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pende_tim
Premium
join:2004-01-04
Andover, NJ
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1 edit

Heat Pump + (Propane|Electric) Aux heat

Hi,
I am confused about the difference in operating costs between a Propane and Resistance backup heating system in a high efficiency heat pump.

I am getting ready to put in a 3T 18 SEER Goodman Heatpump with backup heating for a Delaware location. The house requires 30KBtuh cooling and 35KBtuh heating. Electric is 0.12/KWH and propane last year peaked at 2.80/gal as we get a bulk rate in the community.

Doing the math it looks like propane in a 95% furnace will give me 31,000BTU/$ and electric strips will give me 28,500BTU/$ so based on that propane is a better value.

However if I use the Bryant Operating Cost Estimator calculator propane will cost me about $120/year more than electric. If I increase the heating load, the spread gets bigger so it looks like propane is the more expensive choice. This is contrary to the raw energy cost comparison which shows propane should be a little more economical.

If I enter a A/C + strip heat and an A/C + Propane for comparison, the propane come out less costly to operate as expected. So why is propane mated with a Heat Pump more costly to operate than resistance mated with a Heat Pump?

Can anyone help me understand what is going on here?

Tim
--
The difference between genius and stupidity is that genius has its limits.

Mr Matt

join:2008-01-29
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You might want to check with Goodman to determine their assumptions. My heat pumps run until they need to defrost. The heat strips are turned on during the defrost cycle, usually only for a couple of minutes, and then are turned off when system reverts to the heat pump mode. The question is how efficient the propane heater is when operated in short cycles. During the defrost cycle, the propane heater will have to warm up to operating temperature before the defrost cycle can be activated without producing cold air during the defrost cycle. There might be other issues only Goodman can answer your question.

scooper

join:2000-07-11
Youngsville, NC
kudos:2
reply to pende_tim
It really comes down to how much each system will run - there is almost no doubt that the heat pump should run more than the propane furnace - the devil is in the details.

If your winters are pretty mild (like mine generally are) - and your electric rates work out - I can see where the HP + electric strips could come out cheaper. This scenario would be the case if your winters are mostly 20-25 degrees and warmer, with only an occaisional dip to colder. However - if your winters are much colder than that - the furnace starts making alot more sense.

One other thing to consider - I found out that my heatpump had died when we had 2 months in a row (in the winter) of electric bills in excess of $400 - because the house was being warmed by the heat strips. I have no doubt that having a propane furnace would have saved us significantly.

Also - if your the type that thinks about trying to keep the house warm during a power outage - it's much easier to run a furnace on a generator than it is to try to run electric heat strips
Expand your moderator at work


nunya
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O Fallon, MO
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reply to pende_tim

Re: Heat Pump + (Propane|Electric) Aux heat

Their math is wrong. For your 95%, you get 87,020 btu for $2.80.
For an electric furnace, the same 87,020 btu would cost you $3.06.
Your propane price is a little high, but I suspect it's because you are on the East coast. It is nice to have a backup fuel source in case of an outage. Even a small generator can run a propane furnace.
Electric resistance heat is actually terribly inefficient. Claims that it is 100% efficient are false. It's only 100% efficient at the point of use. The actual efficiency is around 40-50% after generation and transmission losses.
--
If someone refers to herself / himself as a "guru", they probably aren't.


SwedishRider
Rider on the Storm
Premium
join:2006-01-11
not Sweden
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said by nunya:

Your propane price is a little high, but I suspect it's because you are on the East coast

Possibly, but also depends on tank size and ownership/leasing. Propane here in CT with a customer-owned 500-1000 gallon tank is hovering around $1.60/gal right now.


pende_tim
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join:2004-01-04
Andover, NJ
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1 edit
reply to nunya

Yes a agree with your math, nuyna. Those prices are exactly what I calculated and is the basis for this post.

In the cold light of day it occurs to me: Could the lower operating cost for electric be due to the fact that the HP compressor section is "off" below the balance point of the outdoor thermostat and the system runs only on propane? The electric model uses the Heat Pump and the electric strips below the balance point, correct? Even though the heat pump can't provide the total heating required below the balance point, it will still contribute something to the heating at a higher efficiency than the propane furnace.

