpoint, with the thermostat satisfied. The "Heat" setting on the upstairs thermostat is probably for the heatpump operation, with the oil heat coming on when needed, via the outdoor temp. sensor which is set at 40 degrees. The "Aux Heat" setting on the thermostat is probably for the oil heat operation and is probably a manual over-ride of the heatpump, for use during such times as - it gets real cold and stays cold, or if your heatpump breaks down for some reason, you can still use the oil heat to keep you warn. It all depends on how the thermostat is wired, but this would be my guess.

I think they did figure that 40 degrees was where the efficiencies curves switched over. I found some graphs where they had calculated this based on the two units. I guess as the first post suggests that may have changed since our electric prices went up 70% this year thanks to MD's screw-up with regulation/deregulation.

My question was more related to the thermosat and the last post helps with that. I guess we really need to keep an eye on the heat pump and furnace and which is going based on the outdoor temperature and the thermostat settings. A little trial and error if things don't appear to be cutting in and out as they appear to be set up to do at 40 degrees. Right now we've only had a few hours a couple mornings that cold.

Thanks-

I thought heat pumps worked ok til below -6 deg C which is, obviously, below 32 deg F....but I believe bad things can happen if you attempt to use heat pumps below the minimum temp. I guess it's worth noting you should keep the outside unit - compressor or what have you - uncovered, and free from snow and ice.

It might be worth contacting the original installers to give you a lesson in it all, sounds like you scored some nice goodies :)

Kurtg,

We had similar set-up in my last home in Gaithersburg. We had a Lennox 5 ton Heat pump and a Thermopride Oil Furnace. Usually the controls (typically refered to as fossil fuel controllers) may have various options like outdoor temp sensors to automagically switch over from heat-pump operation to the oil burner. It sounds like this is what you have on your system. In such a case you can leave the thermostat on heat and the controls will engage either the heat-pump (when its over 40 degress in your case) or the oil burner when the temps fall below 40 and possibly when the heat-pump is in defrost cycle. If you wind-up with a period of sustained very cold temps its easy to just move the thermostat to AUX and you would only be running the oil furnace. Its a great system since during the shoulder seasons (spring and fall) the heat-pump is very efficient. Most of the time in the winter I simply selected AUX for the oil furnace and lock-out the hp since temps would reach the 40's during the day and most evening/nighttime temps would drop back into the 20's/30's. (late Dec/Jan/Feb)

Bob

Mine also has the "dual fuel" controls. I have gas furnace. I let mine work automatically. If daytime reaches 40 deg, the heat pump is cheaper to operate than the oil furnace. Saves a little each day in the cold weather and a lot on the many days when the temp is always above my switch-over setting.

I'm buying a home in MD which has Oil heating. I want to install a heat pump system and get the efficency that you've talked about. How hard would it be to add a heat pump to an existing oil only system?

eagle2sky,

Hard to say. Do you already have central AC? If so you may be able to utilize the existing air-handler. Your outside unit (std condensing unit for A/C) will need to be replaced with the new air-to-air hp and you'll need a new A-coil and lineset. Then you'll need to add on some controls, either via a fossil-fuel kit or a smart thermostat etc.

Bob

With the cost of electricity doubling over many parts of the country, I would be very careful before plunking down money for a heatpump.It may NOT be cost effective. You would have to do the math first.

I have bought a trane xl20i heat pump with the xv 80 air handler I am running duel fuel with oil. I live in reston va, and want to know at what temperature the oil heat will kick on? It 32 degrees right now and it has not kicked on, any suggestions on this would be appreciated. Also how do I know oil heat is working opposed to electric?

For the Op living near Annapolis. Academy Grad here, now living in Rockville.

I have a three year old Carrier Heat pump and a three year old oil burner.

Based on my research on my unit's effciency or performance versus outside temp and considering oil and electric costs, I have the cross over set temperature now at 25 degrees outside temp. (Started at 35 degrees, last year changed it to 30 degrees and now set to 25 degrees.).

You said, "...electric prices went up 70% this year thanks to MD's screw-up with regulation/deregulation." Not sure what this is about, I get my power from PEPCO and we have not seen a 70% increase in rates due to anything - and certainly not due to a "screw-up" by the State or anyone else. (My County has continued to add additional taxes to my oil costs, however.)

Your agenda may be showing. lol

I just paid $4.39 per gallon for 68.1 Gallons of heating oil... first delivery since December of 2012.

The temperature at which you would switch to the oil furnace is determined by a setting in the thermostat. What thermostat do you have? If can determine the model number you should be able to find the manual to figure out how the temperature is set.

You should hear the oil burner firing when it is on. The outdoor unit should not be running at the same time.

joeplumb said, "With the cost of electricity doubling over many parts of the country, I would be very careful before plunking down money for a heatpump.It may NOT be cost effective. You would have to do the math first."

I have to question this logic. My annual total cost of electricity divided by my total cost for recent years has been:

2013 = 14.0478 (Cents/Kwh) to date
2012 = 13.7582 (Cents/Kwh)
2011 = 14.1361 (Cents/Kwh)
2008 = 14.7412 (Cents/Kwh)

Oil in 2008 was $3.95/Gal and this year was $4.39/Gal recently.

(I might add that in 1969 I was paying 12 Cents a Gallon. lol )

Older belt-drive oil furnaces with the indoor-coil set directly on top of the furnace with no 6" or greater transition, can have a lot of back pressure due to the large HT/EX being too close the indoor evap-drain pan.

That problem is made worse with larger tonnage heat pumps...

Airflow should be checked at the diffusers; make sure the blower blades & indoor coil are clean.

Here is a link that might be useful: Oil furnace airflow problems

Philip: this is an old thread. you should have started your own.

If your thermostat is relatively smart, your oil will only come on when the HP can't deliver enough heat to warm the house within a certain amount of time (like 15 minutes). The XL20 is efficient and is most likely perfectly capable of producing sufficient heat down below 32F, more like 28F or more.

The tstat will stay on HP and as long as the temperature rises in the time period it will not activate auxiliary heat. Doesn't matter what the outdoor temperature is.

Now, if you have an outdoor temp sensor connected to the tstat, you can set these temperatures yourself based on the cost of electricity over oil and/or your own comfort.

weedmeister,

Thanks. I just realized this is a seven-year-old thread that someone dusted off and contributed to total confusion -

!@#$%^