Need advice. New SIPS construction, Hydronic slab on grade, Mod Con combi or Stand boiler / On DHW

DAVIDSEIDEL

New construction SIPS, very tight, 6 1/2" walls, 12" roof. 4 bdm, 3 bath
Calculated Peak load is 35,800 Btu/hr required, 60,000 Btu specified.
Been looking at IBC DC 20-125 or Lochinvar Noble NKC 199 for heating and DHW.
Reading here lately, I am wondering if I should just go with 85% efficient boiler and on demand DHW.
Wondering if the ROI is there?

Also, to add to the mix is a 40 X 40 X 12 SIPS shop that has 3/4" lines running to it for the shop in floor heat.
Initially, I was going to have a separate boiler, but was told to heat it from the house boiler (more efficent).
This heating load was not included in the house heat load calc.

Thanks,
David

hot_rod

I think you will find that conventional non-con boilers really are not that much cheaper to purchase.

Considering all the features and higher potential efficiency, go with a mod con, and indirect. Or a Combi and a small buffer tank.

The largest unknown is future repair costs for the more parts intensive mod cons.

Brewbeer

What is heat loss of shop. How far is shop from house boiler.

DAVIDSEIDEL

Thank You Hot Rod.
Brewbeer,
Nearest I can figure with online load calc is 30K Btu. It is 6 1/2" SIPS walls, 40 X 40 X12. Conventional trusses, 17" blown in insulation. 3 windows 32" X 42", 1 service door, 10 x10 insulated door. 3 /4" linset is 120' from manifold in shop to future boiler on house. Custom 2" thick styrofoam enclosure between buildings. More styro over top of that, 2 feet deep.

DAVIDSEIDEL

Forgot, 2 zones in shop. One 16 X 25 to be heated at 65 and the rest will be at 45-50, unless I want to work in that area, I will bump it up. There is a NG Rinnai 38k btu in the bigger part to boost up until hydronic slab gets warmer.

Solid_Fuel_Man

I too would go with a mod/con and for a Cadillac system go with an indirect, or heat pump water heater. A Combi, especially for your low heat load will really short-cycle. Slab on grade is made for a mod/con, the lowest operating temperature of any heat emitter.

A typical 80% boiler would have to worry about return protection, and as @hot rod said, are not any cheaper than a mod/con, especially when you figure a chimney into the equation.

JUGHNE

Also, very tight house will need combustion brought in for conventional boiler.
Usually awkward to achieve on standard equipment.
Plus chimney vent somewhere.

But 199??

GroundUp

I'll leave the boiler banter to the others, but my concern is your lines to the shop. You say custom styrofoam enclosure- what does that entail, exactly? Will this enclosure effectively block out 100% of groundwater infiltration or is it 4 pieces of EPS formed into a box around the tubing? This is a very important piece of the equation

Gordy

It would be ironic to go to such great extents with your envelope to then go with a mid efficiency boiler.

I didn’t happen to see what emitter type the house will have? I know shop is infloor.

If house is in floor also, those are the kinds of emitters with low return water temps that really squeeze the high efficiency out of a mod/con.

I’m partial to making hot water with an indirect using a mod/con. You can size for the heat load, keep the indirect warmer, and make that hot water with a high efficiency appliance.

Combis are great in the right scenario. But way oversized for your heating load, and still limits gpm depending on size, and incoming temps.

Gordy

As far as a ROI who knows what forward fuel prices will be. We have enjoyed pretty low costs over the last few years. At least if the tide turns you would be ready for it. Also make that ROI a little shorter time table. What fuel will you be using? LP, NG?

DAVIDSEIDEL

Thanks for all the input guys. I am glad I found this site.
GroundUp, yes the styro is 6" X 8" all glued together and sealed the best I could as I put it in the ground with spray foam at the end joints 15' - 20' pieces of 6" X 8". I made a trough and layed the tubes in there, then glued the top down as I buried it. Cannot say it is totally water tight. Soil is sand, good drainage.

Gordy, house is slab on grad with in floor heat.
Natural Gas fuel.
I am putting in a small wood stove/glass door for ambiance/doomsday. So I can heat no matter what.

I really appreciate the help/responses.
David

Gordy

With a mod/con if you get the return water down in the 80’s which is easily doable with your envelope the efficiency is mid 90’s. Much better than a mid efficiency boiler which may only be in the low 70% range.

