Temp DHW Solution.. tell me if this is a stupid idea

bladeofanduril · November 9

Hi all. My oil-fired boiler has died and I'm looking at probably a month before I can have a replacement in and running.

I currently have an indirect hot water tank that is usually heated by the boiler. Without boiler, I have no hot water to heat the indirect.

Here is my potentially stupid idea. As a temporary solution, could I disconnect the indirect coil connections and plumb them to a small electric "point of use" water heater, with an inline circulation pump to heat the water through the coils, and theoretically heat the water in the indirect tank? I realize recycle time would be terrible, but once up to temp, I should have a 40 gal buffer. I also realize this would be creating a closed loop system, which isn't the intended usage for these heaters and I'd have to get the air out of the loop somehow.

Dumb idea? Thanks.

Jamie Hall · November 9

Not really, and recovery times may not be as bad as you might think. Not a setting for a long time usage, but you aren't planning that. You can probably use the same aquastat on the indirect tank to trigger the circulation pump, which in turn will turn on the point of use heater. Select the circulation pump so that you get close to the maximum flow through the point of use heater; you may find that a somewhat too large pump with a globe valve in line to control the flow will allow you to fiddle with that to get the best results. The size of the point of use heater selected will determine the recovery time; for a whole lot of reasons I'd be inclined to go smaller — mostly because if this is to be electric it's going to be a lot easier to wire it in.

mattmia2 · November 9

the electric water heater will be the limiting factor in the flow, the indirect will probably be 1" and the electric will be 3/4" or 1/2" depending on the model, i might be inclined to forget about trying to slow the flow down, you might eventually have flow erosion in the electric water heater but that won't be in a month. Use a circulator with a flow check and the controls on the water heater control it, the aquastat just turns the circulator on and off.

a small office restroom tank type water heater might be the least expensive way to get the package vs a tankless, the wattage of the element, the ampacity of the feeder, and the load available in your panelboard is really the only important part here.

Ironman · November 9

Why not just get a 40-50 gallon electric water heater and connect it directly to the potable lines?

bladeofanduril · November 9

https://forum.heatinghelp.com/discussion/comment/1818951#Comment_1818951

I considered it, but I'm looking for a relatively inexpensive temporary solution, rather than just switching over to electric DHW.

mattmia2 · November 9

you'll have to look closely at the cost of the circulator and the fittings to connect and be able to fill and purge and an expansion tank and a relief valve and a relay for the circulator if you need it to figure out which is the better option.

Larry Weingarten · November 9

Hi, I had a look at home despot and see less than $75 difference between a six gallon heater and a forty gallon unit. I like simple, and the bigger one certainly comes with 4500 watt elements. Input on point of use heaters is usually much less also 🫤
Yours, Larry

EBEBRATT-Ed · November 9

Just get a regular tank type electric wh and tie it in. The size depends on how much HW you can live without. A 30 gallon would be enough to get by but you can usually get a 40 at the same price.

The price of piping and circulators and it would probably cost more than a simple electric tank.

DCContrarian · November 9

https://forum.heatinghelp.com/discussion/comment/1818952#Comment_1818952

I suspect you'll find that using a full-size heater as a temporary solution is cheaper that what you're proposing, once you price all the bits and pieces. When the emergency is over you can sell it on Craigslist.

ethicalpaul · November 9

This is another reason why indirects are a bad idea—something so simple as hot water is dead if your boiler is out. And of course, why would anyone want to have to run a boiler all summer to heat a few gallons of water per day?

Switch to a resistive electric heater, or if you want to take advantage of incentives and pay a lot less per hot gallon, get a heat pump water heater.

hot_rod · November 10

you can still get solar tanks, basically an indirect with a 4500 element installed mid point in the tank. So you have a bit of DHW should the boiler fail.

A typical electric tank, 4500w is around 15,000btu/hr. You indirect could be 50, 80, 100,000 btu/hr. So recovery will be faster, typically 15- 20 minutes to recover a properly installed indirect.

Without knowing your fuel costs, operating costs are hard to predict. I pay around 13 cents per kWh, I think Jamie pays 30 cents or more?

ethicalpaul · November 10

Hot water is hard to save money with, and I say this as a heat pump water heater fan.

Even a resistive water heater uses only like $600 per year. Any savings (if there are any) from an indirect are used up on all the extra piping, circulator, heat exchanger, special tank, and labor to install and maintain it. But now I'm repeating myself!

hot_rod · November 10

sounds like he already has an indirect, he is only looking for a temporary until the boiler is fixed.

Buying a 40 gallon electric and use it to pre heat for the indirect, when the boiler is fixed. Don’t run the elements just let it warm incoming water to room temperature.

Temp DHW Solution.. tell me if this is a stupid idea

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