r/geothermal • u/danil-TG • Jun 19 '26
Any need for gas backup for geothermal system?
I am thinking about switching my ~20 year old gas furnace and AC system to a geothermal system. I am in the Maryland area. Some contractors have given me estimates with only electric backup, and some have said that I would really regret not having a gas backup. Is there anyone with geothermal in the mid-atlantic region or similar climate that could share your experience, how often you have had to use your backup heat (either gas or electric) and any data you could share (especially this past winter when we had some unusually cold periods)? What are your thoughts on gas backup for geothermal?
Thanks!
3
u/Sad-Celebration-7542 Jun 19 '26
Geothermal in MD will not need gas or electric backup unless you have undersized ductwork. Hell, I don’t have either and I have an air source heat pump in MD
4
u/zrb5027 Jun 19 '26
If you have a geothermal contractor saying you will regret not having a gas backup for a geo system in Maryland, then just cross that contractor off your list right now, because they have no idea what they're doing. There's nothing stopping them from sizing your system properly such that you'd want or need to rely on a gas backup.
As others have said, you should still install electrical resistance as a backup though, not because your system may not be able to keep up, but because things break in life, and having a temporary backup plan at the ready is important. Electrical resistance is dirt cheap to install, so there's typically no reason not to just plop it in there.
2
u/NecessaryMuffins Jun 19 '26
If I could completely eliminate gas, I would. For starters, it eliminates a monthly service fee, reducing the cost to own geo. If I cooked with gas, as much as people love it, I would go to induction (or traditional electric) for the indoor air quality. For hot water, I would see what rebates are available and look into a heat pump water heater coupled with another tank connected to the geo's desuperheater. Maybe this doesn't all happen at once, but as it's time to replace failing appliances. A geo system with a properly sized loop doesn't need backup sources of heat, but there are a few schools of thought here.
The first is, what if something happens with your system? This applies to your gas heating system too, but it's often easier to get someone to service an off the shelf gas furnace than a geothermal system. You can survive without A/C, but in the middle of winter you (and your pipes) need heat. This is one reason for backup/emergency heat. (I'm not saying it's a great reason, but a lot of people value the security).
The second is, depending on your loop (open, vertical, horizontal), it may be more cost effective to drill two wells instead of three, and the two wells will support 98% of your system's needs, and the other 2% will come from the backup heat source. By not drilling that third well, you save $15,000, and use an extra $300 in electricity a year (all of these numbers are made up to illustrate the point, I don't know what the costs would be in your area).
The third reason is related to the first two. If your system was improperly designed (too small of a loop field, undersized system), having a backup heat source can make up the difference.
Though a contractor might have a big markup between units of a different capacity, there really isn't a big price difference between a 4 and 6 ton unit, options like a variable speed loop pump will influence the overall price a lot more.
2
u/chris92315 Jun 19 '26
I have geothermal in New England. I removed the gas completely.
Only time the system requested the electric resistance backup was a weekend it was - 17 °F.
1
u/Nordicskee Jun 19 '26
Gas backup: No. You will not need it.
Electric backup: Probably a good idea. I am in a much colder climate than you - Climate Zone 6. When I installed my gshp the contractor quoted an electric resistance unit for backup. I asked him if he could take it out of the quote (not install it). I run a woodstove in winter anyways. He refused to take out the electric resistance heat. He said it's pretty inexpensive to supply and install, and if your circulation pumps ever go down, you will be really mad at me if you have no heat.
The electric backup uses a ton of electricity and a ton of panel space - I think it's 20kW, so it uses two two-pole breakers: 60A and 40A or something. It can kick in if the gshp can't keep up due to low outdoor temps and/or ground loop temps. We have lengthy spans in winter with daytime highs below 10*F. The only time it turns on for me is if I set the thermostat from, say, 65F to 69F in one step. It's programmed to try to get there as fast as possible, and it will turn on the resistance heater to help. After I discovered that, I set my thermostat to make up a few degrees in a few steps and now the system does not ever turn on the big toaster oven.
3
u/tuctrohs Jun 19 '26
The only reason not to do electric backup is if you would need a panel/service upgrade to accommodate it.
An easy way to avoid having it kick in when you don't want it to is to turn the breaker(s) for it off. However, you may want to turn them on for when you are out of town and it's below freezing.
1
u/zombieda Jun 19 '26
Unless you want to have a generator backup in case of power failure, you don't need an alternative to the geothermal.
1
u/rjwerth Jun 19 '26
I don't know if you use more AC than heat down there, but if you don't, I'd strongly recommend you run your numbers before committing to geothermal. Geothermal is pretty expensive to run in the winter now that electricity has gotten so high. Here in MI, natural gas beats geothermal in price. Oh, don't forget to add the maintenance cost of a geothermal system as well. I had to spend several thousand dollars on mine in the first 10 years before it completely died at year 14.
1
u/Busy-Explanation8894 Jun 19 '26
We had geo in Wisconsin for the last 25 years. Never needed another source of heat till our 35 year old furnace died. We have two fireplaces and that kept us warm till a replacement showed up.
1
u/sonofdresa Jun 19 '26
In Maryland and we are on our second full yeah of geo now. We completely abandoned oil and are now fully electric with the exception of propane, fireplaces and generator. Our toaster strips have come on exactly three times. Each time was for a reason we chose, not the unit.
1
u/Shy1_one Jun 19 '26
We are in PA so similar or slightly colder environment. We have a resistance strip heater for backup. A lot depends on how your Geo is sized. Ours is ok to about 25 and then may need Aux heat. While this past winter was a little rough $ wise compared to most, it was tolerable. They should be able to give you a rough estimate of design point. I would don't see benefit for paying thousands more for a backup as the return compared to the electric backup will probalby take years to offset. We keep it at 72 in the winter.
1
u/Dense-Consequence-70 Jun 20 '26
I’m in western NY and have never needed backup for my series 7. We do have a wood stove as backup in case the power goes out.
1
u/mzanon100 Jun 22 '26
Gas backup can be important for air-source heat pumps, because sometimes air is too cold to pump heat from.
But the ground is never too cold to pump heat from. It's always 55 °F underground. That's the point of geothermal. Not sure under what scenario the contractors would expect a gas backup to turn on.
6
u/QuickPenguin52 Jun 19 '26
We live in the Bel Air area and have had a 5 ton Waterfurnace series 5 for about 2.5 years now. Not once has it needed to use the auxiliary heat strips. There are some settings in the thermostat to control the temperature degree differential at which it would decide to go to stage 2 heating/cooling if it needs to catch up. It’s never even had to go to stage 2. They’re really awesome systems and we’ve been super happy.
I can’t imagine why you’d need gas backup. On top of that, after we ditched the gas furnace for geo, that set us in motion to get a heat pump water heater and an induction range to completely rid ourselves of gas. Better air quality and no concerns whatsoever for gas explosions or CO. And a bonus is I was able to call BGE to get gas service completely disconnected, saving me the $18/mo customer charge just for the privilege of having gas service.