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Thread: Hybrid Oil

  1. #1
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    Hybrid Oil

    Newbie poster here....

    I live in N. Virginia (mild-ish winters, daytime highs typically in the 40s, 3-sigma is probably 25 to 55 degrees) and have a forced-air oil furnace that came with the house. The furnace was replaced by the former homeowner in 2003; she put in a mid-range system in preparation for selling the place. I'd like to convert the furnace to a hybrid system -- i.e., oil furnace with heat pump -- on the premise that our mild winters are better suited to heat pumps than furnaces, but the furnace is worth "hanging on to" for the occasional cold spell. Note: I'm a homeowner, not an HVAC expert, so please correct me where I go astray. I'd rather be told I'm wrong than find out after the system goes in.

    So I've started looking around for a hybrid-oil system. I've found lots of references to/comments about hybrid-oil systems, some of which are on manufacturers' web sites, but haven't found a single system. Plenty of hybrid-NG and hybrid-LP systems, but none with oil. Unfortunately, NG isn't an option in my area. And AFAICT, conversion to LP isn't cost effective, even at the current home heating-oil prices (currently $4.51/gal, although prices for next season have yet to be set).

    So, the actual question: Are there any hybrid-oil systems out there? Can anyone point me to any information/systems/solutions on any of these systems? I have a billion questions on this stuff, but want to do some homework rather than ask a bunch of questions that you folks have been through numerous times already.

    All info (and clue adjustments) appreciated.

    Cheers,
    Vince

  2. #2
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    A hybird/dual fuel system is any heat pump witha fossel fuel aux heat.
    They are not brand specific. So you may have trouble finding brand specific info.
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  3. #3
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    Quote Originally Posted by beenthere View Post
    A hybird/dual fuel system is any heat pump witha fossel fuel aux heat.
    They are not brand specific. So you may have trouble finding brand specific info.
    Sorry, I didn't mean to give the impression that I was looking for brand-specific information (at this point); I was really trying to find out if oil-based hybrid systems exist at all, or if I will need to design one myself.

    If such systems exist, then I can do some background research, and work with prospective installers, to decide which system will be best for my situation. The problem is that, while I've found loads of information on hybrid-gas systems, I've found none on hybrid-oil systems -- which gives me the impression that they do not exist.

    If such systems do not exist (in an integrated, manufactured form), then I will have to design a system with a new heat pump installation and my existing (or possibly a new) oil furnace. I'll need to find a contractor who can work with me in the design phase and then do the installation, which is different from finding someone who can install a manufactured system.

    So, the first question is, do hybrid-oil systems exist at all? As I said, I've found lots of info on hybrid-gas (NG and LP) systems, but none on hybrid-oil systems.

    Thanks,
    Vince

  4. #4
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    Quote Originally Posted by beenthere View Post
    A hybird/dual fuel system is any heat pump witha fossel fuel aux heat.
    They are not brand specific. So you may have trouble finding brand specific info.
    Whoops -- after another reading, I think I initially misunderstood your reply. When you say, "any heat pump with fossil fuel auxiliary heat," are you saying that the fossil-fuel system is triggered off the AUX HEAT line on the heat pump's thermostat? That is, instead of using electric aux heat, it uses the furnace? If so, then that's not the configuration I'm looking for. A heat pump's efficiency has likely dropped below the oil furnace's efficiency long before aux heat kicks in. I am looking to design (or purchase, if available) a crossover system that is based on outdoor temperature, which would switch over from the heat pump to the oil furnace at a pre-selected outdoor temp (say, 30 degrees F). (I'm also making the assumption that it would be undesirable to have them "overlap" -- e.g., between 20 deg F and 30 deg F they are both running, and then the heat pump fully drops out below 20 deg F; something of that nature.)