Even though the price is high compared to your area and JimCT's experience with owned tanks, it is all relative and depends on the market. Last year while I was paying 2.80, people outside the community were paying 3.30/gal.... ouch.
--
The difference between genius and stupidity is that genius has its limits.

scooper

join:2000-07-11
Youngsville, NC
kudos:2
reply to pende_tim
Again - it depends on how your system is setup. On mine - with the thermostat on "Normal" heat mode - It's going to run the heatpump except for
A) - I'm asking for too big a temperature delta for the heatpump alone to get there efficiently (happens, because I use a programmable thermostat with setback while we are sleeping)
B) - It's cold enough outside that the heatpump can't keep up (usually below that 20 degree F point)

On Emergency, it should run the furnace exclusively, but I need to get a good HVAC company out here to get this fixed so it works correctly.

BTW - I do NOT have a thermometer connected to the HVAC system - just my indoor only thermostat.

ncbill
Premium
join:2007-01-23
Winston Salem, NC
Reviews:
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reply to pende_tim
So how do you heat your home with a heat pump when the power goes out?

You want propane back-up for that scenario.

Surely if you buy your tank you can get a better price/gallon?

scooper

join:2000-07-11
Youngsville, NC
kudos:2
You either don't or you get something like a kerosene heater / small propane heater that is rated for indoor use.

Even with the propane furnace - you still need a generator to run the thing (fan, controls, etc.).

I've been fortunate that my longest power outage has been 24 hours, when Hurricane Fran struck and came all the way to Raleigh.


alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1
said by scooper:

You either don't or you get something like a kerosene heater / small propane heater that is rated for indoor use.

Even with the propane furnace - you still need a generator to run the thing (fan, controls, etc.).

You'd be surprised how small of a generator is needed to run a gas furnace.
A small inverter 1000w would do, and also be able to run your fridge.

Now for the cost of electric vs gas, it's also about the price you pay per cubic foot of propane and the price per Kw/h. Then you calculate what each gives you in $/btu.

When I did the math for NG vs electric, they came down to the same.
A heat pump does throw in a curve ball though. It is hard to know if it will save you it's cost in heating energy savings. If it is too cold, a heat pump is useless, then you switch to propane.


pende_tim
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Andover, NJ
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reply to ncbill
said by ncbill:

So how do you heat your home with a heat pump when the power goes out?

You want propane back-up for that scenario.

Surely if you buy your tank you can get a better price/gallon?

I can not put in my own propane tank as the developer had Sharp Energy install the gas lines in the community ( at no cost to the developer ) and then the developer put a prohibition in the HOA that disallowed individual tanks. Sharp Energy has us captive for the next 25 years.
--
The difference between genius and stupidity is that genius has its limits.


alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1
said by pende_tim:

then the developer put a prohibition in the HOA that disallowed individual tanks. Sharp Energy has us captive for the next 25 years.

Can't it be overruled by majority vote? It's not like the HOA has any power if NOBODY wants to enforce that rule.


nunya
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They do that a lot in trailer parks around here. The system is pretty much the same as the normal gas company.
Very large propane tanks are located on the park property. Each trailer house that connects gets a meter that looks just like a regular NG meter.
It's starting to catch on in rural subdivisions as well. The regular gas company doesn't go out too far past the suburbs.
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If someone refers to herself / himself as a "guru", they probably aren't.

Mr Matt

join:2008-01-29
Eustis, FL
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1 edit
reply to pende_tim
I would check how your deed restrictions are enforced. My brother purchased a house in an area where they had piped in propane installed as a temporary solution. There was a form he signed at closing, that acknowledged that the gas company reserved the right to convert the fuel from propane to natural gas when a natural gas pipe line was extended to the sub division. The form also indicated that the gas company would convert all appliances from propane to natural gas at the gas companies expense when natural gas was available. About ten years after he purchased the house the entire subdivision was converted to natural gas. His furnace and water heater were converted at no cost to him.

