Water heater selection strategy help

[Mattb1234]

Hello,
I've read many of the threads here related to the specifics of replacing WH's and they've been really helpful, thanks.

I'm hoping someone can help point me in the right direction for my situation.
I am looking for advice on the best strategy to take for replacing the water heaters in my duplex.
Here are some basic facts about my situation:

1. 2 br upper/ 2 br lower duplex in Milwaukee,WI. Water heaters for both units located in basement. (each unit has: the following HW demand: 1 bath room sink/shower, 1 dishwasher, 1 kitchen sink)
2. both water heaters are gas, 40gal and are nearing 20 years old
3. both water heaters vent to chimney located in center of basement (however, there appear to be 2 separate channels in the chimney -> I'll call these chute 1 and chute 2 for lack of knowledge of what they would actually be called)
4. basement is unfinished, and there's a good amount of clearance around existing WH's for flexibility on what replaces them.
5. Upper unit - chimney chute 2 is used to vent upper unit WH and upper unit furnace
6. Lower unit - chimney chute 1 is used to vent lower unit WH ONLY -> lower furnace was replaced to H.E. unit that vents to side of house.
   1. ***I believe this is a potential problem, and that a 'sleeve' was supposed to be installed in the chute to ensure the WH venting air stays hot enough to properly escape the house. It's been like this for ~3 years, no observed problems yet. although I'm not clear on what I'd observe.
7. Upper unit furnace will likely be replaced within the next 5 years, which will likely be replaced with a H.E. furnace that vents to the side of the house.

So I think I've had a good run with these water heaters, and I'd like to replace them before I find out what failure mode comes up first!

I'm curious on any options out there as to what route to go, especially related to venting methods.
here's what options I'm contemplating.

1. just replace with the same technology -> chimney vented, and install sleeve/liners if necessary
   1. probably the most straight-forward, minimal thought approach.
2. 'upgrade' both to power-vented,.
   1. allows chimney chute 1 to be sealed/insulated. Only remaining item venting to chimney would be the upper furnace.
   2. What about noise of the vent fan? anyone have experience of how loud these things are? I've read they can be really noisy, and the WH would be right under a bedroom.
   3. would need to run electrical (not a big deal in the basement)
   4. overall cost considerations
3. convert to electric models
   1. allows chimney chute 1 to be sealed/insulated. Only remaining item venting to chimney would be the upper furnace.
   2. no additional venting needed.
   3. unit costs appear similar to gas units, but running costs seem much higher. However, Does anyone know if the gas efficiency ratings take into account the amount of heat constantly venting out of the chimney(seems like this is a loophole in their calculations)?
   4. house may eventually have solar panels....so there may be a benefit/cost savings offset there.
4. on-demand /tankless systems
   1. allows chimney chute 1 to be sealed/insulated. Only remaining item venting to chimney would be the upper furnace.
   2. more efficient, but higher cost upfront,

thanks for taking the time to read all this! thanks for the help!

Matt

 

[Phog]

Hi Matt, I have a similar setup to yours -- 3 family house in Western NY. If your municipality lets you get away with it, I would suggest that you attempt to skip metal chimney liners & get new 40-gallon natural draft units similar to what you already have. This will probably be the most economical & most reliable choice. You have added a lot of details and I won't address everything here. But here is what I consider the most relevant considerations.

1. Power vent, on-demand tankless, and electric all have drawbacks. The power vent has more parts that can break down, when compared to natural draft, and will cost significantly more to install (at least the first time). The on-demand tankless units also have more potential parts to break down; will cost even more than the power vent (potentially your gas service might have to be upgraded to a larger size); and sometimes can suffer from minor usability issues such as "cold water sandwich".

And finally the electric tanks will have *very* slow recovery times -- especially with cold incoming water in the winter time in Wisconsin. It might not make enough hot water to serve a family of 3 sharing an apartment. Of these options I would only strongly recommend against electric -- the other 2 will work OK if that's what you want to go with. They will just cost more, and (possibly) be a smidge less reliable (debatably).

2. The chimney flues -- that's what you call them -- are probably OK as-is without liners. If you want to make sure, you can check for flue gas spillage near the WH draft hoods. One sign of this is plastic melting, often the blue/red plastic pieces around the cold & hot connections will show signs; or you can hold a smoking matchstick near the hood while the unit is running and see if the smoke gets sucked in properly. The gold standard would be to get a handheld CO detector and measure for any CO coming off. If you have good draft without spillage then your setup is fine.

One other thing to consider is that condensation from the flue gases is acidic & can harm clay flue liners over time. This is another advantage of installing insulated metal flue liners, besides better draft. I had a similar setup to yours, with WH vented through non-lined clay tile flue in a really old chimney (just one tank). I am in the process of taking down that chimney, which also has 2 flues, only one of which was used by the single shared WH. You can see a slight difference on the inside of the flue tiles, a tiny amount of spalling has occurred after who-knows-how-many decades due to the condensate in the one flue the WH vented into, when compared to the other flue.