DAVIDSEIDEL

OK, so new plan is Mod/Con with indirect DHW, sized for load on house and shop. Both in floor hydronic, well insulated.
Now I need to educate myself on zones.
Should the house just be one big zone? The 2 car attached garage a zone at 50 degrees. Will it introduce too many variables if I have 3 zones in the house?
The 40 X 40 shop will have 2 zones.
David

DZoro

I like 2 zones in most homes 1 for the bedrooms, other for the rest of the house. 3 zones are fine but you start to get into smaller btu's than the boiler can do without short cycling, or adding a buffer tank.
Lochinvar Noble now comes either in a combi, or boiler only, very impressive boiler and company support. But your installer is key, if they don't do flue analysis, combustion testing, find someone else.

Rich_49

Room by room heat loss will tell you how many zones . To be on the same zone rooms should have similar BTUh sf requirement , similar finish floor R value and similar use pattern . That is of course if you're shooting for comfort first then efficiency .

I seriously question the load of this house also . How big and where is it ? If you already stated , sorry , I missed it . A 4000sf home we designed in Ann Arbor Mi was only 31,000 BTUh at -7* design . That home is ICF which has a much lower R value than your described SIPs home , or kit should . You really need to look at ACH by way of having a blower door performed .

The Steam Whisperer

With extremely low heat loss and if you have a decent amount of solar gain, using a MOD CON probably makes no sense. Well insulated structures not only have a lower heat loss, but due to internal gains from people , cooking and solar, the heating season is much shorter. Your building balance point is probably about 50F ( the average daily temp when heat starts to be needed), which is equal to moving a house from Chicago to San Francisco in terms of heating cost. Does it make sense to install a mod con in a home in San Francisco? To put it another way, if you cut the heat loss in half, your fuel usage doesn't just drop in half, it drops more like 70%. Add in the increased electrical usage of full outdoor reset "high efficiency" hot water boilers due to additional pumps, blowers and electronics and pumps running nearly the whole heating season, instead of only a third to a half, and the savings drop even more. Factor in much increased maintenance costs, higher repair costs and probably only 1/2 to 1/3 the life of an old fashioned cast iron boiler and I wouldn't be surprised if upgrading to a "high efficiency" hot water boiler has a negative payback. And almost anyone can get a old fashioned hot water boiler running when it goes down with standard, non-proprietary parts. Of course, a radiant floor system already has inherently high electrical usage compared to other type of hot water systems due to the increased volume of water flow necessary ( 10F temp drop for design, instead of 40F for good panel systems, or 4 times the electrical usage) and the high pressure drop of the system. The other "problem" that may occur is that the floors will not feel warm because the heat load per square foot is so low that the floors don't need to provide much heat, so they run until slightly above room temperature.

I used to install nice firetube mod cons, completing all the combustion checks, flow design calc. etc , but don't any longer. They really don't make much sense in most apps, especially in very efficient buildings where the fuel savings may be 20% of very little cost in the first place.

Gordy

So @The Steam Whisperer (Formerly Boilerpro) you would install a ci boiler that at their smallest would be twice the size needed for this particular heat loss? Add a buffer tank for additional costs? Boiler return protection?

I understand completely what you are saying about the simplicity, maintenance, life span (which varies greatly with water quality).

As far as emitter types panel rads would be maybe a better option since warm floors are a thing of the past with high r value tight structures. Neutral would better describe the floor temp which in my book should be the goal any way. Warm floors are a unintended consequence of high load structures.

We still don’t know location, and orientation of the structure. Maybe the poster would share more details.

DAVIDSEIDEL

Location is 35 miles north of Mpls/St. Paul, MN.
Orientation is South Facing, Lots of shade in summer.

Solid_Fuel_Man

I built and live in a "super insulated" 3200 square foot home. R32 walls, and R55 ceiling, less than .3 ACH infiltration. I'm at 14 btu/hr/square foot @-40F.

I use a partial reset on a mod/con, where the curve is not perfectly heat matching. A standard digital thermostat set to 1 cycle per hour. Building only calls for heat at night on all but the coldest of weeks. Leaves you with a warm floor in the morning and solar keeps it warm in the afternoon. Slab on grade with refinished cast iron radiators on second floor, which rarely call for heat. CI rads are run at the same temps as radiant slab. 110F is the highest temp I ever use. And standard wet rotor circulators not even ECM. Only two circulators total in system.

My total electric consumption in the winter is less than 250kwh, that's for a house with a well and stay at home wife with kids etc.

I dont agree with the above statements about high electrical costs etc.

