Indirect with low MBH boilers?

Unknown

As I stated in the response to your e-mail to me about this, there is no need to appease me or to modify your original post.

Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.

Jim Franklin_2

No indirect DHW with low MBH boilers?

I'll be getting a Burnham Revolution RV4 with a DOE capacity of 84,000 MBH. The 53 gal Burnham indirect tank I want requires a minimum of 164,000 to meet their ratings. I spoke with a tech there and he said I'd need to get a separate water heater or live with a substantially derated tank.

Is this requirement paper-based and not reality-based? The efficiency of using an indirect tank conflicts, it seems, with its needing a large boiler to satisfy it. Also, the numbers seem geared towards needing to fill the whirlpool tub while showering and doing dishes & laundry: the first hour rating is 310 gph @ 115 degrees, which is 2x the rate of a 2.5 gpm showerhead. So with the tank derated by half using the RV4, I should still get 155 gph @ 115, no?

What gets put into large modern houses with low heat loss but high DHW requirements?

jim

jerry scharf_3

Those numbers

Jim,

You seem to have a handle on it, and the numbers are better than you think. The goal of an indirect tank manufacturer is to produce the largest possible first hour recovery numbers. This is what you call marketing. If you've got 84 MBH to give to the tank, it will heat slower.

If your 2.5 GPM shower head is running at 100F, and is mixing 45F incoming water with 120F heated water, the hot water flow is under 2GPM. That means that you could shower for 5 hours straight without running out of water. It also means that you could run a 20+ minute shower on just what's in the tank. If you have 2 showers running at the same time and they last 15 minutes each, you will still not have a problem.

If you increase the water temperature to 140F, you use less how water and the tank lasts longer still (recovery rate doesn't change.) Our resident legionella expert says it's much safer to keep the tank temp over 135. There is an increase in standby loss, but the family's health is worth it IMO.

jerry

steve b_3

Could you maintain the hot water delivery capacity using a smaller than recommended boiler output if the indirect were run at a higher than normal temperature (say, 150°F) and the output tempered to a safe temperature with a thermostatic valve? Wouldn't this essentially give the boiler more time to provide the required heat input?

Joe Brix

It all depends

on the DHW demand. Put the tank on priority and maybe add an additional storage tank to increase the dump load capacity. You can raise the set temp of the indirect up to 150 or 160 degrees and then get a tempering valve in there to mix it down so you draw off the tank slower.

Making DHW takes BTU's, no magic there. You gotta get a larger boiler or a dedicated HW maker. But like you said if your load is not that big and you can wait 20 minutes between tub fills, the indirect should be fine.

Constantin

I'd consider the following...

Most homes in the US get by just fine with a 50 or a 60 gallon gas-fired water heater. Most of these have a input rating of about 50kBTU, of which maybe 70% is put into the water. So you end up with a 50 gallon buffer tank that has a DoE output rating equivalence of about 30kBTU/hr. Yet, most families are perfectly content with such a small system. Why? Because of the buffer.

The specifications that are usually specified with indirects refer to the maximum input rating that the tank can absorb before being maxed out thermally.

With single-stage systems like all residential oil- and some gas-fired boilers in the USA, it makes sense to buy a bigger tank, not a bigger boiler if you have large dump loads like jacuzzis, waterfall showers, etc. The recovery rate will be slower than what the tank specs out as, but for most residential environments, that is perfectly OK. By going with a larger buffer, you increase your standby losses yet also increase the efficiency of the heating plant. It's a trade-off for sure.

[Edit: the rest of this post has been deleted to appease GS, see below]

Unknown

Indirect Recovery

As several folks already said here, the btuh boiler capacity listed in our I&O manual is for the maximum ratings listed. If you give the indirect substantially less, then the recovery will take longer. Twice as long......probably not. By using a 53 gallon tank versus a 40 gallon tank you already have 13 more gallons working in your favor. To add to that, the Alliance heaters are equipped with a Honeywell L4006A aquastat with a fixed 5 degree differential. Most other heaters are working with a 15 degree or more differential. This means it will respond much sooner during the draw down cycle to satisfy you needs. These heaters generally will heat up from a cold start in 20 minutes or less. Also the normal usage period for residential applications is spread over a 3 hour period. Unless you have abnormal hot water usage such as diluge shower heads and body sprays or use the shower back to back for 3-4 usages, you should be just fine.

Now....Constantin! I watched and stayed out of last weeks fiasco about your postings. I do, however, have to state that the abundance of Manufacturers, including me, that post here do not think too much of you ALWAYS jumping in to suggest someone buy another brand of equipment such as you just did once again. I respect your opinions as I do you, but constantly jumping in on these posts and pushing other equipment when people have already indicated that they have either purchased their equipment or have made a decision to do so is getting VERY old indeed. This has caused some very good people in this industry to stay away from here. Once in a while would be a normal thing but you do it in almost every post! I would suggest sharing your knowledge but cooling it somewhat with the commercials. Just my opinion of course but I'm not alone in this thinking!

Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.

Constantin

Glenn,

Allow me to disagree.

Based on your preceeding post and the e-mails you have sent me, I believe that the edited post above exactly meets your desire for me not to sway the consumer from their intended equipment choice with "commercials" for other equipment.

hr

I have an RV5

connected to an 80 gallon indirect AND a 120 gallon storage in series. This homeowner fills a large two person bathtub TWICE a day, and has plenty of time in between tubs for recovery.

That Revolution with it's intergral mixing device is well suited for long indirect calls, and cold return temperatures.

Just pray you never have to replace that underhood injection pump, as I had to do today. It is not very easy to get at when the boiler is installed in a closet, or against a wall on the back side

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

ALH_4

Tanks

Burnham Alliance tanks are the same as Crown Mega Stor tanks. They are very nice 316 stainless steel tanks with a lifetime warranty.

Half the input to the tank doesn't necessarily mean exactly half the output. Though it's probably close. Just make sure you have enough storage to handle a dump load.

People are so sensitive and easily threatened. Yes, there are better tanks, but I'd rate the Alliance/Mega Stor tanks as #2 of anything available in the US. There are definitely much worse indirect tanks.

-Andrew

Jim Franklin_2

\"Tanks\" a lot

Tons of info that confirm my suspicions about marketing ;-)

Looks like the AL53 will be fine- this place has no room for big tubs unless the 70s come around again and someone converts the livingroom into a communal bath.

Hotrod - what is this injector pump? Should I make any extra allowances to the manufacturer's clearance specs so that future servicing is made easier?

jim

Unknown

Jim

Just allow enough room from the left hand side of the boiler to be able to service the induced draft fan and internal injection circulator. Too may times this side is right up against a wall and is not accessable. This is what Hot Rod is referring to. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.