I am considering adding electric heat to my HVAC ductwork as a back up.
I currently heat with oil. My furnace is 92,000 BTU. Does anyone have insight to this? What size electrical heater would be required? Two stage? Could I install in-line with current system, or would I need to split and re-route by use of a damper and controls?
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Replies
Electric heat
Dave,
What problem are you trying to solve?
You say that the electric heat will be "backup." Will you install it because your 92,000 BTUH furnace doesn't provide enough heat? Or do you want electric heat in case of future oil shortages?
Electricitity is an expensive fuel, especially if used in the form of electric resistance heat.
Electric Heat
Backup incase of oil shortages or furnace breakdown in winter.
I have a heat pump but I am not convinced it will do anything for me during the coldest week in a Pennsylvania winter.
I suppose electric baseboard units in each room may serve as a better back up incase I would lose my forced-air blower, too. Ultimately, I would prefer gas and prepare to change my furnace which is 10 years old (no problems with it), but gas lines end about 300 yds and 2 properties away.
I have not done the math but I heard that electric heat is not far from oil anymore.
Any thoughts?
I'm guesssing that the most likely loss of heating ability would be a power loss due to ice storms or other weather events.
Anything that depends of electricity would leave you without heat.
Maybe a propane freestanding stove that can operate without electric power would be more reliable as backup.
Electric duct heating back up...
I have a generator that I run in the few cases we were w/o electricity. It will run the furnace but I am guessing it would be too small to run resistance heating for the entire house. I never considered propane. I guess I was too comfortable with the electric add-on being out of site. Your reply has me thinking a little more, though. Thanks.
Most heat pumps have "emergency"/"supplemental" resistance heating elements as well. Are you sure yours doesn't? (And how do you have the heat pump and oil furnace rigged to operate together?)
A lot of people have both around here. When the outside temperatuire sensor hits a low setpoint, the thermostat switches to the oil furnace. Problem is they both need electric, but a generator can easily operate an oil furnace. I keep a kerosene heater and a propane stove for emergencies, plus a small generator. Fortunately my furnace is natural gas, so I could run it off a generator, if I ever made an adapter to hook it up.
Electric duct heating backup...
I do not have any resistance heating in my air handler. My HVAC unit has a heat pump that runs down to external temperatures of 35-40 degrees, depending on where I set it. My oil burner runs below that. I usually control this manually, setting it to oil-only after October/November. When Spring arrives I adjust it back to the 35-40 degree mark so the heat-pump takes over again.
How hard is it
to make sure you have enough oil on hand, and enough gas to run the generator (for the air handler) during power outages? Then you have all bases covered. Since you say it would be hard to use the generator to heat the house with electrical resistance, how would adding heat strips to the furnace help you? Are oil shortages the main possible issue?
If you want another system, I would consider a ductless mini-split heat pump installed in a main area of the house. There are models that operate very efficiently down to very low outdoor temperatures. Find a way to power it with your generator.
A propane stove is also good backup heat for power outages but you would need a tank, gas lines, venting, etc.
A wood stove is another solution.
Just for curiosity's sake, what does oil cost per gallon, and what does electric cost per kilowatthour?
Electric duct heating backup...
I have a 330 gallon and a 250 gallon oil tank. I play the oil-price game and try to buy when it is low. I usually have oil. I also keep my generator full and 5-10 gallons of gas.
Really, my main concern is if myheating system would fail in the middle of winter. I keep spare parts and I have been able to get it running when it failed the past two seasons. I would prefer to switch over to a back up system so my family is comfortable while I either make a repair, or a contractor is repairing it. It can get awfully cold every hour there is no heat...and forget about a warm shower!
The cheapest oil prices have ranged between $3.25 and $3.60 per gallon since October. I think when you consider the entire electric bill it may breakdown to $.126/ KWH.
You've never made it clear -- is your oil burner a boiler or a forced-air unit?
Electric duct heating backup...
Hydronic furnace which heats a coil located in my unheated attic where my ductwork and blower are...
Sounds like the worst of all possible worlds -- you're likely not getting better than 60% efficiency.
But anyway, you can probably install maybe 20-35 BTU/hour (6-10KW, 25-40A) of duct heat without having to get a new electric service (though saying for sure would require a peek at your breaker panel). This would be enough to "survive" on should the oil burner fail, especially if you rigged it to only heat a few rooms in the house.
Where do you live, BTW, and what's the coldest winter temp you typically see? How big is the house?
Electric duct heating backup...
