Help with heating DHW as well as air

[Bad LP]

If we didn’t have 7 people in the house (and before long 5 of them will be teenagers), I wouldn’t be so concerned about tankless. But as is we easily exhaust our 80gal tank (at 130 degrees) and inevitably end up with a cold shower. Never mind trying to balance that with the dishwasher and laundry washing machine.

I have all the info I need for best fit, but I still lack a link to where I can buy a lead free flow switch for <= 0.5GPM (ideally 1” fittings, but can add adapters for anything over 3/4”).

I can find a couple online, but none are verified lead free and I question their quality. Any help here would be greatly appreciated. I’m likely just not googling the right way. All I can find are paddle switches for >4 GPM (too high flow) and reed switches for 0.25-0.5GPM but <= 1/2” fittings (too small fittings).

You’ve looked on Supply House I assume? Call them as they are very helpful on the phone.

 

[sloeffle]

You couldn't pay me to own a tankless on demand water heater.

Same here. A plumber told me they cost about $75 a year just for the maintenance cost. With the OP already having a rather large family, it might be a good option for him.

Personally, I'd forgo the tankless unit and its maintenance costs and get the cheapest 80 gallon tank I could find, put a flat plate exchanger on it, and then hook a 80 gallon HPHW ( your state might have rebates for these ) in series. I have a similar setup with geo. With the price of NG and propane going up, I think you'll be money ahead in the long run.

 

[EbS-P]

tankless unit and its maintenance costs and get the cheapest 80 gallon tank I could find, put a flat plate exchanger on it, and then hook a 80 gallon HPHW ( your state might have rebates for these ) in series.

This seems like a good idea. I’d be changing out shower heads and putting timers in if you are already running out of HW with an 80 gallon. We have only done it twice with ours. Three bathtubs and load of dishes. We will be a family of 7 soon.

Got used to a single 40 gallon and for years. Kids know mom goes first ,if you want hot water plan ahead, cold= fast. I’m about to ban the kids from filling the bath tub every time they are “itchy”.

Upgrade to the 80 was nice. They hybrid mode in the HPWH get a pretty fast reheat with the top element but no better any any regular electric WH. I have read that water chemistry really affects maintenance schedule for the on demand systems.

One way I think about is since my HPWH is ducted inside and I am heating that space with wood, I am in principle heating my water with wood. Virtually maintenance free with a very simple system and getting free AC and dehumidification in the summer.

Just some thoughts.
Evan

 

[ABMax24]

There's nothing wrong with a tankless water heater, and for the OPs use case is probably a very good fit, my guess is those saying to avoid them have never used one, nevermind owned one. Maintanence on them is minor, depending on usage and most importantly water quality, they do need to have the scale flushed out of the heat exchanger periodically, I'm on a 2.5 year schedule with mine. Flushing consists of hooking a small pump up to the ports and pumping a $20 bottle of citric acid through the heater for an hour, this is a task well within grasp of many homeowners. Scale buildup can be greatly minimized by decreasing the temperature though, because it is on demand the water supply can be reduced because storage isn't necessary. 120F is a pretty common temp for tankless heaters.

If the water causes scale buildup it will happen regardless of the water heater type, a tank style will get buildup at the bottom, a plate style heat exchanger will also get buildup inside of it and require periodic flushing like a tankless.

Some tankless models also include a built in circulation pump to allow a circuit to be built in the plumbing to keep hot water very close to the fixtures. The programming of this varies, mine has the option of running every 15 minutes or a smart mode that learns our usage patterns and only has hot water ready when we typically need it.

 

[Bad LP]

There's nothing wrong with a tankless water heater, and for the OPs use case is probably a very good fit, my guess is those saying to avoid them have never used one, nevermind owned one. Maintanence on them is minor, depending on usage and most importantly water quality, they do need to have the scale flushed out of the heat exchanger periodically, I'm on a 2.5 year schedule with mine. Flushing consists of hooking a small pump up to the ports and pumping a $20 bottle of citric acid through the heater for an hour, this is a task well within grasp of many homeowners. Scale buildup can be greatly minimized by decreasing the temperature though, because it is on demand the water supply can be reduced because storage isn't necessary. 120F is a pretty common temp for tankless heaters.

If the water causes scale buildup it will happen regardless of the water heater type, a tank style will get buildup at the bottom, a plate style heat exchanger will also get buildup inside of it and require periodic flushing like a tankless.