The Steam Whisperer

Gordy: I would say there is really no need for a buffer tank when the system itself is high mass ( I'm assuming it's a slab). I work on a slab system with a building load of about 100,000 btu/hr and it is feed off a 1, 600,000 btu/hr steam boiler with a heat exchanger. When that zone is running by itself it can absorb the full output of the boiler for nearly 20 minutes or more before the boiler finally shuts off on pressure. Water temperature going out is still only slightly warmer than tepid A properly sized single input will run very, very long on cycles and very, very long off cycles... the best operation for highest efficiency. It's just like old converted gravity radiator systems.... the mass of the system creates it own reset of system temperature. Return temp protection is easy to provide with a simple P/S bypass loop at the boiler, just don't run the pump continuously. At low boiler temps, almost no heat is transferred to the system. As the boiler warms up, then heat transfer to the system begins to increase. When the boiler shuts down from a heating cycle, even if it was running fairly cool, the boiler heat soaks and the casting boiler temperature rises considerably, drying out the casting if necessary. Using the cheap light weight, low water content Weil Mclain CG boiler is probably one of the better choices for this app. If there is a domestic water load, then the bigger boiler will still be necessary.

Solid fuel man:
Running multiple pumps and draft inducers is always going to cost more than just running a single pump and possibly a draft inducer. The electrical costs for running a radiant floor system may be much lower than forced air, but still will be much higher than a simple radiator or panel system. Running the system without full reset will cut the pump run time down considerably from the near 100% on time of a full reset system. What you are doing with your system sounds very similar to how the system would work with a simple cast iron boiler. The slab is charged with heat in a large burst and then coasts with no pumps running for long periods of time. This can cut the electrical consumption dramatically. You are probably running your system at near minimum electrical usage. However, my previous 3200 sq ft 1903 home with high mass standing radiation and just a little bit of rad floor and a peak load of about 50,000 btu/hr required about 12 watts peak total pumping capacity using a non ecm pump. If I had balanced the system well, I could probably cut that power usage in half and then half again with an ECM motor ( but they don't come that small) The boiler transformer and controls need only about another 20 watts. 32 watts of peak electrical usage to heat a 3200 sq ft home in northern IL I'd say is about as low as it can get.... and without using anything complex.

Gordy

@The Steam Whisperer (Formerly Boilerpro) Ahh ha! finally someone who gets it. Not to hijack the thread, but My previous house with ceiling radiant, and floors from the 50’s had a wm cgm boiler with 210k input. Heat loss was 65k. Boiler bypass was the only protection. One circ for whole system which was all one zone.

I called it indoor reset as the supply temp was dictated by how long the heat call was, which was dictated by the outdoor temp.
The longer the call the warmer the swt got until satisfied. Highest swt ever was 115*.
That boiler didn’t ever see above 95 rwt, but as you explained on shut down it was well above dew point which dried the HX out between calls. That boiler is a 1993 install still going strong.

GroundUp

@DAVIDSEIDEL I am concerned about this insulated box you've created. What is the total length of line buried between the structures? I have replaced miles of failed attempts at insulated underground, many no different than what you have described. Sand or not- when (not if) the water gets in the enclosure, you are effectively pouring 20-50% of your heat into the ground depending on distance. We carry a waterproof, frostproof, darn near bulletproof underground line that is all closed cell foam within a thick outer casing that is designed for this purpose and cannot be beat in these type of installations

What stage of construction are these buildings in currently? Talking about zoning, it sounds like the floors may not even be poured yet? I cast another vote for mod/con with no buffer and an indirect WH by the information seen thus far. If this is something you want someone to put eyes on, I am not far from you. Maybe 45 minutes to an hour. I could drop by and take a peek if you wish, and perhaps shed some light on the subject

DZoro

Interesting conversations.
The Lochinvar Noble Boiler only can run as low as 8,000 btu and up to 80,000. With the water temps you will be needing you will easily be at the 92-95% efficiency range. Good odr, efficient pumps, slab/air sensing stats. You will be in good shape.
I have to agree with @GroundUp , I too have dug up many, many "homemade" boxes, including my own in the 80's. They just are not worth it, many prefab options available out there. It's amazing how much water they will absorb up after a few years.

Gordy

Solid_Fuel_Man

I would install a ThermoPEX product in a suitable PVC sleeve. Maybe 2-4" of blue board above, beside, and below the PVC. Then you can have an expensive, yet long term solution. I too have experience with bad underground, some very costly to do which still took on water and poured copious amounts of heat into the ground.

spray foam, even closed cell will take on water when underground over time.