Live in NE Pennsylvania. Winters are not normally brutal...but cold. House is 2 story, ~3,000 sq.ft. Elec panel is 200a. We average 1,000 gallons of oil each year which of course is our hot water too. Last year we turned down the t-stat and used about 800 gallons. Keeping it down this year too.
I am leaning towards propane with an electric water heater...as back up.
Why not a propane water heater too? I don't like depending on electricity for a backup.
Energy costs
Your electric costs are fairly low, although making some assumptions about your ducts, electric duct heaters are not cheap to operate. I'd look at getting rid of oil entirely and going for a heat pump that will serve in your climate, preferably without ductwork. Out here the utility companies are really pushing mini-splits with rebates, and I can get one installed for about $3500 and then get a $1500 rebate. We have cheap electricity and expensive oil and propane so it's a no-brainer.
I'm guessing his HP 'emergency'/backup IS the oil heat.
It is my understanding that in my area an electric heat pump running at a COP of 2.5 (which it can down to about 25 degrees) is as cost effective as Natural Gas. Therefore, if you do not have NG then operating an electric heat pump down to a COP of 2 or even 1.5 still makes sense over Electric resistence heat. And a heat pump can operate at 1.5 at down to zero degrees. If this is all true for NG and if oil is more expensive than NG, then an electric heat pump seems like an answer.
When people say a heat pump does not make sense below 30 degrees it is becuase they are comparing it to NG forced air. But if you CAN NOT GET NG then it is a totally different ball game.
Here is a link for a propane 30k btu vented wall heater. This one does not require electricity, which I would find to be ideal for what you want. You may need a couple, or a different model. The store selling these has numerous non electric appliances for the type of people wanting that sort of thing which includes paranoid, certain religious sects, greenies, tree huggers, end timers, peak oil believers etc. I have ordered a couple things from them with quick service. They seem price competitive, but you may find the same type heaters in fireplace shops etc locally, and possibly dealer installed. Also, see the second link for propane wall furnaces.
I would avoid non vented appliances, but they would be OK for backup use.
You may find that using one of these heaters to heat rooms you spend a lot of time in will save a small amount of money if you lower the heat in the other parts of the house.
http://www.stpaulmercantile.com/index.php?action=store&page=WilliamsHeaters
http://www.stpaulmercantile.com/index.php?action=store&page=WallFurnaces
Why
would a tree hugger or peak oil believer want a propane heater?
Propane, gasoline and kerosene is popular with Amish, which is a certain religious sect. They use some modern equipment, but do not approve of anything that connects to the world of the Gentiles inside the house. I understand some groups do use natural gas at least for business use, but most would forbid it.
I don't understand their opposition to electricity, which they will use for powering their businesses, but only from a generator set.
Tree huggers don't want anyone else using propane, but like most of that sort of people, probably secretly, would use one themselves.
To answer your original question, electric "booster" heaters can be installed inline in the ductwork wherever there is clear access for service. They only come in certain sizes, of course, and so may not fit your specific ductwork without adapters.
92K BTU/hour would be 27KW, which is about 112A at 240V. It's unlikely that your house is wired for more than 150A, and may very well only be wired for 100A, so likely you cannot expect to produce the full 92K BTU of your oil furnace with electric resistance heating. Of course, the current furnace may be oversized, and you may feel that in an "emergency" you can get by with less heat, but you probably need a minimum of 40-50K BTU/hour.
That's probably a btu input figure, output may be only 60k btu. But, that's still too much power for any normal generator to run. That's why I proposed a propane unit that does not need electricity.
Keeping in mind that this is for "backup" heat, only in case of oil burner/blower failure, the operating cost for a day or three should not be of any significance. Base board electrical heaters are inexpensive. The major cost will be in the wiring installation, assuming the electrical panel is adequate. If you forego wall mounted thermostats and accept baseboard thermostats, the wiring labour/patching/painting will be even less. A bonus is every room is it's own "zone".
Some drawbacks: Remember to shut off each and every thermostat when not required. Heaters typically installed under windows where they may conflict with duct registers. Distance to/from drapery/furniture must be respected.
Good luck
92,000 would convert to somewhere around 26 KW electric heat. Yes, you could have an inline electric duct heater installed. Do you have enough electric panel capacity?
That being said ... I get the feeling you are making up solutions to problems you might be a little unsure about. You are potentially going to go through a fair amount of trouble and expense ... to ensure ... what exactly? Have you considered other options? e.g. a wood stove? Wood pellet stove? Dual fuel conversion of your boiler?
How old is the boiler? Maybe you should be considering replacement options if it is at the end of its useful life.