2 vs 1 hot water tanks

[bagofpucks]

Hey CP house experts I need your advice. We currently have two 40 gallon hot water tanks, but one has kicked the bucket, so it’s time to look for a replacement. My HVAC guy recommends going to a single 75 gallon tank. I know that’s what was originally in the house, but the previous owners moved to two tanks when the original died. We have hydronic in floor heat on the basement, so we do use a fair amount of hot water. Tankless is not an option as we live on an acreage with well water. Any hot water tank experts can weigh in? Also, any recommendations for manufacturers/installers?

[calgarygeologist]

I don't know how true it is but I have heard a few times that larger single tanks are not as efficient as smaller tanks.

Any chance you could convert your infloor system to a geothermal heat pump and move to a single tank? Might be a significant investment upfront but beneficial in the long term.

[GoinAllTheWay]

6 of one, half a dozen of the other IMO. Both cases have pros and cons although pretty minor I'd wager.

1 large idle tank is going to lose less heat than 2 smaller ones, that's really the only "bigger" difference I can think of.

As for the right now, you have plumbing in place for 2 tanks. Moving to one is likely going to require a bit more work so bigger bill.

**edit**

Here's another thought, you could possibly have some redundancy with a 2 tank system. If one dies, you could possibly rely on the other, depending on how your plumbing is set up. Handy as it sounds as though you are remote and help may not be as quick to arrive compared to living in the city.

[bagofpucks]

Yes, good point, and that’s what we’re doing now as one tank still works and we don’t use a ton of hot water in the summer. Alternatively, you could argue two tanks is twice the maintenance and twice the stuff that could fail. Thanks for your thoughts!

[Lumby Lager]

Have you looked into switching over to a closed glycol system for your heat and just one hot water tank?

[DeluxeMoustache]

About the heat loss, how much of an issue is that, actually?

Most of the year, Calgarians heat their houses. Heat “lost” by the water tank is lost to the air surrounding the tank, which is in the interior of the house, which is usually insulated

Isn’t it just less kJ for the furnace to make up, in terms of an overall heat balance?

[Samonadreau]

Originally Posted by DeluxeMoustache

About the heat loss, how much of an issue is that, actually?

Most of the year, Calgarians heat their houses. Heat “lost” by the water tank is lost to the air surrounding the tank, which is in the interior of the house, which is usually insulated

Isn’t it just less kJ for the furnace to make up, in terms of an overall heat balance?

Technically true but almost as inefficient as heating your house with a light bulb.

[DeluxeMoustache]

Originally Posted by Samonadreau

Technically true but almost as inefficient as heating your house with a light bulb.

Sure, and so when you pose the question when talking about heat loss from water tanks, if it is really an issue, can we actually say if is even a factor at all, for practical purposes?

[bizaro86]

Originally Posted by Samonadreau

Technically true but almost as inefficient as heating your house with a light bulb.

Can your explain why that would be the case?

Energy is conserved. The hot water tank burns natural gas, which is the same fuel as the furnace. The chemical energy released by burning the gas seems like it would all be converted to heat (maybe small amounts to light/sound, but inconsequential and likely the same as the furnace).

That heat is either going in the water (good), out with the flue gases (wasted to outside) or into the house (offsetting furnace usage). It seems that wasted to flue gases should be comparable to your furnace (depending on efficiency).

Heating with light bulbs seems stupid because they only use small amounts of energy and electricity is more expensive than natural gas. I dont think waste heat from a hot water tank has many of those disadvantages, and I wouldn't factor waste heat into my decision (assuming the tank is in an insulated space inside the house).

Basically, it is so inconsequential that it doesnt matter for this decision, imo.

[photon]

Incandescent light bulbs are very efficient heaters, only about 5% of the energy gets converted to light. And the light gets converted to heat after bouncing off enough things and stays in the house unless it goes out a window. The other 95% is output as heat.