    Thanks,
    Vince

  5. #5
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    Quote Originally Posted by vsabio View Post
    Whoops -- after another reading, I think I initially misunderstood your reply. When you say, "any heat pump with fossil fuel auxiliary heat," are you saying that the fossil-fuel system is triggered off the AUX HEAT line on the heat pump's thermostat? That is, instead of using electric aux heat, it uses the furnace? If so, then that's not the configuration I'm looking for. A heat pump's efficiency has likely dropped below the oil furnace's efficiency long before aux heat kicks in. I am looking to design (or purchase, if available) a crossover system that is based on outdoor temperature, which would switch over from the heat pump to the oil furnace at a pre-selected outdoor temp (say, 30 degrees F). (I'm also making the assumption that it would be undesirable to have them "overlap" -- e.g., between 20 deg F and 30 deg F they are both running, and then the heat pump fully drops out below 20 deg F; something of that nature.)

    Thanks,
    Vince
    Yes, what you envision is typically how dual fuel setups are done. You'll have a heat pump and a coil along with your oil furnace. You'll also have a thermostat with an outdoor temperature sensor (preferably) that will switchover to oil heat at a preselected temperature. I don't know of any integrated/packaged dual fuel setup that uses oil--only gas. What brand you select for the heat pump/coil is up to you.

  6. #6
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    Done a fair amount of dual fuel heat pumps with oil as the second fuel.
    They are set up the same as gas dual fuels.
    You have 2 balance points to look at. Thermal, and economical.
    Unless your oil is very cheap, or your electric is extremely expensive. The heat pump will cost less per BTU then oil untill aboutt -10°F.
    Of course, the HP will not have been able to provide enough heat by its self long before that.
    You can set it up to always use the heat pump first, no matter what the OD temp is, as long as its above economic balance point. Thats the higher efficiency method.
    Or that the HP locks out at is thermal balance point and switches to oil, thats the comfort method.
    I have set them up both ways as far as control. Depends if the customer is looking for the best efficiency, or the best comfort.
    The only time that both run at the same time is when teh HP goes into defrost.

    If the company you choose has any dual fuel background, they can set up an oil dual fuel.

    What you may want to do. Is list what you want in performance from a dual fuel system.
    Comfort, or economy of operation. And then let your prospective contractors know. And give you suggestions from there.
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  7. #7
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    Thank you (both) for the information; this has been very helpful already.

    Let's suppose that I go with BeenThere's "comfort" approach, which requires an outdoor temperature sensor. (I figure if I understand the more complex approach, I'll better be able to tell if the prospective contractors understand it, too.)

    So, for the hybrid oil setup, it sounds as if I select a HP, and pair it with the existing oil furnace (or optionally purchase a new oil furnace, too -- not entirely out of the question, since the one that the former homeowner installed is a mid-range unit). I still need to do the research, but I'd likely select a high-efficiency heat pump -- min SEER 15 -- and install it in series with the furnace.

    Here's where it gets interesting. Reminder: I'm not an expert in this stuff, so please apply clue adjustments as appropriate. I'm also sure an experienced contractor will know how to do this. I'm trying to get up to speed so that I can (hopefully) tell the difference between an experienced contractor and one who hopes to become experienced by installing my hybrid system. :-)

    So: My inclination would be to install the heat pump *upstream* of the furnace -- i.e., on the intake side of the furnace -- reasoning being that the higher output temp of the furnace might "adversely affect" (read: melt? prematurely wear?) some of the internal heat-pump parts, which presumably are not designed for the higher temps that the furnace can put out. Does it matter?

    I would also want the system to be configured so that BOTH fans run whenever either system is active; this is solely to reduce back-pressure. Note: This is fan only; I'm not saying I'd have the furnace burning oil when the heat pump is running; I'd just have the fan run. Ditto for the heat pump when the system is reversed.

    Third: I need to find a way to cut over from one system to the other. The packaged/integrated hybrid-NG systems obviously have a way of doing this; is there any reason that I could NOT simply install whatever cutover they use on the hybrid-NG systems? AFAICT, it's just an outdoor temperature sensor that selects the active heating system based on outdoor temp. I could build one of these, but if it already exists, I'd rather use something that is already designed to do the job.

