Mod-con choices for small heating needs

hr

I think it is all about the surface area of the heat exchanger, regardless of it being an indirect or reverse indirect.

My experience with the large surface area tanks seems to agree with that.

In that category I look at the reverse types with hundreds of feet of copper coil, and the tank in tank style where the whole tank surface comes into contact.

Viessmann also has a lot of large diameter coil in some of their tanks for strong performance.

Having two pumped flows really increases heat transfer also. A recirc pump on the domestic would move water across the coils better but you lose stratification in the tank, a trade off of sorts.

I've also noticed the small finned coil tanks suffer most from high mineral content water and their performance drops quickly.

I did have an Ergomax drop to almost zero DHW production this winter. The tank was installed as a buffer to a Clean Burn waste oil 350K boiler.

The problem arose due to the fact I only had a couple hand sinks as the DHW load. I believe the low flow, and related low velocity caused those small tubes to plug up. And extremely hard above 20 grains water!

I cut the DHW connection at the bottom and sure enough the three 1/2" copper coils were almost completely plugged. Opening a sink faucet would provide one quick burst then drop to a trickle. At first I thought it was in the 3 way thermostatic valve, but found the real problem when I started cutting.

Just some comments to be aware of. Low hardness water and high flow rates would no doubt eliminate that sort of a problem.

hot rod

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Gene Davis_2

Less than 36K Btu/h

Small new house, modest heat loss, what might be our LP-fired mod-con choices for a total heat loss under 36K, DHW not included?

ttekushan_3

Add the DHW

and use a Triangle Tube Prestige 110. It mounts on the wall, easy to set up.

Mad Dog_2

They are all good choices...the major brands I mean, but

The problem right now is that even at their lowest turndown ratio, they are often oversized, Several here have been prodding the manufacturers to put out a machine that maxxes out around 50k and can wind down to less than 10K. I'm sure one of them will get it done soon. I hope. Hey, even the tankless water heaters turn down to around 15 K. We would all love to see a mod/con that could achieve that. Mad dog

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Brad White

You are not alone, Gene

Mad Dog is right, we would all like smaller ModCons.

I am designing a spec house for a friend now, with a heat loss of just under 50K including heating the basement, in RI.

Being a spec house much as I believe yours is, first cost is always a liability especially in this unstable RE market.

Best fit in the market would be a Munchkin T-50 or 80 with DHW boost but we want to wait until the blower issues settle. I think alot of us wish that line would be the boiler it could be, for it falls into a nice niche size and price point. Minimum turndown for the 50 and 80 are 18K and 19K respectively. I do not mean to bash a product, HTP has a good line, just some issues that give me pause on the boiler side.

Beyond that my choices would be a Viessmann Vitodens with Buderus GB-142 or Triangle Tube Prestige 110 as equal second choices. The turndown minimum inputs are 25, 25.3 and 30 MBH respectively.

The approach I am suggesting for our project is to have the boiler be a "plug in" and price all three then give the eventual owner a "features and benefits" package with upgrade price list. The distribution will be panel radiators with PAP homeruns and TRV's, by the way. Some radiant in baths and kitchens, maybe a radiant-ready basement.

On a house such as this, the boiler will cycle/pulse (go into on-off or bang-bang mode) when the OA temperature is over 32. Sometimes you have to admit defeat. What gnaws at us is the worry that a "killer ap" ModCon with a 50 MBH input and 5:1 turndown will be on the market moments after completion

Brad White_9

another

Weil-McLain Ultra 80 goes down to 16k input, although it has a time maintaining stable flame under certain conditions at that rate.

A buffer tank is probably your solution to low load.

Ken_40

I still consider the Munchkin line from

HTP to be the best bang for the buck out there.

Remember too, if you buy a 50,000 BTU mod-con boiler, you will need substantially sized indirect water heater. It takes 100,000 BTU's (without any storage capacity) to take a shower with a 3GPM shower head. There is a direct relationship as to how much D/H/W you can draw per minute, the BTU output of the boiler - and the amount of storage required to deliver whatever may be required.

You said, "Without D/H/W" - why? Is there no domestic hot water in this app.?

Brad White_9

I suspect

the "no DHW" term was to state that the heating was a net load exclusive of DHW, Ken, just to illustrate the normal heating-only requirements.

Perhaps off line, Ken, you could tell me about your Munchkin experience. You seem to be a fan and not to have had the issues others have experienced (exclusive of not following instructions of course!). Not a challenge for I have no experience one way or the other; all I know on them is second-hand.

Brad

D107

you probably know Clammy does loads of Munchkins

I don't think he'd mind me repeating his comment that he wasn't entirely pleased with the DHW indirect recovery of the smallest 50K model. That might be the only drawback of any mini-mod cons that emerge--but then perhaps the indirect can just be sized X% larger. Or perhaps a reverse indirect can be used, which has a quicker recovery. (I'm thinking specifically of a Turbomax, which Mark Eatherton has posted favorably about.)