On the other hand some building departments operate in collusion with developers and utilities and will not issue a building permit or approve an installation of a service unless the homeowner presents a letter from the HOA or utility approving the installation. Some service providers will not do any work in a sub division that has deed restrictions unless the homeowner provides a letter from the HOA approving the work.


toby
Troy Mcclure

join:2001-11-13
Portland, OR
reply to pende_tim
When I got rid of our propane tank and got a new all electrical heat pump/resistive heat strip furnace, I also took into account safety and hassle.

It is safer to use electric, less fire risk, no noxious gases, the furnace will last a little longer. The cost for us on the west coast was about the same, as propane has sales tax on it, electric does not, electric is regulated a small amount too.


mityfowl
Premium
join:2000-11-06
Dallas, TX
reply to pende_tim
said by pende_tim:

said by ncbill:

So how do you heat your home with a heat pump when the power goes out?

You want propane back-up for that scenario.

Surely if you buy your tank you can get a better price/gallon?

I can not put in my own propane tank as the developer had Sharp Energy install the gas lines in the community ( at no cost to the developer ) and then the developer put a prohibition in the HOA that disallowed individual tanks. Sharp Energy has us captive for the next 25 years.

I would think any natural gas supplier would be cheaper than propane.


No gas

@mycingular.net
said by mityfowl:

said by pende_tim:

said by ncbill:

So how do you heat your home with a heat pump when the power goes out?

You want propane back-up for that scenario.

Surely if you buy your tank you can get a better price/gallon?

I can not put in my own propane tank as the developer had Sharp Energy install the gas lines in the community ( at no cost to the developer ) and then the developer put a prohibition in the HOA that disallowed individual tanks. Sharp Energy has us captive for the next 25 years.

I would think any natural gas supplier would be cheaper than propane.

Some developements beyond the reach of NG will install bulk LP tanks and provide metered service to each lot. Sounds like this how the OP's development is set up. As previous poster has mentioned, trailer parks do this too.

Mr Matt

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reply to pende_tim
You might want to check to see if Sharp Energy also distributes natural gas. As I said in a previous post my brother lived in a development that originally had piped in propane but within ten years the supplier switched to natural gas. Check with Sharp Energy to find out if they will be converting to natural gas in the near future.

Here in Central Florida a developer that was building about four Miles from my home wanted to install natural gas. The nearest natural gas source was three miles away. The natural gas suppler installed a large capacity natural gas storage system to supply the subdivision until the natural gas line could be extended three miles to the subdivision.


pende_tim
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join:2004-01-04
Andover, NJ
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Hi Mr Matt,
If NG were available I would be all over it. There is none within 10 miles of here and the large buried tank (10,000 gal?) has propane which is what the community is setup to use.

I will give them a call anyway.
--
The difference between genius and stupidity is that genius has its limits.


cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to alkizmo
said by alkizmo:

You'd be surprised how small of a generator is needed to run a gas furnace.
A small inverter 1000w would do, and also be able to run your fridge.

Likely not. A fridge takes way more than 1000W on startup. Sure it drops to ~150W after 30 seconds, but the startup current would cause the inverter to shut down.


alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1
Not that much more, but true that with the furnace blower running it would too tight.
Meh, a 2000W inverter isn't that much more expensive


cowboyro
Premium
join:2000-10-11
Shelton, CT
said by alkizmo:

Not that much more, but true that with the furnace blower running it would too tight.
Meh, a 2000W inverter isn't that much more expensive

I've noticed significantly high peaks on occasion (in the neighborhood of 18A->2100W) Considering that typical inverters give a stepped square wave and not a sine, you may be in for a surprise and have even higher peaks.


cowboyro
Premium
join:2000-10-11
Shelton, CT

1 edit
reply to pende_tim
said by pende_tim:

I am getting ready to put in a 3T 18 SEER Goodman Heatpump with backup heating for a Delaware location. The house requires 30KBtuh cooling and 35KBtuh heating.