    Fourth: I assume that I would run two indoor thermostats -- one for the HP and the existing one for the oil furnace. (IIRC, a HP thermostat is different from an oil-furnace thermostat.) The outdoor temp sensor would be connected to a relay that would switch one thermostat "on" and the other "off," depending on the outdoor temperature.

    I have two prospective contractors coming in on Wednesday, so I need to get smart fast....

    Many thanks,
    Vince

  8. #8
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    I still need to do the research, but I'd likely select a high-efficiency heat pump -- min SEER 15 -- and install it in series with the furnace.
    Without a variable-speed blower, it's not easy to get 15 SEER, so you'll have to talk to your contractor and see if he has any available matchups with your size that can get close to 15 SEER or actually 15 SEER.

    I would also want the system to be configured so that BOTH fans run whenever either system is active; this is solely to reduce back-pressure. Note: This is fan only; I'm not saying I'd have the furnace burning oil when the heat pump is running; I'd just have the fan run. Ditto for the heat pump when the system is reversed.
    I'm not sure what you mean with 2 fans, but if you want to leave the fan on constantly, that is possible. There should be one blower...

    Third: I need to find a way to cut over from one system to the other. The packaged/integrated hybrid-NG systems obviously have a way of doing this; is there any reason that I could NOT simply install whatever cutover they use on the hybrid-NG systems? AFAICT, it's just an outdoor temperature sensor that selects the active heating system based on outdoor temp. I could build one of these, but if it already exists, I'd rather use something that is already designed to do the job.
    There are outdoor temperature sensors from companies like Honeywell. You can buy it as an accessory for Honeywell's touchscreen VisionPRO thermostats (which are very nice in my opinion I might add).

    Fourth: I assume that I would run two indoor thermostats -- one for the HP and the existing one for the oil furnace. (IIRC, a HP thermostat is different from an oil-furnace thermostat.) The outdoor temp sensor would be connected to a relay that would switch one thermostat "on" and the other "off," depending on the outdoor temperature.
    See above. There will be one "master" thermostat to control everything, including switchover.

    Look forward to seeing what the contractors have to say... Good luck.

  9. #9
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    The dual fuel HP will look just like a regular oil furnace with an A/C.
    You will have the oil furnace, on top of the furnace, on the air discharge opening, the coil will be installed.(no fan, just a coil, cased, or uncased as your install requires)

    Weather in HP mode, or cooling mode, it uses the furnaces blower to move the air.
    The coil should not be installed on the return side to protect the furnaces heat exchange from getting condensate in it in the summer, and rusting out.

    Several thermostats are dual fuel thermostats, that only require the outdoor sensor to control the dual fuel system. Must be sensor made for that thermostat.

    One thermostat will control both HP, and oil furnace.
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  10. #10
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    Thanks again. This has helped a lot -- my impression of how this would work was obviously way off. I'll let you know what the prospective contractors have to say ... should be interesting.

    - V

  11. #11
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    The term you'll want to use for a new thermostat is "two stage". It controls both the heat pump and/or your current furnace. On a two stage thermostat is something call "Emergency heat" or EM heat. That's another way of referring to using your current furnace.

    I have an old Honeywell two stage thermostat to better explain. Remember the old mercury switch round thermostats? Think of one with two mercury switches that are mounted to offset by 2 degrees - the first one dips to actuate HP and then the second one dips at two degrees below that to actuate your furnace. There are a few extra switches and and obviously extra wiring to make all this happen, but if you saw it, you'd understand the principal, albeit rather crude.

    Today's digital two stage thermostats are obviously a whole other breed: programmable, outdoor temperature sensor, remote indoor temperature sensor with averaging, remote indoor humidity sensor, EM heat lockout temperature, clean filter reminders, and the list goes on. I think there are some that let you plug in your current KW pricing and furnace fuel cost and guess at the best economic switchover - read beenthere's post about comfort vise economy.

    If you have a neighbor with a split system setup go check theirs out. I think you'll understand the setup pretty quick.

