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wetling
Tankless hot water heater advice
wetling

I live in Denver and have two average showers, an average dishwasher, and an average clothing washing machine (in a two-story house). My wife and two elementary-school kids are currently using a 15-year old tank water heater and would like to replace it.

The existing heater is in the basement and sits on the floor near an exterior wall. It is powered by natural gas, so there is some venting in-place.

I have been looking at Home Depot and Amazon, and I'm just not sure if I can get away with a tankless water heater with my budget. I wonder if a water heater like one of the following would work well for me.

https://www.amazon.com/dp/B002635ODW/ref=wl_it_dp_o_pC_nS_ttl?d_encoding=UTF8&colid=1UJS3REDAJ70P&coliid=I3IBDL5ZKE90CV

https://www.amazon.com/dp/B003QSENZ6/ref=wl_it_dp_o_pd_S_ttl?_encoding=UTF8&colid=1UJS3REDAJ70P&coliid=I3SF5EW2Y3TXBL&psc=1

https://www.amazon.com/dp/B003QSGIAY/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=1UJS3REDAJ70P&coliid=I26XVNF9XXBAFA&psc=1

As you can see, I am looking at electric, but should I be sticking with natural gas (I think I have space in my breaker box, for additional breakers and will verify soon)? Are these example water heaters reasonable, or do I need to go up in price, given that I expect to keep the water temp at 120F? What am I not taking into consideration?

Thanks.

keith3267
Re: Tankless hot water heater advice
keith3267

"What am I not taking into consideration?"

You are not taking into consideration the size of the transformer that supplies your house. You need to determine if the transformer is large enough to handle the 80 to 120 amps that the tankless water heater draws. Do not be confused by the size of the circuit breaker panel. You may have a 200 amp service panel, but that does not mean that you can get 200 amps continuously to your house. The transformer determines this.

You may have a single transformer that supplies only your house. This is typical in rural areas. Typically these transformers are 15 kVA which can supply 62.5 amps continuously. They can supply up to 4 times that for very short periods of time, but once the rated capacity is exceeded, the voltage drops. You may notice this from time to time when a major appliance kicks on and your lights dim slightly. When one of these kicks on, you will really see your lights dim dramatically.

Two of these units are over twice the capacity of a 15 kVA transformer and one of them is at 128% of capacity. The 19.2 kW unit may be OK as long as you don't turn on the oven or the AC unit.

You could ask your power company for a larger transformer, but this is a big expense for them. A larger transformer would cost them $1000-1300 just to buy it, then they have to pay the linemen to install it. It doesn't stop there either as all transformers draw some power just to stay alive, even when nothing is on at your house. These are called no load losses or iron losses. A modern 15 kVA transformer draws between 25 to 50 watts of no load losses, thats 24/7 and because it is before your meter, the power company eats the losses. A 37.5 kVA which you would need will draw from 40 to 80 watts, 24/7.

Transformers also have load losses caused by the internal resistance of the windings. These losses vary with the load that is being drawn. Load is another term for amps when the amps are being used to power something as opposed to amps that are being supplied or are just flowing through a wire on the way to the consumer.

Load losses at 100% rated capacity typically are about 1 to 2% of the power being consumed at the time. But load losses go up exponentially as the load exceeds the rated capacity. At 150% rated, load losses can be 2 to 3 times higher than they were at 100%. You are asking for 200+%.

If you are in a suburban or urban environment, it is likely that you will be sharing a transformer with your neighbors. This is especially true if you have underground power lines. If you have underground power lines, up to 8 homes may be sharing one 75 to 100 kVA transformer. As long as you are the only one with an electric on demand water heater, there should not be any issues. But if you start bragging about how much you love your on demand and all your neighbors run out and get one, there will be trouble.

You could stay with gas, but there is the possibility that your gas line may have to be replaced, or a separate gas line run. These use a lot of gas so in the winter, if it and your house heater both kick on, the gas line pressure could drop too low and both shut off. In the end, the gas would be the better choice though even if you need a new gas line.

