Cost of Propane Air Conditioning on House

Questions on how we spend our money and our time - consumer goods and services, home and vehicle, leisure and recreational activities
Post Reply
Topic Author
Point
Posts: 248
Joined: Mon Jul 10, 2017 9:33 pm

Cost of Propane Air Conditioning on House

Post by Point »

I'm in the process of purchasing a home and it has two rooftop air conditioning units. These are tied into the existing heating/ducting system in the attic below each unit, each on a separate level of the house, so there are two zones.

My original plan was to put in a large solar array to minimize the ongoing cost of electricity for the A/C. Now, I'm trying to assess what the operational cost of the propane might be on a monthly basis. This area is hot for 6 months of the year, getting into the mid to high eighties.

I know there are ways to calculate BPUs and compare propane vs electric, but at this point I'm just looking for practical experiences, ie, I have a house in that temperate range and run the propane A/C 8 hours a day, every day, and it costs me $xxx per month.

Downstream I'll probably change out the units for electric and the solar implementation/cost will offset the operational cost for the current propane usage.

So, what does it cost you per month to run a propane A'/C?

Thanks!
User avatar
David Jay
Posts: 9399
Joined: Mon Mar 30, 2015 5:54 am
Location: Michigan

Re: Cost of Propane Air Conditioning on House

Post by David Jay »

Have you seen the historic electric bills for the home? How do the winter and summer bills compare? Are the bills really that much higher in the summer? 80s in the daytime is not a huge AC load (compared to, say, Phoenix).

What is your time-frame on the solar implementation (how many years would you run propane)? It is hard to believe that you can purchase, install and run a propane system for less than the cost of continuing to run the current AC units for, say, 5-10 years.
Last edited by David Jay on Thu Sep 17, 2020 11:53 am, edited 1 time in total.
Prediction is very difficult, especially about the future - Niels Bohr | To get the "risk premium", you really do have to take the risk - nisiprius
User avatar
Wiggums
Posts: 2935
Joined: Thu Jan 31, 2019 8:02 am

Re: Cost of Propane Air Conditioning on House

Post by Wiggums »

Solar is still quite expensive, but money is not the only readon to consider clean energy. Having said that, you have to be very careful about the solar contract that you sign if you were not buying the system out right. You must also be very honest with yourself how long you’ll stay in that residence.
Flyer24
Moderator
Posts: 2111
Joined: Sun Apr 08, 2018 4:21 pm

Re: Cost of Propane Air Conditioning on House

Post by Flyer24 »

Topic moved to Personal Consumer Issues.
Valuethinker
Posts: 41162
Joined: Fri May 11, 2007 11:07 am

Re: Cost of Propane Air Conditioning on House

Post by Valuethinker »

Point wrote: Thu Sep 17, 2020 9:14 am I'm in the process of purchasing a home and it has two rooftop air conditioning units. These are tied into the existing heating/ducting system in the attic below each unit, each on a separate level of the house, so there are two zones.

My original plan was to put in a large solar array to minimize the ongoing cost of electricity for the A/C. Now, I'm trying to assess what the operational cost of the propane might be on a monthly basis. This area is hot for 6 months of the year, getting into the mid to high eighties.

I know there are ways to calculate BPUs and compare propane vs electric, but at this point I'm just looking for practical experiences, ie, I have a house in that temperate range and run the propane A/C 8 hours a day, every day, and it costs me $xxx per month.

Downstream I'll probably change out the units for electric and the solar implementation/cost will offset the operational cost for the current propane usage.

So, what does it cost you per month to run a propane A'/C?

Thanks!
You should be able to find Cooling Degree Day data for your locality. That would help you to compare w experience of others.

It wasn't clear to me why you would not go straight to solar array as propane system is unlikely to pay back in say 10 years? Solar panel have fallen so dramatically in cost. However if you have chosen that course of action then that's a diversion, here.
forgeblast
Posts: 390
Joined: Fri Oct 13, 2017 8:45 am
Location: PA
Contact:

Re: Cost of Propane Air Conditioning on House

Post by forgeblast »

Could you wait a year and take into account how you use the system and your own energy needs?
Topic Author
Point
Posts: 248
Joined: Mon Jul 10, 2017 9:33 pm

Re: Cost of Propane Air Conditioning on House

Post by Point »

The plan is to replace the propane AC to electric AC.

Degree day data:

Time Period:
February 01, 2018 - January 31, 2019
Annual HDD: 2899 °F
Annual CDD: 2183 °F
Valuethinker wrote: Thu Sep 17, 2020 10:21 am
Point wrote: Thu Sep 17, 2020 9:14 am I'm in the process of purchasing a home and it has two rooftop air conditioning units. These are tied into the existing heating/ducting system in the attic below each unit, each on a separate level of the house, so there are two zones.