The house was built in 1907 and probably has had NG water heater venting into that chimney for at least 60-70 years. I am confident I would have gotten at least another 50-75 years if i had wanted to (I'm removing the chimney for other reasons and installing metal B-vent). If you want to make sure your flues are in good shape you can hire chimney sweeps to send a video scope through the chimney and inspect everything.

The cost of installing metal chimney flue liners can be eye-opening, and completely negate the cost advantage of the natural draft units. If for whatever reason you would need to get liners, this brings the power vent / tankless options back into play.

Good luck.

 

[Sponsor]

 

[Mattb1234]

Thank you so much for the information. I think I'm going to investigate a bit regarding whether I'll should have a liner, and then hopefully just go ahead with the natural draft replacements.

 

[Dana]

The term you were looking for is indeed "flue", not "chute".

Do you live in this duplex, or is it a rental? (What you're willing to do for yourself may differ from what you'd do for a tenant.)

Search on the term "orphaned water heater", which will detail the problems than occur when venting a water heater into a ridiculously oversized masonry chimney flue. The immediate safety thing to look out for is backdrafting the draft hood, which may only occur seasonally. The longer term issue is that the mildly acidic exhaust will be condensing on the masonry, infusing it with hydrochloric acid over time, which will eventually break down the mortar in a masonry chimney. The process takes years, but rebuilding a chimney is expensive

Are the "furnaces" ducted hot air, or are they hydronic boilers (baseboards, radiators, etc)? (People sometimes use the term furnace when they mean boiler.) If the new space heating unit is a boiler, it's almost certainly oversized for the space heating load of a duplex, and an indirect fired water heater running as a zone off the boiler will increase the net operating efficiency.

If the new space heating unit is intended to be a hot air furnace, that's likely to be RIDICULOUSLY oversized for the space heating load of a duplex, and installing a right-sized hydro-air handler running off a condensing gas water heater would increase the net operating efficiency. The water heater can be either tankless or tank, but I'd personally opt for a stainless tank type condensing water heater at your wintertime incoming water temps. (The 50 gallon HTP Phoenix Light Duty with the 76,000 BTU/hr burner is a decent choice, but there are others.)

The non-condensing power vented units are noisier than tankless water heaters or condensing tanks, but in the basement it's not really an issue for any of them.

With either type of solution sealing up the abandoned flue limits it's ability to drive stack effect air infiltration for the house.

A third option (water heating only, not space heating) is to install a heat pump water heater, which will have the added benefit of dehumidifying the basement (any "musty basement smell" in summer?) They're a bit noisier than a non-condensing gas burner, but the operating costs are about 1/3 that of a standard electric tank. The recovery times are glacially slow in heat-pump-only mode, but most have a "hybrid" option, that utilizes an standard water heater element to speed up the recovery if the temperature in the tank drops TOO low.

When replacing the space heating equipment it's a once in 20 or more years opportunity moment for sizing the equipment properly for the loads. With hydronic boilers gross oversizing is an efficiency problem, not so much for hot-air, but for it can add up to COMFORT problem. Heating systems are most comfortable when they're actually running (the warm glow off the radiator, or the steady warm summer breeze out of the registers.) A rapid-cycling boiler or furnace results in temperature over/undershoots, whereas right sized units have increasingly longer duty cycles as the outdoor temperatures grow colder. A 5x oversized heating system doesn't run more than 20% of the time even during the coldest hours of the coldest days of the year.

For non-modulating systems ASHRAE recommends 1.4x oversizing factor at the 99% outside design temperature, which is enough to cover the load even during Polar Vortex events with temps reaching 10-15F cooler than the 99th percentile temperature bin, and enough to allow use of overnight setbacks. At 1.4x oversizing you'd still have a 70% "on" cycle during design-temperature weather.

If you have good records of the gas billing amounts & dates it's possible to measure the heat load bracketing the range of actual heat load using the existing heating equipment as the measuring instrument. Details on how to do that live here.

 

[Reach4]

• just replace with the same technology -> chimney vented, and install sleeve/liners if necessary
  1. probably the most straight-forward, minimal thought approach.

• 'upgrade' both to power-vented,.

The power vent has the advantage of not sending air up the chimney, or allowing backdraft air, when the WH is not heating. The problem is that air sent up the chimney gets replaced with cold dry outside air in the winter, or warm moist outside air in the summer.

The "direct vent" gets its combustion air from outside, so does not cause outside air infiltration into the house. The HTP Phoenix Light Duty that Dana pointed to is one of those.

Each has advantages and disadvantages. I have not decided which way to go if I replace my WH.

 

[WorthFlorida]

During power failures, especially after an ice storm, etc., any water heater that needs power to run fan motors and electronics will not operate. Do you have a water softener? Could explain the long life for gas fired water heaters.