At what temperature does it require 35k BTU of heating and with what temperature inside?
That is the key question you need to ask. You cannot and should not make a decision until you know the answer.

I'll give you my house for example. The lower floor has ~1400sqft. Good windows, average insulation. I have a 2.5-ton heat pump serving the floor. It only handles well down to 30F with 74F inside.
"Handles well" means it does not need backup heat, that's the threshold for 100% duty cycle.
If I were to replace the unit I'd install no less than 3.5-ton.
Also keep in mind that in order to save more money you need to be able to use setbacks; if the unit is undersized it can barely deliver enough heat to maintain the temperature so it will be unable to recover after a setback without using backup heat and eating all the savings (and maybe more).


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
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That 35k BTUH demand is at 13*F OAT and 72* inside from the Manual J. Looking at the curves for the heating load and heating supply, it looks like the balance point will be about 30*F.

This temperatures is exceeded about 95% of the time during the daytime heating season. At night the OAT will get down to 20*F briefly. However the temperature will be setback a few degrees as we are under the covers so propane use will be minimal (I believe!).

I will, of course, have to play with the amount of night time setback to keep the fossil fuel use minimized.

I did consider a 4T unit but since the main driver for this project is the summertime cooling and comfort, a 48,000 BTUH unit would be really over-sized and humidity would be a major issue.
--
The difference between genius and stupidity is that genius has its limits.


cowboyro
Premium
join:2000-10-11
Shelton, CT
said by pende_tim:

At night the OAT will get down to 20*F briefly. However the temperature will be setback a few degrees as we are under the covers so propane use will be minimal (I believe!).

Not quite...
This is my furnace use (hours of burning oil) between Nov 1, 2011 and Mar 1, 2012
0, 2.8822
1, 3.0511
2, 3.9567
3, 3.4833
4, 3.9211
5, 6.7611
6, 7.1600
7, 21.0253
8, 12.1131
9, 6.8856
10, 4.7722
11, 4.1100
12, 3.3511
13, 3.9667
14, 3.9389
15, 5.2400
16, 3.9144
17, 4.3678
18, 5.3922
19, 5.5556
20, 6.7033
21, 8.1522
22, 4.5411
23, 1.9667

35% of all my oil use was in a 4-hr span between 5:00AM and 8:59AM
That with a lower setback than usual.

said by pende_tim:

I did consider a 4T unit but since the main driver for this project is the summertime cooling and comfort, a 48,000 BTUH unit would be really over-sized and humidity would be a major issue.

Consider a 2-stage unit and variable speed air handler. That will take care of any humidity issue.


alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1
reply to cowboyro
said by cowboyro:

I've noticed significantly high peaks on occasion (in the neighborhood of 18A->2100W) Considering that typical inverters give a stepped square wave and not a sine, you may be in for a surprise and have even higher peaks.

Yes I'd be surprised, and disapointed in inverter generators

I wonder if inverter generators have a starting wattage like non inverters. My generator has 3000W running rating, but can go up to 4000W for starting (Short duration).

I admit that even then, my furnace blower takes a little bit longer to get to full speed while on the generator though.


pende_tim
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Andover, NJ
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reply to pende_tim
I think I may have found the reason for this paradox.

With a Fossil fuel (dual fuel) furnace mated with a heatpump, the heatpump is turned off when the fossil fuel is turned on. This is based on outside air temperature and the cutover point is called the "balance point". In my case that would occur at about 30*F. So at times when the outside is below 30*, I would be burning propane only with an efficiency of 95%.

A system with electric strip heaters however, locates the strips in the duct so that the heatpump and the strips can be on at the same time. The key here is that the strips work at 100% efficeincy but the heat pump still has a decent COP well down into the 0*F range. In fact at 0*, my system should have a COP of 2.0 which is giving me 2x the heating efficiency of strip heaters.

This means that while the strips are on, I am also getting some "free" energy from the heat pump. This efficiency continues well below the fossil fuel balance point.
--
The difference between genius and stupidity is that genius has its limits.