My original plan was to put in a large solar array to minimize the ongoing cost of electricity for the A/C. Now, I'm trying to assess what the operational cost of the propane might be on a monthly basis. This area is hot for 6 months of the year, getting into the mid to high eighties.

I know there are ways to calculate BPUs and compare propane vs electric, but at this point I'm just looking for practical experiences, ie, I have a house in that temperate range and run the propane A/C 8 hours a day, every day, and it costs me $xxx per month.

Downstream I'll probably change out the units for electric and the solar implementation/cost will offset the operational cost for the current propane usage.

So, what does it cost you per month to run a propane A'/C?

Thanks!
You should be able to find Cooling Degree Day data for your locality. That would help you to compare w experience of others.

It wasn't clear to me why you would not go straight to solar array as propane system is unlikely to pay back in say 10 years? Solar panel have fallen so dramatically in cost. However if you have chosen that course of action then that's a diversion, here.
iamlucky13
Posts: 2085
Joined: Sat Mar 04, 2017 5:28 pm
Location: Western Washington

Re: Cost of Propane Air Conditioning on House

Post by iamlucky13 »

Please clarify: what is the current HVAC system? What is the alternative being considered? It is unclear to me from your posts what you currently have.

I lean toward investing a year living in the house and seeing what your utility cost is.

Propane is a relatively expensive fuel on a BTU basis - about equal to electricity, but the efficiency at the point of use for purposes other than heating is often lower. Without knowing the specs of the propane units under consideration, it's hard to give an opinion.

Whether or not to install solar is a largely separate question that depends on your local cost of electricity, how much sunlight you get, and any home specific factors like reasonable roof space or significant tree coverage.

Edit - we crossed posts. So this is an air conditioner you already that runs on propane (either an internal combustion engine instead of an electric motor, or an absorption cycle), not an electric air conditioner paired with a propane furnace for winter heating, right?

How old is the system? Is natural gas available and is a natural gas conversion possible?

For the heating and cooling degree days indicated, my default recommendation for new installation or replacement would be a heat pump, possible a multi-zone mini split system.
Topic Author
Point
Posts: 248
Joined: Mon Jul 10, 2017 9:33 pm

Re: Cost of Propane Air Conditioning on House

Post by Point »

iamlucky13 wrote: Thu Sep 17, 2020 1:00 pm Please clarify: what is the current HVAC system? What is the alternative being considered? It is unclear to me from your posts what you currently have.

I lean toward investing a year living in the house and seeing what your utility cost is.

--> we may do that

Propane is a relatively expensive fuel on a BTU basis - about equal to electricity, but the efficiency at the point of use for purposes other than heating is often lower. Without knowing the specs of the propane units under consideration, it's hard to give an opinion.

Whether or not to install solar is a largely separate question that depends on your local cost of electricity, how much sunlight you get, and any home specific factors like reasonable roof space or significant tree coverage.

--> California, Southern California Edison - very high rates; solar installation would be purchase and installed by a electrical/solar contractor we have used before. Our last solar cost recovery was < 4 years. The new location has full southern exposure, 4500' elevation, no obstructions to the east/south/west. Solar would not be on roof, on land with full southern exposure.

Edit - we crossed posts. So this is an air conditioner you already that runs on propane (either an internal combustion engine instead of an electric motor, or an absorption cycle), not an electric air conditioner paired with a propane furnace for winter heating, right?

--> The current propane AC units likely date back to the date of construction 1994; the labels are unreadable

How old is the system? Is natural gas available and is a natural gas conversion possible?

--> Natural gas is not available in this location

For the heating and cooling degree days indicated, my default recommendation for new installation or replacement would be a heat pump, possible a multi-zone mini split system.
iamlucky13
Posts: 2085
Joined: Sat Mar 04, 2017 5:28 pm
Location: Western Washington

Re: Cost of Propane Air Conditioning on House

Post by iamlucky13 »

I was pretty curious, so I did some more searching and did find that residential absorption cycle systems do still exist:
https://www.roburcorp.com/heat_pumps/ai ... mp_gahp_ar

It seems like it could make sense in areas where the electricity price is high, but the gas price is low, and there is a want for both heating and air conditioning in one unit, or for keeping the air conditioning running when the power is out with only a small backup generator. Since propane isn't very low price, I expect marginal economics at best.

From the spec sheet for the unit I found, it appears the cooling efficiency is comparatively low, as I expected, and it looks to me like it costs about $35 per million BTU of cooling delivered (assuming $2 per gallon of propane).

