Water Heater - More Efficient? 40k BTU vs. 55k BTU (2023 Update)

[Dave in Denver]

My 15 year old 50 gallon gas water heater needs to be replaced (just small leak... so far).

Most all the new ones are 40k BTU. My old one was 55k BTU's.

So are the new ones just more efficient and need less gas... or do the new ones have a lower recovery rate? (can not find stats on old unit... new units have a recovery rate of aprox 40 gph.

The EF (Energy Factor) on my old unit says .55. The new ones are in the .58 to .62 range. But can that make up for a 15k BTU difference?

Maybe my old unit was a special "high recovery" model. These are still around... not to common however.

Thx Dave-in-Denver

[Rick Blaine]

Recovery rate and energy efficiency are really unrelated.

The EF is really the insulation and the damper in the flue for the non-power vented units.

Means it has a larger burner which is why the btu rating is higher.

-- "Tell me what I should do, Annie." "Stay. Here. Forever." - Life On Mars

[Dave in Denver]

Thanks Rick, Sorry I am being thick here.. are you saying if I get a new one with just 40k BTU that is will perform like my old 55k BTU?

Thx Dave-in-Denver

[hallerb]

absolutely not! the 55K BTU models are still avilable home depot locally sells them.

a 40K BTU will have a much less recovery.

the higher efficenys of today are mostly from the better foam insulation.

[nicksanspam]

Other things being equal, eg wall insulation and heat exchange surface, a gas water heater with a lower recovery rate, ie a lower heat transfer rate should be more efficient. Changing to a smaller gas orifice would likely increase efficiency.

Nick

[Joseph Meehan]

No. It will perform different. First it will take longer to recover. Of course if you don't need that fast recovery (do you ever run out of hot water?) then that would be a non-issue. It would be hard to say if you have not tried both. However if you now have a smaller family, like one or more kids away at college or now on their own, you likely don't need as high a recovery as before.

It is also possible that the lower recovery may be very slightly more energy efficient, but that would be hard to say.

[Rick Blaine]

No, what I mean is that a 40K burner will take longer to recover than a 55K burner, but that everything else being equal (ie same EF), they will use the same amount of energy.

-- "Tell me what I should do, Annie." "Stay. Here. Forever." - Life On Mars

[hallerb]

the lower recovery burner 40K or even 34K BTU aree all about producing a cheaper tank.

More expensive high BTU tanks like my PRO model have a higher purchase price, but tend to have better materials, like brass drain valves,

your bewtter off with a higher BTU tank

[Dave in Denver]

Thanks Gents!!! This just the info/advice I needed.

I want the same recovery rate that I have now so I will get what are now call "high recovery" models. And will also like the fact that these HR units are likely to have better parts.

Thx!

Dave-in-Denver

[hallerb]

if your still hot water challenged consider a 75 gallon tank, with 75K BTU, just make certain it will physically fit.

Frankly I dont know why anyone buys a small and low BTU tank.

[Rick Blaine]

For size, you have to balance your hot water requirements against energy efficiency. Sure, a larger tank is great for those times when you need a lot of hot water all at once, but you are going to be paying for that both in the initial cost as well as the increased heat loss from the larger tank.

For BTUs, I agree a larger burner is better. The problem is that they don't sell water heaters by component and going with a larger unit gets you into the cost issues listed above.

-- "Tell me what I should do, Annie." "Stay. Here. Forever." - Life On Mars

[nicksanspam]

No. Heat exchangers with smaller burners and lower heat transfer rates are more efficient.

Nick

[hallerb]

well a couple years ago I checked efficeny on a LOT of tanks, they were all within a few points of one another.

more BTUs definetely makjes for faster recovery

[nicksanspam]

It also makjes for less energy efficiency.

Nick

[hallerb]

check specs, theres very little difference

besides in winter heat lost goes to help keep building warm

[nicksanspam]

Check basic physics :-)

Nick

[Dave in Denver]

Gents, I called tech support (at Bradford White) to understand the BTU vs. efficiency thing.

Short version (all my brain could hold on to) is the efficiency numbers all take into account the BTU energy what ever that volume happens to be... so it is an apples-to-apples comparison to look just at the Recovery Efficiency (ie 79%) or the Energy Factor (ie .58) from one unit to the next (of course assuming each has the same gallon capacity).

HOWEVER... if one unit has 2" of insulation and the next unit has just 1" of insulation, and they both have the same efficiency ratings... well the 2" unit is being helped because of its R-factor so then the 1" unit would have better "blowtorch only" numbers.

Dave-in-Denver

[Dave in Denver]

What I learned (hopefully correctly)...

- BTU's do make a big difference in recovery performance.

- Efficiency numbers all take into account BTU's so it is OK to make comparison of those numbers (same gallon size however).

What I did... I picked out a High Recovery water heater that also has extra insulation and a Mag rod (not alum.).

- Has 65kBTU rather than the standard 40kBTU.

- Energy Factor, Est annual cost, first hour rating, gallon recovery.... all are higher/better than the standard water heater of same size and Mfg/model family.

Bradford White, State, AOSmith each had comparable units as expected. (OK maybe Bradford White had a slight advantage but only a lab rat with a PhD could tell the difference in the real world.)

I picked a Bradford White product for two small reasons.

1) my plumber likes and can get a better deal on B/W because of repeat business at his supplier. 2) The Bradford White has a Magnesium anode rod where the others had Aluminum... and posts I saw said the Mag rods were better.

Thanks everyone for your help! Dave-in-Denver

[nicksanspam]

It might be more efficient with the smaller burner.

Nick

[colt45gunner]

maybe the higher btu's is more efficient ? more burners to light up, but if they heat up faster, they'll run for shorter time frames every time it needs to heat up some. so, I would guess the cost to turn a 40K or 55K would be too close to be a deciding factor. So get the better recovery in case you need it !