GroundUp

Solid_Fuel_Man said:

I would install a ThermoPEX product in a suitable PVC sleeve. Maybe 2-4" of blue board above, beside, and below the PVC. Then you can have an expensive, yet long term solution. I too have experience with bad underground, some very costly to do which still took on water and poured copious amounts of heat into the ground.



spray foam, even closed cell will take on water when underground over time.

Why oh why would you need to put Thermopex in a PVC sleeve? I bury miles of it every year and have beaten the crap out of it with heavy equipment trying to extract a failure to no avail unless you catch it with an excavator ripper tooth. In which case, the PVC would also be compromised

Solid_Fuel_Man

Just the electrician in me I guess. To keep it totally dry, at least in theory. Ability to pull it out,( straight run only). I'd make very long radius bends with my PVC oven.

I like sleeving things, and we all know that a carefully installed PVC underground will have a fighting chance at staying dry.

Most electrical conduits are not properly glued (solvent welded) as a real pipefitter would and fill with water.

The Steam Whisperer

Gordy:

It took me several years to figure the whole thing out with how the bypass piping and heat soaking the boiler worked. Learned the need to shut off the pump at the end of the cycle rather recently. I ran the pump continuously one winter and basically rotted all the lower nibs off my boiler. All the 4 way mixing valves, injection pumping and all is generally not necessary in most systems. We all love the shiny things, but really most aren't needed and probably not the best solution. Just let the physics do the work and leave the complicated stuff for someone else's headache. Walls of zone valves or zone pumps with all the piping can be replaced with simple trvs. and a single loop of piping. Cheaper, just as effective, and maybe more so and a whole lot easier to maintain and service.

DAVIDSEIDEL

Great feedback! I will try and address the questions in detail tomorrow. Got to sleep.
The house is up, approximately 2500 square ft total. Currently, I am almost finished wiring it. Now I am a little concerned about my piping to the shop.
Might have to abandon that and go back to the original plan of shop having it's own boiler. GroundUp, I will contact you. Thanks!

hot_rod

Whisperer you said

When the boiler shuts down from a heating cycle, even if it was running fairly cool, the boiler heat soaks and the casting boiler temperature rises considerably, drying out the casting if necessary.

If the boiler was running cool say 100 return, 130 supply, where does the boiler heats come from to dry the castings and flue?

I guess without knowing exact numbers that would be hard to predict or assure?

DAVIDSEIDEL

Current picture.

hot_rod

Great looking home, I like the red metal.

All things considered an accurately sized mod con would be my suggestion. And the lower you can run the SWT, the more efficient it will run.
While a conventional cast or copper boiler may be less $$ and simpler to maintain and repair, it would require combustion air into the mechanical room, a B vent thru the roof, and would not have all the nice control options, ODR, ramp delay, modulation, data and diagnostics, etc.

The Steam Whisperer

Hot rod:
The heat in part comes from the castings themselves. The water temp maybe only 130F, but the casting temperature, on average through the thickness of the casting, is much hotter. The fireside surface of the casting is much closer to combustion temperature. Its just like an internal combustion engine, when you shut it off, the cooling system temp rises. In addition, for most boiler bypass piping schemes, the delta tee through the boiler is more like 100F return, 180F supply at the end of the boilers cycle, so once the pump shuts off, the temperature in the boiler equalizes from return to supply and rises due to heat soak. Just try it sometime and you'll see. Another common examples of this effect is when a boiler is running at very high temps and then the flame and pump shut down at the same time. The water temp rises so much that some of the water can flash into steam. The copper tube and water tube mod con boiler manufacturer's are especially in tune with this problem and often have delay on break relay for pump shut down so this excess heat can be carried away and not cause pounding in the boiler. We see it on lower water content cast iron boilers too. The Weil CG's are especially low water content, only about 1 1/2 gallons for typical residential sizes, so it is pretty common to have pounding in these boilers when run in zoned baseboard systems. However, this makes them good candidates for low temps systems using boiler bypass.
Also, the 140F minimum return temp widely believed for cast iron boilers only applies to boiler's running at very low excess air levels... around 20% IIRC. Typical modern atmospheric boilers run about 50% excess air, so the condensing temp drops down much lower. You have to be more careful with the older cast iron boilers with cast iron burners, they usually run about 20 to 30% excess air. Sort of backwards.... the older boilers ran at higher combustion efficiencies than newer models.
Of course, if you don't trust a standard boiler bypass, you could just install a Thermix valve at the boiler and pipe it P/S. I used to do this all the time, but found that bypass piping works just fine and it eliminates the second pump if you want.

