what size boiler and indirect h2o heater?

kk

We're getting confused and need an unbiased opinion. We're installing radiant heat throughout 2800 sq ft house. It's sandwich method. btwn subfloor and hardwood with alum. transfer plates 8" on center. The net heat load is 77k. There are two water temps. 1/2" hepex tubing. wirsbo alum ht transfr plates. Some concrete, some hardwood, some carpet. 1/3,1/3,1/3 apprx. We will use an indirect hot water system as well. The master shower has 3 bodysprays, a handheld and a shower head. The tub is big. We are trying to decide what is enough/ big enough to heat the floors and the domestic hot water without going overboard and wasting. The options given to us are: buderus g-234x64 boiler, pro-mix controller, 2 plus 100 water tanks, plus pumps and mix valves etc. Or the buderus that is a size smaller, OR munchkin w/ 935 control with the 2 pluss 100 tanks, pumps, injection tank, etc. Our guy thinks we need 250+ btu boiler and 150+gallon water storage. We don't know what this really is in practical terms except for the unbelievably high cost. Do we really need all this water storage? Is 60 minute dhw regeneration too slow? is 25 minute regen too slow? Is 35 minute?? We like to take long hot showers but we won't necessarily have everything running at once. This just seems kind of excessive. The smaller buderus system is $5100 . The next size system is 7100.and the munchkin system is 9100. This is for boiler and dhw storage and contrls alone. I know that much of this is personal preference but we just don't know what this really means. I don't want to oversize. Thanks for your time.

Alan(CaliforniaRadiant)Forbes

If you

don't want to oversize, then forget about the 250K BTU boiler; it will be short-cycling like crazy when it's heating your house; size the boiler to your house load (77K) and put in a 100 gal. indirect water heater on priority which will dedicate your boiler to making hot water when the water heater calls for heat.

The Munckin 80M or 140M with a Vision I reset control would be ideally suited to your house.

A 1 hr. recovery rate for domestic hot water (DHW) is fine; you don't need anymore.

Another option is to go with a separate "flash" type water heater like a Takagi or Rinnai; they will provide you with unlimited hot water depending on your flow rate.

Best wishes,

Alan

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hot_rod

With a lopsided load

sounds like your dhw load far exceeds the heat load. A modulating boiler, a seperate boiler or maybe a seperate condensing water heater may be other options.

Run some numbers and get a better idea on the actual dhw load. Find the shower flow rate and tub capacity. Most important the owners dhw exceptations

hot rod

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bruce pirger

In my new house, I have a tub/shower with two independent controls and shower head spouts...trying to encourage the wife you see. I have a MegaStor MS-53 (53 gallon) indirect and a Buderus G115-21 (60,000 BTU/hr). If I run both shower heads for about 15 minutes, I run out of hot water. If I run one, I can run forever. They are rated at some 2.5 gallons per minute, so assume 4 gallons/min with the two of them on together...The timing is just about exactly right when you consider 53/4 is just under 15 mins, and the little boiler is cranking away.

I totally agree you're better off with a smaller boiler that just runs more to heat the hot water. How much hot water you need...that depends on how you want to use it. If you run your many headed shower at full blast for 20 minutes, just figure how much water you need...and I'd say if its something you really want to do often, just get that much storage. Same for the tub.

I'm NOT at all a professional...but this is how my thoughts worked in designing my house. And I'm happy...albeit a little disappointed that I run out of hot water with two showers going together...but that's a rare occurence. Sadly. LOL

kevin coppinger_4

boiler and h2o htr.

don't oversize just for the domestic hot water. Prioritize and add a sparco or the like type mixing valve to get you through high demands. (might work for you Bruce)How big is the tub? , you say big...# of gallons?
What is the fuel choice here (NAT gas or LP). either the Buderus or the Munchkin are great choices.
kpc

jerry_2

any opinions on the GFX waste water heat exchangers

I was reading this thread and got an idea. I would think a reasonably sized tank could cover most bath tubs, so it's the shower that's the tank killer.

I have not put one in, but have been looking at the gfx technologies waste water heat recovery setup. You plumb the cold water up a setup that has a copper pipe wrapped around a copper sleve that replaces a vertical segment of the waste stack. They claim over 50% of the waste water heat is captured. With a thermostatic shower control, I would think this would double the available shower time. The units run a few hundred dollars plus plumbing, which sound a bunch better than a monster water tank.Can you route either the shower cold water or the hot water heater source to run past the waste stack?

Now I have no experience with it, but it makes sooo much sense I had to bring it up.

jerry

kevin coppinger_4

i have one...

ready to be plumbed up in my house and I have one in the field. It runs with a Vaughn 50 gal Top Performer and Sparco mixing valve... Family of 7 and they have plenty of hot water. kpc

John@Reliable_2

Hot water, and lots of it! Oil fired hot water heater

kk, if oil is available you might consider an Oil Fired Hot Water Heater. I have never seen one run out. Running joke around my area , put one of these in and have enough hot water for the neighbors too!John@Reliable

hot_rod

waste water hx

probably my biggest concern would be fouling. The waste that goes down even a shower drain usually has lots of soap or shampoo. I suspect this will coat the coils and reduce efficiency. Same with hard water. I know it scales copper tube HX's from the get go! I think I would plumb them in with a couplw flush ball valves to run a descale agent through them.

