Pros and cons of gas vs. electric for DHW, cooking, and in-floor radiant heating?
Pinoli
| Posted in Mechanicals on
We are building a 2000 sq.ft. Single story, ‘pretty good house’ in zone 6B in Colorado in a small town with both reliable electricity an natural gas. We are weighing the pros and cons of gas powered v electric powered system for DHW including the infloor radiant heating. If we set aside the issue of fossil fuel use, what are the pros and cons of each? Thanks in advance.
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User-6885857,
First of all, can you tell us your name?
If you want to "set aside the issue of fossil fuel use," you shouldn't post your question on a green building web site. For environmentalists, it's impossible to set aside the issue of fossil fuel use, which happens to be the greatest environmental threat to life on our planet.
Most green builders design all-electric houses. If their local electric company offers a program for the purchase of wind-powered electricity, they sign up with the program. If possible, they install an on-site photovoltaic (PV) system to balance their annual energy use.
For more information on the gas leaks associated with our nation's natural gas pipeline system -- leaks that are contributing to global warming -- see Natural Gas Pipelines Are Leaking .
Since natural gas has become so inexpensive, many electric utilities have begun to use it instead of more expensive and more polluting sources, such as coal, so even if you use only electricity for heating, you are, more than likely, using some natural gas.
That said, from an economic standpoint, it really depends on the rates for each source, and the efficiency of the heating source. IOW, you have to do the math,
Natural gas pros:
1. For heating purposes, it is often cheaper on a BTU basis.
Natural gas cons:
1. Burning natural gas contributes to global warming.
2. Natural gas pipelines leak methane, a potent global warming gas.
3. Natural gas utilities charge a minimum monthly fee, even during months when no natural gas is used. Avoiding this minimum monthly fee is a big benefit to owners of all-electric homes.
4. When a house has fuel-burning appliances, there are increased worries over providing adequate makeup air and preventing backdrafting.
You have received good feedback that I all agree with. I will point out a reason to consider natural gas though.
In times of disaster, perhaps with the exception of earthquakes and extreme flooding, natural gas infrastructure may be up and running while other above ground electric utilities are out of service. For example after hurricane Sandy where we used to live in NJ we had no electricity for a number of days, except that we provided with our own small generator. However we had town provided water and natural gas. Our old pilot driven hot water heater kept on cranking along; it was pretty nice.
For much the same reason as above, in the new energy efficient home that we built a few years ago we installed a propane range. Comforting to know that we can make a bowl of soup if all else fails. (The other reason for the propane range was desire expressed by the cooks in the family. That is a preference that has been dissected extensively on GBA.)
Martin,
I am responding to your first answer to my question. First off, there is no place on my PC to type my name formally, though there is a line, it does not take it. Sorry, Lydia S Segal
Second, I am an environmentally aware and am only three months into understanding anything about building a house. I have been reading alot, especially this website and your excellent articles and answers to other questions.
I am sorry if my question offended. I see a fair number of questions and articles about gas powered devices/mechanicals. So I thought it would be ok to ask the question. It seems to me, there are pro and cons beisde the obvious environmental, those being the efficiency, the economics and maybe the logistics. By logistics I mean; simplicity and local availability of install and maintenance (should my spouse go before me, I am in trouble!) and the ability to lock and leave allowing us to go on vacation etc.
I want to know what issues or questions I am NOT considering. I/we are too new to this to even understand the questions. As an example three months ago when we told our architect we wanted to built a passive solar house, we did not realize there was something called a 'passive hauz' requiring certification, which we don't have any interest. We are catching up from insulation materials to windows to target R values.
With radiant floors the additional cost of a hydronic heatiing system (whether gas or electric boiler) is probably better spent on rooftop solar.
A 2000' Pretty Good House in sunny high-altitude 6B Colorado can probably hit Net Zero Energy with a PV array that fits on the house if the heating system is a combination of inexpensive electric mesh radiant floor (for maximal cush-factor) running off a floor thermostat, and a cold climate mini-split or two for maintaining the room temperature(s).