David

hr

Plenty of 11 and 13 KW units were at ISH

The Giannoni booth had a wall covered with small output mod con HXers.

I agree with Ken, if DHW production is expected I doubt many would be pleased with under 50K sized units.

I'm not sure the reverse indirects would work any better. A btu is a btu, they can't be amplified by reversing the indirect. Remembering a post where Mike Gordon called Jean of Ergomax out on those "higher efficiency" claims

hot rod

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Ken_40

I was unaware of Clammy's lean to Munchkin.

But that's understandable.

I do not understand how anyone can have "issues" with D/H/W and boiler sizing. It is NOT a function of boiler BTU output that determines the adequacy of D/H/W volume. It is a function of SIZING the indirect properly!

Hell, we've had homes with 34,000 BTU INPUT (about 22,000 OUTPUT) in a 40-gallon water heater for 50-years and never ran out, how can we suggest a 48,000 BTU OUTPUT boiler and 40-gallon indirect can't?

Perhaps water temperatures are an issue, mixing valves a requirement, boiler water temps and issue, D/H/W priority missing, but unless you have 6 teen age girls in three simultaneously running showers and a hot tub fill happening all at once, the math is certain; YOU WILL HAVE ADEQUATE HOT WATER!

There are always extenutaing circumstances, like a very large family or home with 5GPM shower heads. I doubt if a 50,000 BTU mod con would heat the house in that instance but assuming it did - PUT IN A 60-GALLON INDIRECT!

Boiler output is interesting, indirect water storage sizing is EVERYTHING!

Why the Munchkin? Stainless HX, cost, factory support, made in the US, parts easy to get, warranty, controls options, did I mention cost? Small footprint, wall mount options, weight, extreme venting possibilities/option, did I mention price? Simple operation, lots of non-exotic (meaning most parts are not proprietary) and if a part is required, the local wholesaler would stock a replacement, phone factory support, although rarely needed, easy to reach, did I mention cost?

Other than those things. They're nothin'special(;-o)

hr

dp

Mad Dog_2

I agree Ken, I'm just curious as to why he wants to leave out

the indirect...is it lack of floor space? Mad Dog

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[Deleted User]

Real life experiences...

I live with a 50 K modcon, tied to an 80 gallon reverse indirect, and so long as only one point of use is running, I can NOT run it out of hot water under normal usage. I did during testing, but it took 2 hours to draw the tank below acceptable temperatures.

And, the LLA takes a nightly bath (standard 5 footer) and she now has the system "dialed in".

I agree with Ken (SHOCK!!), there are a LOT of inefficient tank style water heaters out there taking care of the needs of hot water for families a lot bigger than mine. I suspect thermal constipation as the reason that Clammy is not happy with the performance of side arms tied to 50K modconners.

It goes back to the American way of life. Put in a big tank with a small heat exchanger and crank the boiler to 180 degrees and stand back and hope for the best. With a good reverse indirect HXer/storage tank unit, you typically don't need a tank set point that is more than 10 degrees F higher than your required output temperature, and the heat source stays right in its "sweet spot" of efficient operation.

Time to quit thinking cheap and start thinking efficiency that can justify the additional expense. THe only real need for stored volume would be an exceptionally large dump load (i.e. 1 man, 7 woman Olympic swimming pool size Jacuzzi hot tub). In most cases, the chances of having to satisfy parallel showering events are slim to none, but need to be taken into consideration (ski resort chalets).


If the showering times can be managed into a back to back situation, the tanks size comes down to a reasonable size.

My 80 is probably oversized, but the price was right (Thanks Amtrol, Greg and Steve!!) and I am extremely happy with its performance to date. Unfortunately, it's not currently available on the open market...

Wake up American tank manufacturers, if you build it, they will come... I have. (Don't even try to turn this into an inuendo...)

ME

hr

defining the DHW load is the trick

most people "assume" and indicate they use a lot less DHW than they really do.

I would say in many cases the DHW load will exceed the heat load in new, well insulated homes.

Large tubs, and expected fill times will be your un-doing

hot rod

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Gene Davis_2

Let me try to rephrase the question

Heat loss for house is 36K btu/h at design temp. House has two full baths, each equipped with a tub/shower, no whirlpools. Kitchen has a dishwasher.

Worst case situation for DHW is that two people want to fill the tubs for baths, not showers. Someone wants to do a load of dishes at the same time. I guess that is about the worst case.

So my question is now, which boiler choices might I have for this, and what size Superstore tank for DHW might we want?

We would like not to be short cycling in the heating mode.

Ken_40

Wow Try this one...