Still a clever idea to recapture some "drained away btus"


hot rod

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Joe_13

Bruce

The specs on a MS-53 call for 146K gross BTU boiler for quicker recovery rates. Probably why you're running out of hot water under heavier load.

Mike T., Swampeast MO

Recently got my master bath running--sounds similar. 2 regular shower heads, 5 body sprays, 2 handhelds (all rated 2.5 gpm except in "champagne" mode which is higher); large corner Jacuzzi tub.

110 gallon natural gas tank-type heater rated 75,000 btu; 68 gal/hr recovery, 1" tank connections, 1" hot water main in gravity recirculation loop (½" return on loop).

3/4" Grohe thermostat valve in shower; 3/4" Grohe tub filler.

Tub fills (90 gallons or so) in about 9 minutes. Plenty of hot water to fill tub (immediately after SHORT shower) with heater set at lowest "hot mark" on dial (about 115°). The in-line electric heater in the tub seems a VERY good idea as the water temp (particularly when air is added to the whirlpool) can drop quite rapidly and would require added hot water for a long soak.

While shower valve can handle everything operating at once it's somewhat overwhelming and (in my mind) wasteful. In full-blown tryout with two people in shower--long shower using sprays/handhelds/scrubbers it did not run out of hot water with thermostat set such that it was nearly total hot water (some like it HOT--not me). May sound crazy but with the way I like to shower it might actually save water--get wet/hot, turn down/off flow, soap up, turn down temp and blast away for a few seconds with the body sprays. The initial cold blast from the sprays is especially invigorating.

I would imagine that if you can set up your DHW system with similar ratings that you'll be fine in most foreseeable uses. While I don't have one, many SWEAR by a large dummy tempering tank for DHW.

James_2

My opinion...

Try to keep it simple. Showers are dump loads which means you need to store the volume of water for the device you which to service. (ie: fill the tub = 100 gallons @ 104 degrees) ( take a shower 3 gpm @ 10 minutes = 30 gallons at 104 degrees) (take a body shower 3 heads @ 3 gpm @ 15 minute = 135 gallons @ 104 degrees. The size of the boiler will be determined by how quickly you would like the use the same amount of water again. So, if you fill the tub, how long do you want to wait to fill it again or run a shower etc... This is up to you. If you are going to use a large amount of water I would suggest high efficiency equipment with efficiencies of 92% or higher. Radiant floor heating and domestic hot water are excellant applications. Your home needs a system that will not be oversized for the heating load so modulation is a must. I would suggest you have your Munchkin contractor quote you a 140M Munchkin with the Vision-I package and (1) 119 gallon storage tank with a good quality Thermostatic mixing valve on the domestic hot water. (don't forget the thermal expansion tank) The Vision Package will provide outdoor reset which will limit the radiant water temperatures requiring longer run times and lower water temperatures and higher efficiency. The Munchkin will modulate down to 43,000 btu/hr which is about 1/2 your design load and better than any 2 stage boiler on the market you can find. The Munchkin is a low mass boiler (less than 1 gallon of water) so it will respond quickly to the demand. The Vision-1 system will prioritize the domestic hot water for quicker response times and tank recovery. The Vision package is also available with an extended parts and service warrany for 5 years. So, what would you get with the Munchkin ? Approximately 150 gallons of usable water immediately,(mixing down from 165 degrees to 104 degrees) and will deliver about 2.5 gpm continous from the boiler which would completely recover a cold tank in less than 45 minutes, and how many times is that really going to happen? If it does the Munchkin will be chugging away at 98% efficiency warming all that cold water. The Munchkin has a stainless steel heat exchanger, the Superstore tank is stainless steel and has a lifetime warranty. Hmmm, I am biased, and I am not ashamed....hope this helps...

bruce pirger

Absolutely no question about it....the 60K boiler output is not even close to the spec on the MS-53. But for our house, no huge tubs and whatnot, the 53 gallons in the tank is all we'll ever need. Unless we all take showers immediately after the other and two at a time...and even then it will be somewhat long showers.

One at a time...the 363 temp sensor reading in the megastor drops down about 10 degrees...then starts climbing back up.

I did fill up the kids pool outside (maybe 500 gallons or so) with "warm" water the other day.

I don't have one of those MegaMansions...nor the ummm, how do I say, "attitude" that usually goes with it.

Personally, save for the fact I had to reset my BF3 once (and only once), I couldn't be happier. Nice to know the boiler can run for an HOUR on just 0.5 gallons of fuel! YAHOO!