If you want hydronic radiant floors for other reasons, then note that they can be highly energy efficient when supplied by an air to water heat pump (such as Chiltrix). And that such a system could be combined with water storage to utilize PV solar without relying on net metering or batteries.
Economic issues are highly effected by how long you intend to keep the house.
I don't like the indoor pollution caused by cooking with gas.
Lydia,
Thanks for sharing your name, and welcome to GBA. I can assure you that your question did not offend me. I just wanted to point out that it's hard for green builders to set aside the question of fossil-fuel use.
You're right that GBA covers questions related to gas-burning appliances. That said, many of these questions are more relevant to owners of existing homes than to people planning to build a new home. If you are designing a new home, and you are interested in "green" solutions, you'll find that most advice on this web site leans toward the all-electric approach.
You will also learn that we tend to discourage people from installing in-floor radiant heating systems. To learn why, see All About Radiant Floors.
I give up, just read the article Martin suggested. No plan for AC, no plan for ducts. Plans for hiking and biking and skiing....and beer. Back to the drawing board after reading the 'All about radiant floors' article.
Maybe mini splits in the great room and master for heat, no cooling, as at 7000 ft in Colorado with 7000 HHD, not necessary. urgh
Any mini-splits that can heat will also cool, whether you need to run it in that mode or not, it's there.
In a well designed solar tempered Pretty Good House, you may find there will be days when some amount of active cooling is useful, though night time ventilation strategies usually work just fine in your area.
Cheap low-voltage mesh radiant floors can still be a nice comfort feature in places that might matter (say, in bathrooms). When used judiciously it won't impinge heavily on the average heating efficiency of a house heated with mini-splits.
Start with the right load numbers before starting in on the mini-split spec. The heat load calculations are best done by an engineer or RESNET rater- heating contractors have a pretty lousy track record on getting it right even with standard code-min construction, and it's even worse when it comes to high performance houses.
Then, at 7000' it's important to do the homework on capacity derating for altitude on the mini-splits. Some mini-split installers understand it, but (sadly) most won't. have more than a clue (assuming they're even aware of the issue at all.)
Lydia,
Building an efficient and comfortable home is a bit challenging but well worth the hassle factor. That hassle will be less of an issue if you partner with professionals who specialize in green construction. You might want to begin by talking to a few architects and/or home designers.
Lydia,
One more point that we often emphasize here at GBA is that it's best to invest a little bit more in your thermal envelope (your insulation details, air-sealing details, and the performance specs of your windows) than it is to invest extra in your heating system.
If your home has a low rate of air leakage, and above-average levels of insulation, it won't require much heat, and your heating system can be small and inexpensive.
Martin etal.
Thanks for all the suggestions. We have been working with an excellent local architect, Sarah Whittington and a regional engineering group to get recommendations on energy efficiency, R value targets, insulation package etc. and of course reading here.
Your suggestion about going all electric is a good one, though it leaves me in a conundrum as the local energy company Xcel, states on their web page for Colorado, 45 % from coal and 25 % energy derived from natural gas. So no escaping non renewables. Local ordinances mandate grid connection.
Much to consider, thanks for all the help. Lydia
Lydia,
Xcel offers a program called Windsource to residential electricity customers. It's a voluntary program that allows you to buy electricity generated by wind turbines. Here is a link to a site that explains the program: Windsource for Residences.
In addition to buying lo-carb electricity, GENERATING your own with rooftop PV benefits to the local distribution grid by lowering the peak & average load on the grid, and is still cost effective against the standard retail rate when net-metered. Being connected to the grid, when your PV output exceeds your load and exporting to the grid your power exports are offsetting fossil-fuel use, and lowering the amount of power being transferred on the local grid & transmission grid. (Your power is effectively going from your house to your neighbor's house.)
When buying wind power from a remote wind farm it is putting power onto a transmission grid that's offloaded at a substation to your local distribution, which is quite a bit more infrastructure use.