Some tankless models also include a built in circulation pump to allow a circuit to be built in the plumbing to keep hot water very close to the fixtures. The programming of this varies, mine has the option of running every 15 minutes or a smart mode that learns our usage patterns and only has hot water ready when we typically need it.

What did you pay for the water heater? Plus Maintenance that some people can't or won't do.
A gas fired power vented heater costs ??
Both need gas to run and heat water but for how long.

Don't be to quick finding fault with wall hung on demand heaters. They couldn't come close to providing my hot water needs as my flow rate is too high for them to come close. I saw a bunch being installed in very expensive homes within a subdivision I built, some of the homes had two of them installed. That's $8000 bucks worth of "cellar wall art"!!

 

[ABMax24]

What did you pay for the water heater? Plus Maintenance that some people can't or won't do.
A gas fired power vented heater costs ??
Both need gas to run and heat water but for how long.

Don't be to quick finding fault with wall hung on demand heaters. They couldn't come close to providing my hot water needs as my flow rate is too high for them to come close. I saw a bunch being installed in very expensive homes within a subdivision I built, some of the homes had two of them installed. That's $8000 bucks worth of "cellar wall art"!!

My house came with the water heater, all new builds here come standard with them. Replacement cost on my heater is $4k Canadian.

My house and everyone else's around here runs just fine on a single 200k Btu unit. Yeah if you are going to fill 2 bathtubs at the same time you'd have a issue with low flow, but that would also completely drain many water tanks too.

 

[EbS-P]

We are within the lifetime of a new appliance of realizing substantial changes to energy cost. Increasing taxes on fossil fuels is a real possibility. Unless you have high electric cost (I’m gonna throw out a number with almost no thought) $0.25 per kWh and really low gas prices an argument could be made that putting in place electric infrastructure now is the smart money decision if you have to put in new infrastructure. You can’t buy an 80 gallon resistive water heater anymore (at least I’m pretty sure for residential installs)

Electric is the future. Efficiency and low carbon emission will be incentivize and prioritized through cost structure. A condescending gas unit will never see efficiency improvements. I suspect we will see HPWH with a COP >5 soon. EVs are really pushing the development of new refrigerants.

 

[Bad LP]

My house came with the water heater, all new builds here come standard with them. Replacement cost on my heater is $4k Canadian.

My house and everyone else's around here runs just fine on a single 200k Btu unit. Yeah if you are going to fill 2 bathtubs at the same time you'd have a issue with low flow, but that would also completely drain many water tanks too.

OK.
Your heater burns out and you need another. Do you:
A) Buy the same thing?
B) Buy a traditional gas fired heater?

You're buying gas to heat the water no matter what and that old school tank unit is $3K less. If A above; How much gas have you really saved knowing right out of the gate you're 3000.00 behind?

 

[ABMax24]

OK.
Your heater burns out and you need another. Do you:
A) Buy the same thing?
B) Buy a traditional gas fired heater?

You're buying gas to heat the water no matter what and that old school tank unit is $3K less. If A above; How much gas have you really saved knowing right out of the gate you're 3000.00 behind?

So relating this to the thread the OP is going to need 2 hot water tanks to get the capacity of 1 tankless with a large family, so the cost difference isn't quite what you make it out to be. Is there enough room to even install 2 tanks, who knows.

Is the cost exactly the same, no it's not, but there are justifiable reasons to keep a tankless as an option. There are also tankless units in the $2500 range that perform quite well, minus the recirculation pump that a hot water tank doesn't have anyway.

 

[TheNeverStill]

Thanks all for the responses. Just a point of clarification - I’ll be using the existing pump on my outdoor wood boiler as well as the water from my boiler (for the heated side of the exchanger). So the materials cost (minus personal labor, a couple adapters, and a bit of PEX) is a reasonably sized plate heat exchanger (<$500 USD) and a flow switch.

 

[Gratefulgary]

Thanks all for the responses. Just a point of clarification - I’ll be using the existing pump on my outdoor wood boiler as well as the water from my boiler (for the heated side of the exchanger). So the materials cost (minus personal labor, a couple adapters, and a bit of PEX) is a reasonably sized plate heat exchanger (<$500 USD) and a flow switch.

I know I'm a little late here...

I have a plate HX for the baseboard heat, and a Central Boiler tube-in-tube HX for the DHW. The DHW works on convection...no pump needed. One would want a tempering valve so as to avoid 175 degree water at the tap... I have an 80 gal commercial 180 degree electric water heater, and use the electric during the summer months...the cost of which is about equal to the pumps, which become unnecessary in the summer...

The system is not as simple as I have described, except for the DHW part, which could not be simpler.