The Tank › Should I replace old heater only for energy efficiency?
- January 14, 2011 at 11:22 am #14936
We have an old Rudd P40-7 whose energy rating seems to be at the bottom of the barrel. It’s listed here as 0.56:
It’s been installed about 12 years and works great. But with our last gas bill at $75 for the water heater, range and dryer we’re thinking it’s just consuming a large amount of gas. The range isn’t used much, and the similarly aged dryer runs about 5 loads a week. One person takes incredibly long showers.
We’re contemplating replacing the heater only to save on energy costs, but can’t find a basis or calculator online that’ll show if it’s worthwhile.
Would a new water heater or dryer really save much over time?January 14, 2011 at 12:52 pm #14937
Hello: I think that after you check out the cost of a new heater, you might want to make your present unit perform better 😎 Things to do to reduce overall water heating cost are:
1) make the equipment last
2) prevent heat loss
3) reduce hot water usage
Making it last involves maintaining the heater. You’ll see a LOT on this site about that.
Preventing heat loss means insulation (not the skinny stuff!) on all the hot lines and also the cold line at least five feet back from the heater. A thick blanket on the heater can help. Turning the temp down to 130 degrees balances heat loss with bacteria concerns. Checking the pilot flame and adjusting down (if possible) reduces that ongoing expense.
Reducing hot water usage can be as simple as low flow fixtures (suggest you look into an ultra low flow showerhead for the bather amongst you :D), or as un-simple as repiping the hot plumbing to a “structured plumbing” or manifold system depending on the house size and layout. A shower heat exchanger in that overused shower might be a good thought also as it can capture 60% of the heat going down the drain. I suppose you could try a timer in the shower, but behavioral modifications seem to be harder than repiping.
A new, water efficient washing machine that really spins out the water will make the dryer’s job much easier and use less hot to start with, so that is something to look into.
Yours, LarryJanuary 14, 2011 at 2:38 pm #14939
Thanks for the suggestions…. I think we’ve done all we can to conserve including well insulated pipes and installing water savings devices. The washing machine is a front loader that practically dries the clothes – it’s amazing.
I’ve never heard of a shower heat exchanger and studied a design diagram after googling it. Do they really work?
Wish there was a way to determine how much gas each appliance was using; I don’t know if it’s the hot water heater that’s a drain on the bill or something else.
It appears we should not scrap the seemingly energy inefficient water heater for something more economical to operate.
I found a calculator here:
which makes upgrading hardly worth the effort. Can someone knowledgeable confirm that?January 14, 2011 at 8:34 pm #14940Randy SchuylerKeymaster
One other thing to mention: you have a pre-FVIR water heater. They function with a lot less owner involvement than the current ones.
That said, at 12 years, you really need to be checking the anode. How well it works and how long it lasts are two totally different issues.
Randy SchuylerJanuary 15, 2011 at 2:21 am #14948
Hello: I’ve seen folks put a gas meter in line to their water heater. That might be what you need to do to know just how much gas it really uses… Measured results for shower heat exchangers really are 60% for the bigger units… You might measure how long you wait for hot water at various taps. Structured plumbing could help if you wait much now… You haven’t mentioned space heating. Is that not a factor in your gas bill? Put another way: is that $75 basically the same year round?
Yours, LarryJanuary 15, 2011 at 11:40 am #14951energyexpertParticipant
A 0.56 EF water heater using $60/month gets about $33.60 into the water (60 x 0.56). Upgrading to an EF of 0.80 requires buying $42 of gas (33.6/0.80). This is a savings of $18. Payback is 100 months if a 0.8 EF WH can be bought and installed for $1800. I guess the cost would be closer to $2400. But as gas prices rise payback gets quicker.
DavidJanuary 15, 2011 at 11:44 am #14952
No, the $75 is a monthly bill based on actual usage. We have oil heat and can’t wait to replace it in the spring – if there hadn’t been two full 275 gallon tanks we’d have replaced it last fall.
I peeked at the anode a few years ago and it seemed healthy. The 1800’s house has a very low basement clearance (were people shorter then?) and replacing the anode involves removing and reinstalling the heater. Even if it’s flexed.
Is there a way of calculating therm use of a gas dryer on an hourly basis, ditto for a gas range and using the gas meter reading then extrapolating gas use by the water heater?January 15, 2011 at 11:52 am #14953
energyexpert posted same time as I did.
That’s well explained and very clear. An 8 year + payback is a long time…. so I guess we’re just best off using what we have for as long as we can. I was especially concerned because the house came with a “backup” heater still which is still in the box identical to what’s installed, and we’ll someday be replacing it with that. It seems economically responsible to just use it. That owner was prepared for anything.
Thank you.January 15, 2011 at 12:39 pm #14954
Hello: One trick for knowing gas usage is to “clock” an appliance with all else off. So run the dryer for an hour and check gas meter readings before and after. Shut off other gas uses during this test. Now you only need to approximate your monthly use of the dryer to be able to calculate its gas consumption. A dryer is easier to guess hours of run time than a water heater, as you know when it starts.
Yours, LarryJanuary 16, 2011 at 10:54 pm #14966pgmrParticipant
Another issue is the distribution and service charges that the gas companies tack on to the bill. Ours is often 40% or more of the gas charge!
You need to look at just the gas usage to determine if it’s cost effective to replace an appliance.January 22, 2011 at 6:22 pm #15045
How many CF should a typical 40 gallon gas hot water heater use per day?January 23, 2011 at 8:39 pm #15053energyexpertParticipant
My Apollo 50 gallon (with a yellow sticker EF of 0.56) is listed as using 267 therms/year. A therm is 100,BTUs. One cubic foot has about 1020 BTUs. So one therm would be about 98 cubic feet. 267/365 x 98 = 71.69 cubic feet/day.
A 40 gallon probably uses slightly less.
DavidJanuary 23, 2011 at 9:30 pm #15054
So if my math is right:
(267 / 365) * 1.15 = 0.84
with gas at $1.15 per therm it’s 84 cents per day to run. Or $25month.
Perhaps with a gas range and a gas dryer our $75 monthly bill isn’t out of line.
And with the total cost of an installed high efficiency water heater it’ll have a very, very long payback time.
What’s one do to save gas energy, besides insulating pipes? The outside of the tank is not warm to the touch, so we haven’t given it a blanket.
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