The rate of renewables going onto the grid in Colorado is increasing, and the capacity factors (basically the amount of operating time and intensity) of the coal & gas generators is shrinking. There has been some shifting of capacity factor from coal to combined cycle natural gas now that gas is cheaper (and gas fired generators are more flexible), but wind power is now even cheaper than combined cycle gas, and 20 minutes into the future (OK, maybe it'll be 20 months... :-) ) utility scale solar will be too. So even if it's a heavily fossil fired grid in September 2017, within the lifecycle of your heating system that is likely to change dramatically.
At higher elevation the annual output of rooftop PV is higher than it is at sea level, which makes the economic value of residential rooftop PV at 7000' in Colorado higher than in say, a hilltop in Connecticut at 700', despite the fact that grid electricity in CT is dramatically more expensive than grid electricity in CO (about 20 cents/kwh vs. 13 cents.) If you can, design and plan the house for Net Zero Energy, or even net-positive energy, since virtually all cars & trucks sold in 2025 will be electric drive, with a battery (even if it's a hybrid.) This stuff is coming on much faster than most people realize.
Lydia,
You are likely to have a fairly small winter heating load if you are exploiting the sunny winter climate of Colorado with some variant of passive solar design (larger or more south windows, smaller or fewer windows elsewhere, more insulation and air-sealing, and thermal mass (e.g., concrete slab floor, with additional heating elements imbedded or not). It is possible that the amount of heat you will need even during the coldest "design temperature" days or overcast days will be fairly small. You may not be able to cost-justify a central heating system. The inexpensive electric mesh radiant floor or mini-splits noted by Dana are likely to be all you need. I installed electric radiant heating in the ceiling in a passive solar home in Boulder on the first floor with a concrete slab floor, and only used it once in five years. Upstairs bedrooms used radiant electric heat on about a third of nights during mid-winter. This 1980's house might barely meet today's "pretty good house" level of insulation and air-sealing, but was passive solar. You can calculate the wintertime solar heat gains and heat losses to design a passive solar home that works well in Colorado, an ideal cold sunny climate for passive solar wintertime space heating.
Martin, Dana etal,
Wind power: I appreciate the info you both sent. One question, how does one know that they are actually getting their electricity from a wind source versus a non renewable? Isn't it all mixed in the grid?
Please remember no laughing at this question, I am new to all this, lydia
Lydia,
Utilities that offer customers the option of buying wind power use accounting methods to justify their programs. If customers who purchase 25% of the utility's electricity sign up for the program, then the utility needs to be able to show that 25% of the electricity it distributes is sourced from wind turbines.
The utility programs that offer "green power" options to ratepayers are not allowed to count that power purchased as part of their standard grid mix, or credit it toward any state mandated renewables portfolio standard. So when you're buying say, 100% wind power through the utility (or an electricity broker) you really ARE paying the wind power generators for their output over and above what the utility would otherwise be buying, which in many ways is similar to paying for the power from your own rooftop solar PV.
With grid-tied PV you're exporting to the grid whenever your instantaneous power draw is less than what your solar is producing, drawing from the grid whenever your load is greater than immediate output of the solar. It is offsetting whatever the grid-mix is at the moment that your exports occur, which may differ from the mix when the imports occur, but on average it's offsetting something similar to the average grid mix. When heating with heat pumps, the draw is heaviest at the time of least solar output (it's dark out at night- go figure!?!) which may be from fossil sources, but in Colorado wind power is increasingly picking up a larger share of the overnight load, when the average grid load is lower than the daytime load, and the fossil-burners that can are all throttled back.
The significant difference between a rooftop PV array and buying 100% renewables is the amount of grid infrastructure needed to meet peak grid loads. The absolute grid peak load in your area is still summertime air conditioning (see Table Table 2.6-5A, p108, comparing coincident winter & summertime peak totals), and distributed rooftop solar delivers that power without using the transmission grid, or even very much of the distribution grid. The details are a bit complicated (and vary by location on the grid), but in Colorado at least for the time being it's usually "greener" on many levels to install rooftop solar than it is to buy green power from remote generators located o the other side of the substation. On a lifecycle basis rooftop solar is usually cheaper too, after factoring in 30% federal income tax subsidy, even without any other local subsidies.