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Best setup for Radiant and Snowmelt. Viessmann Vitodens 200?

CDecker Member Posts: 17
First I just wanted to say how much I enjoy this forum. There is a ton of information archived here, and I’ve learned so much from you guys over the years. I’ve even spoken with some of you via PM and phone calls, and everyone has been extremely helpful. That being said, this is my first post, and I am looking for some design advice.

I have a 2500 square foot home in Buffalo, NY currently heated and cooled via forced air (Trane XV95, 100,000 BTU) with no problems. Furnace was spec’d and installed before renovations, when house was 1,800 sq ft and had NO insulation.

In 2010 I built a 24x32 detached garage. I installed 2” of ridgid foam board under the entire slab and perimeter, and installed (3) 240’ loops of ½” pex on 6/12” centers. I ran the pex back underground through a 6” PVC pipe into the basement of the house, pressurized it with air, and left it. The garage is well insulated with closed cell spray foam. I installed (2) natural gas Reznor unit heaters (45,000 BTU on the 1st floor, 30,000 on the 2nd) and they currently have no problem keeping the Garage at 58-60F all winter, at minimal cost.

In 2011, we replaced our basement floor to add drain tile, replace plumbing, etc. During this time I also installed insul-tarp (I know, not great, but I couldn’t afford the head room loss with foam board) and (3) 240’ loops of ½” pex on 12” centers in the new basement slab. The loops were brought out in the same corner of the basement where the garage loops enter.

In 2015 we built a 700 Sq. Ft addition, sided the entire house adding 2” Rigid Foam board to the exterior, and closed cell spray foam in all exterior walls / roof / basement walls. The house is now extremely tight. During this renovation I also installed (6) loops of staple up radiant under the 2nd floor bathrooms, master bedroom & 1st floor kitchen for floor warming. I did not use plates.

Last fall I purchased (2) 6 loop manifolds, and separated them by temperature. I put the (3) basement slab loops and (3) garage slab loops on one manifold, and the (6) staple-up loops on another. I may add a 3rd 6-loop manifold down the road, for staple up under the remainder of the 1st floor.

I downloaded RadiantWorks, and performed a detailed room-by-room heat loss calc on the house and garage. I put in every wall, window, R-Value, etc. I spec’d the staple up loops as floor warming, and the garage and basement slabs as heating. On a design day, the software is telling me the BTU requirement is 68,000, however that is not taking into account that both the garage and house are already heated with forced air, so I’m thinking the real world number is much less?

While searching for boilers and creative ways to control the radiant, without it fighting with the forced air, I learned about the Vitodens 200 and constant circulation. I talked to Paul Pollets, as well as my local Viessmann rep via phone, and I’m pretty sold that the Vito 200 is the way to go for the radiant. I think I could go with the smallest 200, the B2HB-19, which modulates between 12,000 and 68,000. I would use outdoor reset, and put it on constant circ. with no interior thermostats. I would make the Staple-Up my high temp circuit (HC1). I would use a Viessmann mixing Valve Kit on the manifold with the slabs, and make them my low temp circuit (HC2), with it’s own curve. I would ditch my current 12 year old Bosch Tankless, and run an indirect setup off the primary loop on priority. It might take some dialing in the first winter with the HC1 Curve to get a good balance between the forced air and the radiant, but after that I think it would be a smooth setup.

So it seems like I have it all figured out right? So your probably wondering why am I posting here then? Well, this is where I need some design help from the pros. After seeing a couple local systems in action, and reading and talking to some of you on this forum (Snowmelt, CPUJohn, Etc.) about your setups, I’m sold on the idea of snowmelt. We are pouring a new driveway this year, and I want to add snowmelt to it.

The driveway is approx. 1500 sq ft. I have designed a layout using (12) 200’ loops of 5/8” pex on 6” / 9” centers. I would use 2” ridgid foam under the entire driveway, as well as along the edges, just like I did in the garage. RadiantWorks is telling me that my BTU requirement is approx. 200,000 BTU’s (Approx 130 BTU’s/Sq Ft). That’s with 50% Glycol, R-10 below, Buffalo, NY location, etc…

Since I haven’t purchased a heat source yet, I can approach this from several angles, and this is where I need some help. Some have suggested just going with a bigger Vito 200, large enough to do both, but I cant say I’m a huge fan of that approach, and I feel it will leave the boiler’s lowest modulating point to high for my radiant demands when its not melting snow (most of the time). I had someone else suggest a second Vito 200 for the Snowmelt, but that seems like an extremely expensive, smart, and complicated piece of equipment, just to melt snow for 4-5 months and nothing else. I’ve read threads here where several people are using inexpensive 200k BTU Takagi, Navien, or even Rinnai tankless units, and have had great success. The Vito 100 looks appealing, but the BTU requirements don’t go high enough to meet my demands.