A mid-grade 16 SEER electric heat pump should consume in the ballpark of 70 kWh per million BTU when cooling, and the newest inverter driven mini-splits are even more efficient. For the following electric rates, that would be:

$0.10/kWh -> $7 / million BTU
$0.20/kWh -> $14 / million BTU
$0.30/kWh -> $21 / million BTU

So even with expensive electricity, a propane air conditioner doesn't seem like a great option, although perhaps it was more appealing 26 years ago, especially since it sounds like you also heat part of the year, and these units actually can save some money on heating. I suppose they also would be pretty quiet.

Overall, the costs reinforces my thought that a heat pump is probably a better option if all else is equal, or a regular air conditioner with a propane furnace for heat. At 26 years old, there is a risk it will need replacement soon anyways, so I'm not going to try to work out a ballpark annual operating cost to figure out a payback period . Unless there is a specific reason to rush, I'd still see how your costs are over the next year, but I like the idea of replacing it.

As for solar, if it made sense at your previous house in the same area, it almost certainly makes sense at the new house. Installing a heat pump or electric central AC would increase your electricity consumption, so the magnitude of the total savings of solar increases if you switch to electric HVAC.
User avatar
tyrion
Posts: 1278
Joined: Fri Feb 08, 2008 3:33 pm

Re: Cost of Propane Air Conditioning on House

Post by tyrion »

You didn't ask this, but in SCE territory and at that elevation I would look into Tesla Powerwalls if you go the solar route. At that elevation you are likely rural and at risk of electrical shutdown to prevent potential wildfires. I believe SCE still has SGIP funds available, along with the 26% federal rebate on solar+battery (if installed at the same time). Of course that assumes you can get it done this year, which might be tight on timelines.
Topic Author
Point
Posts: 248
Joined: Mon Jul 10, 2017 9:33 pm

Re: Cost of Propane Air Conditioning on House

Post by Point »

From what I can see, SGIP does not fit our circumstance since we won't have a well but will have services district water system, and finances are not an issue.

Tesla installs and support are a whole other question. Apparently there is great variability of opinion on those two issues. Regardless of the tight window for an install this year.
tyrion wrote: Thu Sep 17, 2020 5:38 pm You didn't ask this, but in SCE territory and at that elevation I would look into Tesla Powerwalls if you go the solar route. At that elevation you are likely rural and at risk of electrical shutdown to prevent potential wildfires. I believe SCE still has SGIP funds available, along with the 26% federal rebate on solar+battery (if installed at the same time). Of course that assumes you can get it done this year, which might be tight on timelines.
Topic Author
Point
Posts: 248
Joined: Mon Jul 10, 2017 9:33 pm

Re: Cost of Propane Air Conditioning on House

Post by Point »

iamlucky13 wrote: Thu Sep 17, 2020 5:26 pm I was pretty curious, so I did some more searching and did find that residential absorption cycle systems do still exist:
https://www.roburcorp.com/heat_pumps/ai ... mp_gahp_ar

It seems like it could make sense in areas where the electricity price is high, but the gas price is low, and there is a want for both heating and air conditioning in one unit, or for keeping the air conditioning running when the power is out with only a small backup generator. Since propane isn't very low price, I expect marginal economics at best.

From the spec sheet for the unit I found, it appears the cooling efficiency is comparatively low, as I expected, and it looks to me like it costs about $35 per million BTU of cooling delivered (assuming $2 per gallon of propane).

A mid-grade 16 SEER electric heat pump should consume in the ballpark of 70 kWh per million BTU when cooling, and the newest inverter driven mini-splits are even more efficient. For the following electric rates, that would be:

$0.10/kWh -> $7 / million BTU
$0.20/kWh -> $14 / million BTU
$0.30/kWh -> $21 / million BTU

So even with expensive electricity, a propane air conditioner doesn't seem like a great option, although perhaps it was more appealing 26 years ago, especially since it sounds like you also heat part of the year, and these units actually can save some money on heating. I suppose they also would be pretty quiet.

Overall, the costs reinforces my thought that a heat pump is probably a better option if all else is equal, or a regular air conditioner with a propane furnace for heat. At 26 years old, there is a risk it will need replacement soon anyways, so I'm not going to try to work out a ballpark annual operating cost to figure out a payback period . Unless there is a specific reason to rush, I'd still see how your costs are over the next year, but I like the idea of replacing it.

As for solar, if it made sense at your previous house in the same area, it almost certainly makes sense at the new house. Installing a heat pump or electric central AC would increase your electricity consumption, so the magnitude of the total savings of solar increases if you switch to electric HVAC.
This sounds reasonable. Wait and see what costs add up to, go solar, replace with heat pump or central AC.
Post Reply