What are the odds that two people will draw a bath within 5 minutes of each other - AND the dishwasher will take more than 2 gallons of straight hot?

Almost as long as "What if someone leaves a window open on a day when it's 11 below zero and the wind is howling at 40 MPH? Sure, it COULD HAPPEN, but really...

If this family does have the scenario as more than just three days a year, you must design for it, agreed. And, if that were the design basis, I'd use a 50,000BTU mod-con (pehaps the one that HTP makes that has 80k "reserve firing rate for this very situation we explore - and use a 60-gallon indirect!

DONE. If the extreme you cite is a rare thing indeed, use a 40-gallon. I'd bet lunch you'd never beat it anyhow.

Noel

Pretty easy

You may reconsider filling both tubs at the same time.

Measure the gallons that both tubs hold. Buy that many gallons of indirect water heater.

Size the boiler to the house heating load.

There isn't a system out there that will allow you to MAKE the water hot as you use it at that rate, and still be efficient at house heating.

Do you want the corvette performance, or do you want the camry economy? Pick one....

D107

some reverse indirect numbers

Hot Rod I don't know about Ergomax--which some wallies have said used to be under-insulated--but just to throw out some Turbomax numbers and see how they strike you:

The smallest size T23, volume is 26 gal, heat transfar area is about 20 sqft, utility and boiler connections 1.25"NPTM, it's 49"H x 18"D and at 50Kbtu net first hour produces 71 gallons at 140 deg. Continuous produces 60 gallons. All 100 deg rise, boiler water 180deg. (I assume when they say net here they really mean DOE gross output in terms of boiler, since there's no pickup.) If the 140 deg water is mixed down to 120, then the DHW output figures jump a bit. (Standby loss .5 deg/hr.)

These SEEM like better numbers than the standard indirects I've seen, plus less cleanout concerns since main tank is inert boiler water; potable goes through copper tubing. plus if need be it can be used as a buffer.

Thanks,

David

Glenn Sossin_2

Munchkin all good things but

A issues I've come across
I've heard the electronics are overly sensitive to electrical noise. Have heard of contractors still using them because of your points, but makin the power supply to run the boiler a computer UPS . Ever come arcoss that?

Second, harder to purge because of helical design of the heat exchanger. Also very sensitive to correct piping methods. Not all plumbers out there are of the caliper we see here.

We were going to bring on the line and then backed off after we started looking deeper. Looked like to many potential issues. Took on the Prestige instead - very happy with that.

Ken_40

Not having any experiences with the

Prestige, I cannot compare apples to apples, however, all mod-cons rerquire P/S piping IMO and that alone takes most installers we all know dominate this biz, out of the equation.

If you do not devour the instructions BEFORE the install, there will be issues. I can only tell you of my experience. I have never had any issues with electronics or power supplies, so have no comment of that issue. That's the first I ever heard of that one.

The pressure differential accross the helical HX (which BTW is the way most make 'em, - not just HTP) will not "allow" air entrapment, unless someone doesn't understand how to do P/S, which in and of itself is a deal breaker for any mod-con I can think of.

I also like Viessmann and W/M. But bang for the buck, with quality as a very close second consideration, nothing comes close to the Munchkin in my book. This, while admitting I have not seen the Prestige, only good things about it.

Remember, the Munchie has been out for well over 5 years, closer to 10. How long has the Prsetige been out? And rhetorically, if bad things happen to them after a year or two, how would we know it?

What is the country of origin BTW? Is it Yank?

Glenn Sossin_2

Not all

Dunkirk and Prestige have low head losses through exchanger which would allow for potential use of convention circs like a UPS15-58FR. Infact, the Prestige 110 comes the circ built in. Check out this attachment.

ALH_4

Tank vs. Tub Temperature

I would plan to run the water heater hotter than the tub temperature. 120 gallon water heater at 150°F should deliver approx 170 gallons of 105°F water at the tap assuming the boiler is not firing into the tank while they are drawing hot water.

Glenn Sossin_2

prevent cycling

bigger storage/indirect tank

Glenn Sossin_2

agree -DHW Load can be larger

Find this to be true especially on larger custom built homes. Frequently told - I don't want to run out of hot water - period.

Wayco Wayne_2

Prestige

is from Belgium in response to Kens query. I was fortunate enough to visit the Prestige factory in Belgium last April. We got to ask the CEO of the manufacturer, AVC, about the smaller capacity boiler need. They are aware of the need but for now are dealing with that capacity slot with modulating electric boilers in the European market. I don't know how they deal with DHW loads. A large storage would prob be necessary. WW

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Dave_4

>>Hey, even the tankless water heaters turn down to around 15 K.

The new Noritz tankless heaters I"m looking at turn down to 11K.
Rinnai units turn down to 15K and are available with battery backup.
.