    I'm a cheap bastard so I'd be hesitant to throw out even a perfectly good mid range furnace without thoroughly checking out if you can mate a new HP to it. Call your furnace manufacturer and speak to tech support on what recommended HPs could be added to your system. They can probably even send you the installation guides to give you a better idea.

    Finally I hope you realize that an HPs heat is no where near as warm as a furnace because they produce less BTUs. This means they will run a lot longer, so be ready for your fan to run a lot. If your kids and pets like to curl up by the registers like mine in the morning, expect a few disappointed looks.

    Also as you approach the freezing point of water, HPs can go into defrost and the steam coming off can alarm many people - I'll bet there are many on this forum who have gone to service calls on that subject.

  12. #12
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    [QUOTE=dac122;1909982]The term you'll want to use for a new thermostat is "two stage". It controls both the heat pump and/or your current furnace. On a two stage thermostat is something call "Emergency heat" or EM heat. That's another way of referring to using your current furnace.

    Not all 2 stage stats are made for HP, let alone dual fuel capable, without the addition of a add on control.
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  13. #13
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    I met with one of the prospective contractors today (the other was a no-show); he appeared to be very well informed, and seemed to genuinely have quite a lot experience. He measured my oil furnace, and said there's only 23 inches for the HP coil, which seems to limit my choices to two 15-SEER systems -- Carrier and Trane. (I have a 4-ton outdoor unit. The Trane coil is 44kBTU, the Carrier coil is 48kBTU. He said that I would not likely be able to tell the difference between the two, either in terms of comfort or efficiency.)

    I described by furnace as "mid-range" (which I thought it was), and included the option to replace the existing furnace, in addition to simply adding a heat pump. The contractor checked the furnace, and said that it's actually a higher-end unit (80-some percent efficient), and recommended against replacing it. This is one of the reasons that I liked this guy from the start. (Well, that and he wasn't a no-show.)

    I included some air-circulation issues that we have in different parts of the house; he suggested a two-zone configuration, with electrically controlled dampers. (I have two main trunks coming off the furnace, so it is pretty easy to create a two-zone system.)

    He put together a proposal for what seemed like a very complete (i.e., well thought out), reasonable, cost-effective system, given what I have to work with (and some other considerations that I gave him. I liked that he wasn't pushing any particular system or manufacturer, but instead laid out the options available to me, and enumerated the pros and cons of each.

    Interesting aside: He recommended a crossover point around 35-38 degrees F for economy (low 40s for comfort), which is higher than I would have expected. He said that if the efficiency can drop significantly if the compressor has to go into defrost.

    Then, just in conversation while writing up the estimate, he mentioned that his house uses LP -- which reminded me that backup generators (which I also want to get) use either NG (which is not an option in my area), diesel, or LP. Converting to LP for heat would mean that I have single fuel for both heating and backup power -- an attractive option.

    So, in addition to the HP-only option (to be added to the existing oil furnace), I also had him quote a complete hybrid-LP system, in which the oil furnace would be removed and replaced by LP and a heat pump. (I also liked the fact that he wasn't pushing this solution, either -- he gave pro and cons, broke down the cost, and left the decision up to me.)

    Meanwhile, I've been researching LP costs, and here is where I run into questions. It seems that the cost of LP more or less tracks the cost of crude oil -- which means there is no long-term price advantage (i.e., I would not be able to decouple my heating costs from the cost of crude oil -- darn). It also seems that LP is more expensive per BTU than home heating oil -- which means that converting to LP would likely be more expensive than sticking with oil -- even in the long run.

    Is all of this reasonably accurate? I'm sure there are lots of factors to consider, so this is really a simplification of the situation -- but, to a first-order approximation, it seems that there is no advantage to switching from oil to LP. (Except that LP is ostensibly quieter than oil.)

    I'm trying to consider all of the [reasonable] options at the outset, so that I don't later find myself saying, "If only I'd known, I'd have gone a different route...."

    Many thanks for all of the information and feedback I've received. I felt that I was able to discuss the options I was interested in, and not sound like a complete idiot (or at least not as much of an idiot as I would have been without the help I've received from this site).

    - V

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