Looking for a small 95%+ boiler to DIRECTLY heat a DHW tank

Henry

None of the little wallmount units will have the capacity for the morning rush. YOu will need tons of solar panel and much more storage to provide for a 17 unit building!

kevin_in_denver_3

High efficiency Boiler for direct DHW heating

I have a 120 gallon electric hot water tank, and I'd like to turn off the elements and add a small boiler next to it.
I don't want to buy a new indirect tank mainly because of cost. I already own the 120gal. tank and it's only 3 yrs. old.

The tankless hot water heaters apparently never achieve higher than 80% efficiency, but the prices are reasonable.

I prefer to have all 120 gallons available in the morning, but I could live with a recovery rate as low as 50,000 btu/hr.

The boiler I need, then, must be rated for fresh water, and the manufacturers don't answer that question on their websites.

Is this just too odd of an application for a stainless steel condensing boiler, or does it happen all the time?

Derheatmeister

100% efficiency

The "Tankless"gas waterheaters are about 87% or just below Condensing..they are cheaper to operate but will require more maintenance i.e. a yearly flushing depending on the quality of the water that it is subjected to !

That is the reason that any "Boiler" will not allow a "Direct" interface to fresh water ,or not any manufacture that i know of.

Why do you need so much hot water?

Do you have a boiler for heat? and if so,how efficient is it? You may interface the boiler with the Waterheater via a exchanger !

You may also use a electric "tankless" like Stiebel Eltron and get 100% efficiency with no standby losses

Or maybe think about a solar Hot water system which can be interfaced with your electric waterheater

There are many ways that you may skin this cat. but using a Stainless Steel boiler directly is not a way that i will recommend doing it!

Call the guys at Low E in Denver and talk to the Hot water guys. They will be able to help! 1 800 873 3507

Hope this helps! Richard in Dillon CO

kevin_in_denver_3

high efficiency direct water heating

I'd be pretty happy with 87%, who makes that one?
I need 120gal in the morning because it's a 17 unit apt. bldg.
Looong story on why the electric water heater is there.

The existing heating boiler will be replaced by something more efficient when I can scrape the cash together. However, the water heater needs to happen ASAP.

Thanks Rich, I'll give those guys a call in the a.m.

Derheatmeister

Best in Denver

How about using a Dual coil Indirect in cojunction with you 120 gallon and interfacing it with the existing Boiler as a preheat to the 120 gallon electric waterheater ?

Like this you can reuse the tank with the new boiler which hopefully will be at 90+ effcientcy and you will be producing water at close to that eff. .You will have less Maintenance due to no extra Gasvalves/Controls/Flushing and you may even be able to interface a solar system as well? This tank may also be the best Bang for you buck, good luck.

Low E has some nice Tanks,Talk to Bob or Jack they will know as they are the best in Denver !

Robert O'Brien

Solar! Talk about perfect timing!

These guys make a pump station that includes a HX and bronze pump for this type of application.With the new tax credits in the stimulus bill and whatever CO offers it's time!

http://solarhotusa.com/residential/page19/page19.html

Check www.dsire.org for your state credis

Henry

Hot water

Simple solution for a simple problem:
Get an AO Smith BTH199 or 250 condensing hot water tank. It alone will handle eveerything at 95% efficiency. If you are worried about the morning load, you can parallel pipe it with a Grundfoss bronze circulator. I doubt you will need it!

Mark Eatherton

HTP and Lochinvar both make potable heating boilers...

Make sure you're sitting down before you read the cost...

When applying a thankless water heater, make certain it doesn't condense on you, or it too will go away. Under-sizing it in relation to the load is almost a guarantee for wet results.

Proceed with caution.

ME

tim smith

If you are looking at replacing the boiler anyway, install a

mod/con boiler on the wall big enough to heat building when you scrape the cash together to do the whole thing, install an indirect tank now and just do hot water for now. I did this on a 30 unit bldg just last spring. The customer will be doing the heat switch over this year. I know it will be more cash up front now but will be less cash down the road as you won't be doubling up on heat source. Go TT Prestige 399. Once you do your loads, that is my guess what you will end up with for that size of bldg. Stay warm, Tim

kevin_in_denver_3

n/a

kevin_in_denver_3

solar coming

Solar has been planned for a while, I have a few salvaged panels, but I still need a capable and efficient backup system.

Thanks for all the tips.

kevin_in_denver_3

historic peak load

The morning rush has been met in the past with a 75kbtuh/75 gal water heater coupled with the 120gal "buffer tank".

So, 195 gallons gets us through the peak. Normal sizing criteria would say 200kbtuh is needed, but storage capacity reduces that as we have learned.

It looks like it must be direct vent because of limited flue capacity, therefore, the AO Smith condensing tank looks best.

I have to check cost and expected lifetime though.

Steven Eayrs

why only considering a direct system?

Thats what heat exchangers are made for. Lots of condensing boiler options if you isolate the domestic water.
Also how this is piped and controled, w/ coolest returns possible, will determine if you will have an efficient condensing boiler, not some stated % rate on a brochere.
Usually to make dhw fast enough to keep up, most condensing boilers will ramp up higher for the dhw cycle, and go back down low enough to condense again for a low temp heat demand. a fair share of your dhw cycle will most likely not be low enough for condensing, unless you have a huge delta T (huge heat exchanger), and maybe even more storage than you presently have.
As some already stated, look at getting something that will be able to take over the space heating too, and save in both worlds.

kevin_in_denver_3

Money's tight

Steve,

You and Tim Smith are correct. Total system costs will be less overall if I pony up for the new 400kbtuh space heating boiler and indirect tank now.

Trouble is, it costs five figures to get there. Plus I don't really have the room for the new boiler and the old boiler.