However, a tankless may promise savings over an old tank type, the savings won't be that great compared to a new tank type. The new tank types are much more efficient and have better insulation. Tank or tankless, it costs the same to heat the water. The savings come only from the storage of hot water. New tank type water heaters cut the heat loss from storage to between 1/6th and 1/10th of what the older water heater you are going to replace, so I'm afraid after all the expense of switching over to tankless, you will be very disappointed in the savings.

One last thing, going from a gas fired tank type to an electric tankless is going to increase your hot water costs, there will not be any savings.

HoustonRemodeler
Re: Tankless hot water heater advice
HoustonRemodeler

The few electric on demands we have installed were all removed in less than a year of their lives. Between the spike in energy affecting other electronics in the house (and neighborhood in one case) the units just couldn't keep up with the demand.

Gas on demands are great but require 1 inch gas piping and larger stainless steel exhaust. The exhaust is usually the more expensive part of the equation.

bill
Re: Tankless hot water heater advice
bill

I am not a fan of instant hot water tanks at all. and here is why
1) they can only supply hot water at a certain capacity ie 1-2 gallons a minute. than means that the showers are very low volume. and if you want to run the dishwasher, clothes washer at the same time you can not. now picture
monday morning. you want a shower, you son wants to wash his hands, and your wife wants to wash the dishes.
you cant .
2) the cost is more than a regular hot water tank.
3) parts burn out and have to be replaced aND COST A LOT.

Bill

wetling
Re: Tankless hot water heater advice
wetling

Y'all have convinced me to stick with a regular, old tank. Thanks.

HoustonRemodeler
Re: Tankless hot water heater advice
HoustonRemodeler

I'll disagree on the low output. We volunteered to build a bathroom facility at a campground that goes from being empty during the week to having 200 people for the weekend. Tankless LP was the way to go. People shower all day long, as long and as frequently as they want while other people shower, flush terlits and use the sinks. This particular bath house has 3 shower, 4 terlits, 3 sinks. No one complains of not enough hot water. We did install a pressure balancing loops to compensate for multiple users.

The Rheem LP on demand has been purring along nicely for the last 4 or 5 years.

Fencepost
Re: Tankless hot water heater advice
Fencepost

Another factor to consider is the cost of supporting infrastructure.

If you're just replacing an existing gas (or electric) naturally vented tank-style water heater with a comparable gas (or electric) water heater, then your only purchase cost is the water heater and maybe a few incidental fittings.

If you go from one type (tank or on-demand) or fuel source (gas, electric, oil) to another type or fuel source, you not only have the water heater purchase price, but you also have to remodel the supporting infrastructure. This may mean that you'll need to change out the gas supply line, the exhaust system, or the supply wiring. That infrastructure can easily cost more than the water heater itself.

* * * * *

Then there is a more philosophical consideration: the utility infrastructure of the community.

Electrical and gas distribution systems have to be designed for peak load. Since on-demand water heaters have a higher peak load than tank-style water heaters, if a large number of homeowners change to on-demand heaters, the utilities will need to upgrade their facilities just as you have to upgrade yours. (When everyone is taking showers in the morning and turning up their thermostats, utilities already see a demand spike. On-demand heaters will magnify this spike.) At some point, this will mean drilling more natural gas or oil wells; building more pipelines; building more power plants; stringing more high-tension, high-voltage power lines across the countryside; and tearing up neighborhoods to replace aging, undersized gas lines just to support the higher peak demand, even if the demand over time is reduced.

So while the overall efficiency of tankless heaters may be better, they aren't necessarily better for the environment or the budget. Instead of averaging the load as tank-style heaters do, they create spikes and dips in demand. In order to pay for the upgrades to handle those wider swings, utility rates will rise.

Efficiency is a wonderful thing, until the efficiency comes at the cost of the environment and finances in different, unexpected ways.

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