Options for distant water heat - tankless vs recirculator

[narwold]

I have a situation where I'm building an addition onto my house for my parents to live with us. The addition is on one far end of the house, which makes hot water difficult. It'll be 70 feet or so just to get to the edge of the addition from the water heater, and another 30 feet from there to the farthest fixture.

Regrettably, the addition's structure is already built, and I didn't give myself enough space to add a water heater tank, because we're trying to be minimal with our requirements, and I assumed I would install a tankless heater.

As it turns out, however, tankless could be a challenge. In Ohio, the groundwater in online charts/maps that I've seen can be as low as 52°, and even the 36kw tankless units I've seen only give 4-5 (usually mid-4) gpm flow in the lower temperatures. If my parents happen to be taking a shower and running a load of laundry at the same time and someone goes to turn on the hot water at a sink, I would think it could overwhelm the system. First of all, does anyone not think that could be the case?

Next is the fact that tankless has additional complications/cost, such as upgrading my service.

I was trying to figure out if there were a way for them to share my hot water, but the distance seems to be a problem. Waiting for water presumably would be painful. I was trying to figure out if there might be a way to boost the heat at that distance without relying exclusively on heating water for the first time (stand-alone tankless).

One idea that I had was using a recirculating pump to keep warm/hot-ish water at the edge (the first 70 ft) and having a return pipe for that "trunk" portion. I was planning to run 3/4 pipe for that first 70ft and then branch off from there to my parents' fixtures. Does that seem like that could alleviate the problem sufficiently? What are people's thoughts on this?

Any other ideas?

 

[Twowaxhack]

I’d make room for a water heater on that side of the house.

 

[Twowaxhack]

At an incoming cold water temp of 50 degrees and a tank temp setting of 130 degrees and a shower temp of 105........

You’ll be using 69% hot water to take a shower.

2.5 gpm for 10minutes is 25 gallons.

69% of that will be hot water. 17.25 gallons of hot water to take a shower.

1.73 gpm of hot water delivered continuously.

 

[Twowaxhack]

You could do a series hot water heater install with your current water heater.

Install a small tank on their side of the house (20 gallons) you could get away with a 10 gallon and feed it with hot water from your existing hot water heater.

Cold water would not connect to the new small tank.

 

[RS]

A second water heater is the answer. We have a similar situation, our master bath is 70 feet from the main water heater. I installed a 2 gallon electric water heater in the crawlspace under the master bath, in series. Now we get hot water quickly, and don't notice any temperature change when using the shower.

 

[Twowaxhack]

A second water heater is the answer. We have a similar situation, our master bath is 70 feet from the main water heater. I installed a 2 gallon electric water heater in the crawlspace under the master bath, in series. Now we get hot water quickly, and don't notice any temperature change when using the shower.

70’ of 3/4” copper holds approx 1.75 gallons of water. The purge would be more.....

I like to size the secondary tank well above the required purge. The heaters seem to last a little longer.

But if it works, it works.

 

[narwold]

Thanks much! So I assume the following based on what you're saying:
- 20 gallons get pulled from tank 1 to tank 2, and tank 2 keeps them hot.
- Once the 20 gallons begin to be called for (after not using for a while), they would end up mixed with the 1.75 gallons of coldish water sitting in the pipe, followed by a replenished supply of more hot water from tank 1.
- This brief hit from the purge shouldn't make any difference in the output.

Does that sound about right? Makes perfect sense to me.

 

[Twowaxhack]

Tank 2 will be full of hot water because it will have heating elements in it and thermostats.

When hot water is called for in the addition water will flow from the smaller tank and be replenished by the larger main water heater.

Yes, the cold water sitting in the 70’ hot water line will mix in with the smaller tanks hot water and be delivered to the new addition.

 

[narwold]

Sounds good. So compared with the 2 other options:
- The recirculator would have to be running a lot to keep the water in the pipe fairly hot. Higher power consumption = not good.
- The tankless, if I went with a smaller unit in sequence with the main tank (similar to your suggestion with a second tank) - what would be the pro/con of that? (other than higher installation cost) I probably wouldn't need to have as big a unit as I was thinking if it was in sequence, so that should mean I won't have to upgrade my service.

The second tank seems like a solid option I hadn't thought of, but I still wanted to make sure I weigh against the original options.

Also the bit about 69% hot is a helpful tidbit; that means they're not using 2.5gpm hot water for shower.

 

[kiwi_outdoors]

based on our experience in a mild climate tankless are a poor choice if remotely located. In fact, we added a small electric WH unit in one bathroom to serve both wash basins (the tankless still serves the shower/bath)

 

[Twowaxhack]

Sounds good. So compared with the 2 other options:
- The recirculator would have to be running a lot to keep the water in the pipe fairly hot. Higher power consumption = not good.
- The tankless, if I went with a smaller unit in sequence with the main tank (similar to your suggestion with a second tank) - what would be the pro/con of that? (other than higher installation cost) I probably wouldn't need to have as big a unit as I was thinking if it was in sequence, so that should mean I won't have to upgrade my service.

The second tank seems like a solid option I hadn't thought of, but I still wanted to make sure I weigh against the original options.

Also the bit about 69% hot is a helpful tidbit; that means they're not using 2.5gpm hot water for shower.

I’ve never fed a tankless with a tank heater in series.

That’s backwards to me.

Goodluck with your choices

 

[Twowaxhack]

based on our experience in a mild climate tankless are a poor choice if remotely located. In fact, we added a small electric WH unit in one bathroom to serve both wash basins (the tankless still serves the shower/bath)

Any water heater remotely located without circulation is a poor choice. It’ll make you wait. How long you wait depends on how far the heater is away, how much water you’re flowing to purge and what size pipe delivers the hot water.

 

[kiwi_outdoors]

speaking of not wanting to wait for (gas) Tankless hot water to arrive hot at our kitchen sink, we are finally installing a small 2.5 Gallon Rheem electric tank in the blind space at the corner of the kitchen cabinets. Access will be by an exterior door in the stucco wall. We will use anRV baggge door - its weathertight and insulated. For a retired couple - it will be sufficient. It will be fed by cold water.

IF its not quite enough HW cabpacity, we can feed it from the Tankless HW source.

 

[Mitchell-DIY-Guy]

Any water heater remotely located without circulation is a poor choice. It’ll make you wait. How long you wait depends on how far the heater is away, how much water you’re flowing…

EXACTLY! IT AIN’T ROCKET SCIENCE!
But still, it’s exceedingly rare when a builder or plumber actually gives this a moment of consideration for the benefit of the homeowners who will spend decades in their home. Plumbing for a return line or other schemes is super easy and cheap when the homes initial plumbing is installed, nearly impossible when the walls are up. You should have heard the excuses the builder and plumber gave me when I was trying to build a new home in 2019. Made me think both were in the wrong business…