Gas condensing or tankless replacement


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Old 09-15-18, 10:21 AM
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Gas condensing or tankless replacement

To set the stage......we bought a house recently and it has a direct vent 50 gallon NG storage tank water heater in it. The tank is 25 years old. I'm shocked it still work. So in being proactive we are looking at replacing it. As you can see, there isn't much clearance above the tank.

We'd like to do something is high efficiency even if it costs more. So we've looked at tankless and condensing storage tank units. So far I've been unable to get anyone to tell me what a condensing storage unit would cost to install or even agree to install one. They all only seem to want to do a direct replacement (which of course isn't very energy efficient) or tankless. One person I had out said there is no way to tankless as the the gas line isn't big enough but he didn't do any pressure measurements or anything for the gas there. He just looked at the gas pipe and said "too small." The one person that did give me a quote on a tankless was saying about $5-$6k to install. A direct replacement is around $1700.

Anyway, I'm looking for some guidance from the brilliant people on here on what I should do going forward. I don't really want to just put in another direct vent low efficiency unit.

I'm capable of doing the work myself with some basic things like the plumbing and what not, but wanted to get your alls take on what makes the most sense.
 
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Old 09-15-18, 11:07 AM
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I'm not the pro in this forum just speaking from experience. I remember when the tankless water heaters were introduced. They were touted as the next best thing to sliced bread. The idea is fantastic but the application has problems.

I know people..... friends and customers.... that use them. They are either fairly reliable or nothing but trouble. The problems seem to be heavily dependent on the mineral content in the water. They do require a large volume of gas instantaneously so a survey will need to be taken of the gas piping to see what it needs to be upsized to. The supply from a standard water heater will typically not be large enough.
 
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Old 09-15-18, 12:19 PM
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Thanks. I've heard many mixed things as well What I'm trying to figure out in a sense as well is why.no one will quote me the install of a condensing unit. My existing gas line would work we would just have to out in space for combustion and venting air and then put in a condensate pump. Seems pretty straight forward no?
 
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Old 09-15-18, 01:01 PM
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Pick a unit you are interested in. It will tell you how many cubic feet of gas is required. It should state whether or not a condensate pump can be used as the condensate could be hot.
 
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Old 09-16-18, 09:40 PM
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It would actually be pretty easy to see that the gas piping is undersized, assuming low pressure gas. If it was supplying a tank water heater, it will almost certainly be undersized. Tankless water heater gas requirements are much higher than tank waters heater -- approx 4 times as much -- and it's not unusual to have to run piping all the way back to the meter to satisfy that demand.

A few years ago I was on the tankless bandwagon, but they are so expensive to install (your existing vent won't work either) and the return on investment is so long, that you really have to need endless hot water make it worthwhile, imho.
 
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Old 09-16-18, 10:27 PM
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Yeah we're also just thinking about the green part of usingess NG.

But I am still thinking a condensing storage tank might be a good option for us. A little higher up front cost but a lot more efficient.

We've also thought about going to an ectric storage tank since WA is almost all hydroelectric, we're a little more OK with that, but I'm not thrilled with the cost to run that system.
 
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Old 09-17-18, 01:06 AM
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Depending on the cost per KwH, NG is usually cheaper than electric. Almost always unless you live next to the Hoover dam.

It is reasonable to be concerned with efficiency and environmental considerations, but the sad fact is that a condensing storage tank will have more do-dads to go wrong inside.
I would take a good look at the warrantee.

For plain & simple hot water, it's hard to beat the tank. Efficiency can be made up in other ways, like low-flow shower heads and being mindful of hot water usage. Solar hot water (depending on where you live) is also worth looking in to. Solar panels might offset the cost of running an electric water heater.
 
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Old 09-17-18, 08:28 AM
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If you have a hot water boiler for heating your house, an indirect HW tank can be a simple, effective, and efficient solution.
 
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Old 09-17-18, 09:01 AM
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Unfortunately, we live in the pacific northwest so sun isn't usually on our side :-)
 
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Old 09-17-18, 09:41 AM
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If you have a hot water boiler for heating your house, an indirect HW tank can be a simple, effective, and efficient solution.
We indeed have a boiler for heating. Forgive my ignorance since I know nothing about them, but are they a lot more efficient than a standard tanked heater.

At our old house we had a powered vent gas storage tank. it seemed pretty efficient and had no condensate. Maybe that is an option too. Too many variables. LOL
 
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Old 09-17-18, 12:28 PM
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I can't quote any efficiency numbers but from my own experience and what I have read in the DIY forums and elsewhere, an indirect heater is more efficient than a stand alone water heater. I can tell you that the amount of hot water available and the recovery rate are certainly better.

Boilers are more responsive than stand alone heaters because of the amount of water that is being heated. Heating 3 to 4 gallons (in a newer atmospheric) cast iron boiler to 150 to 180 degrees takes about 5 minutes and the heat is transferred to the hot water tank quickly due to pumping. Heating 30 to 50 gallons of water in a stand alone tank will take about 30 minutes and will usually not keep up with the demand.

I have my boiler set for 150 degrees and my water tank set for 120.

An added bonus: I am on a gas heating rate that remains in effect even in non-heating months. My hot water, cooking and clothes drying cost is at least half of what it was on a standard residential rate before I converted to gas heat.

Indirect water heater tanks are stainless steel with SS heat exchanger and do not deteriorate like a coated steel tank.
 
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Old 09-17-18, 12:32 PM
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Do they make retrofit systems? Our boiler is about 25 years old as well but the advice we've gotten is that it's still pretty good and doesn't need to be replaced.
 
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Old 09-17-18, 09:32 PM
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It should be possible to add/replace a zone to an indirect tank.

Here's an interesting solar map though:

https://globalsolaratlas.info/?c=39....14,-127.448616
 
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Old 09-17-18, 09:42 PM
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It should be possible to add/replace a zone to an indirect tank.
As it turns out, our utility company is also offering an $800 rebate if you put in a high efficiency boiler and indirect hot water storage tank. Couple that with the $1800 for a new storage hot water tank or even more to go high efficiency and it starts to maybe make sense to swap the whole system out
 
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Old 09-18-18, 07:52 AM
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Run the numbers. What would be the cost for a whole new setup after the rebate? Check to see if there is a rebate for adding indirect HW only.

Gas savings will not offset the cost of the new high efficiency boiler and they are harder to maintain and don't last as long as atmospheric boilers.

$1800 to add an indirect tank with pumps and controls sounds reasonable.
 
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Old 09-18-18, 08:10 AM
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Run the numbers. What would be the cost for a whole new setup after the rebate? Check to see if there is a rebate for adding indirect HW only.

Gas savings will not offset the cost of the new high efficiency boiler and they are harder to maintain and don't last as long as atmospheric boilers.

$1800 to add an indirect tank with pumps and controls sounds reasonable.
We need to get someone out to give us an estimate on a complete system. We don't have that yet to run the numbers. Also, since we just moved into the house, I don't really have historical numbers to run against for total gas usage.

The $1800 was for a standard direct vent storage tank. I'm looking around to see if I can get someone to do it for less.

I also want to find out about just adding the indirect onto our existing boiler. So I need to gather more data on that front. I think the indirect is a better way to go thank tankless in our situation. The question is, is it better than other options, and I think it probably is given our constricted space and desire for higher efficiency. This may be one of the few times I'm glad we have a boiler.
 
 

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