BTW, the Hydrotherm KN series and Ray cast iron condensing boilers rely in part on this principal of heat soak to dry out the castings at the end of each cycle.

The Steam Whisperer

Oh, here's a pic of my temporary cobbled up set up on my own home boiler showing the piping/ pumping configuration that I use. It ain't pretty, but it's getting the job done until we get the new naturally induced vacuum steam system in place so we can put in much smaller radiation and piping. The boiler ( which I had pulled out of another home during a replacement) is a pretty rare model. It's a regular Dunkirk PVWB model, but it was the year or two of production that used the new more efficient heat exchanger and the older more efficient cast iron burners. It runs about 20% excess air and shows about 84% to 85% efficiency on the combustion test... a good 2 to 3 points better than the current models. The new equipment is going into a fireproofed room which will be supplied outdoor air. Providing outdoor air is not a big problem if you keep your fired equipment isolated from the living space. I believe this is good practice for fire and CO safety whether the boiler is atmospheric or a mod con.

According to the Gas Company our fuel usage is in the lowest 5% of comparable homes in our area. We do have pretty decent insulation now ( r-15 walls and r-22 attic in Chicago) but have been doing extensive remodeling through the winters ( exposed exterior walls and ceilings and storm windows only sometimes in some rooms). I figure once we get things tightened up and get the heating equipment in its own room with dedicated combustion air, we'll probably drop down into the lowest 3% in usage with a heat load of about 35,000 btu/hr. When you're only paying about $600.00 per year for gas, saving another $75.00 per year by installing a mod con doesn't work out economically. Even if gas prices double or triple ( which is probably more in keeping with long term pricing), it still doesn't make sense financially when adding in the shorter life and higher maintenance and repair costs.

DAVIDSEIDEL

House is 2554 sq ft on first floor, additional 816 2nd floor, and there is an additional bonus rm with 486 sq ft above the garage that would require about 25 degree delta from garage below at 50 degrees. So..... 3370 sq ft and I am heating 612 sq ft of attached garage space to 50 degrees. I will attach a picture of my doomed homemade insulating apparatus. It is 2" owens corning polystyrene.

hot_rod

Got it, same effect as when vent dampers close and block temperature rises. With the pump shutting off with the burner, how high does boiler temperature rise? Maybe a 60 second post purge would be a compromise, use that block heat, but not pulling the block to room temperature?

A thermostatic return protection 3 way valve is much like the super simple, reliable, low tech TRVs, but with a 3rd port.

I encourage their use when dealing with high mass, systems, conventional boilers as a cheap insurance policy. As most owners and some installers are not as aware as you about extended condensing conditions in conventional boilers.

DAVIDSEIDEL

Pex insulating channel/ box

DAVIDSEIDEL

Sips panels are R26 for 6 1/2" walls and R51 for 12 1/4" roof at 25 degrees. R values go down to R23 and R45 at 75 degrees.
Shop is appox. 75 feet from house but the total run is around 115 -120 feet to get from Utility rm in house to near center of shop where pex comes up.

hot_rod

When I installed OWF I ended up with InsulSeal pipe for the lines. 4" PVC with whatever foam R-value you wanted, glued, sealed and taped joints. Blast hole liner on the outside to protect the foam insulation. They will build most any size pipe and insulation. Two 45's to come up out of the trench.

This allowed S&R plus room for a 1/2 pex water line, low voltage wiring for sensors. Lines could be removed and replaced.

1" PVC in the trench also for wiring pulls.

That pre-insulated pipe doesn't really have much insulation, if any between the S&R, so it's a heat exchanger also

You did a great job with the insulation, but ground water may get in and rob a bunch of your BTUs?

The Steam Whisperer

Hot Rod:

The average boiler temperature doesn't rise, it just equalizes. The 180F water at the top of the boiler transfers heat to the lower temperature water at the bottom of the boiler, driving its temperature up. Hotter castings transfer heat to the lower temp water. There probably even some heat transfer from the combustion chamber and burners that moves up into the boiler castings and then the water.

Just try it out sometime and you'll see.

hot_rod

I'll buy some transfer from the hotter castings, flame temperature around 1800F, wall temperature typically in the 300F range. So with thick walled cast iron, I see some additional transfer after flame is out.

But when flow stops in a vessel hot generally rises, colder fluid drops, stratification principle. The taller the vessel the more thermocline. The principle behind gravity powered hydronics, the greater the ∆ the faster the stratification.

I'm not questioning what you are seeing, just cautioning that all systems may not behave like yours and return protection is still a simple addition when high mass is involved.