Does anyone have any suggestions? Do I keep the systems separate (what I’m thinking), or try to bring them together? Would an inexpensive tankless work for the snowmelt, or should I be looking for something fancier?

Now if it would be possible to “combine” a second (larger) Vito 200 with the B2HB-19 being used for the radiant, that might be cost effective (Common venting & Exhaust, 1 Low Loss Header & Sensor, 1 Primary Pump, Etc..) I would want it to still be able to modulate down to 12,000 though when no call for snow melt exists, and call for help from the second unit when melting snow or for fast DHW Production. Is that even possible? Would it be worth it?

Thanks again for you time!



  • HVACguyinME
    HVACguyinME Member Posts: 25
    Yes, I’d have a professional redo your driveway. That sounds a little too low. The driveways I’ve done which have been in that size-ish have been 300k - 450k. Yes I do live in Maine where we design to -6, and yours should be 6. But again, it sounds low. The boiler I have been using is the IBC SL series. It’s control is great for snow melt and radiant designs. Some people get scared setting them up, but the control is great for systems like this. Plus the control can be hooked to internet through Cat 5 cable and do so many different things with it.
  • Zman
    Zman Member Posts: 7,334
    For your home and garage design, it sounds like you have the math handled. Do be careful of your temps on the concrete side. Concrete slabs will take a ton of energy on a cold start. If you get the constant circ working well, it will not be an issue. If you find yourself trying to heat a cold slab it will drag down the boiler and leave the higher temp zones wanting.

    On the snowmelt, I would suggest twinning the primary boiler and having it serve the snowmelt. The 200,000 number should work fine with adequate insulation.

    As for the boilers, when twinning, it is better to use the same size. What about finding a couple of 110k-125k models with better turndowns. Nothing against Viessman but they are quite expensive and work very hard to make things excessively complicated.

    In any event, the trick to managing cold start slabs, interior or exterior is to limit the output to the slab through delta t. The system will have a fixed gpm. If you fix the delta t, the slab can only take a set amount of energy and will warm up nice a slow.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gordy
    Gordy Member Posts: 9,514
    If it were me I would keep the garage, and snowmelt systems separate from the house. In saying that will the garage be maintained always during heating season? 200k for snowmelt, and the garage has supplemental heating. The snowmelt takes priority over garage when needed.

    You didn't say what the house load alone is. So you could get a smaller mod/con possibly for just the house. Not viessmann, but there are some 50k 7:1 out there a Lochinvar KHN. Low end of 7.8 k.
  • CDecker
    CDecker Member Posts: 17
    Thanks for the replies and suggestions guys. To answer some of your questions:

    HVACguyinME - I designed the snowmelt to 0 with a wind speed of 10. I designed the house to -10 with a wind speed of 10. I did not design the snowmelt as low as the house, because if it gets that cold (-10) then first, it shouldn’t be snowing, and second, I would probably shut the system down as it most likely wouldn’t keep up anyways.

    Radiantworks asked me what class of snowmelt I wanted (Snow Free Area Ratio) and gave the following results, based on my selection. Snowmelt Shielding remained at Suburban, Capable Load Percentage – 95%, and Maximum Snowfall / Day – 24” remained constant.

    0.0 – (Class I) – 64.07 BTU/h ft2
    0.5 – (Class II) – 90.78 BTU/h ft2
    1.0 - (Class III) – 128.24 BTU/h ft2

    These numbers do seem low, especially the 64. I wouldn’t even attempt that. Perhaps this software is not what I should be using?

    Zman – Great points that I hadn’t really considered. I’m curious what the Viessmann guys here think. I would think that with a Low Loss Header sensor, and with temp sensors in the mixing valve, the boiler would be able to compensate for cold slabs? Like you said though, once the system is up with constant circ, it will probably be a non-issue. Also keep in mind that both the house and garage are currently heated with forced air. The house is at 70, the garage at 58. Using an infrared point and shoot thermometer, the garage slab is at 56 right now (on the surface), and it’s 0 out. That being said, I don’t think the slabs will ever be “cold” to the point that I think your referring to? I do like the idea of twinning, and I’m not stuck with Viessmann, it’s just what has come most suggested to me for this application.

    Gordy – Thanks for the reply, I’ve been reading your posts for years, and I appreciate your input. At this point, it might be difficult to separate the basement and garage slabs, as I have them going to the same 6-loop manifold, and the pex is all spray-foamed in the wall. I could pull the manifold with the basement and garage loops over to the snowmelt side, keeping all the “slabs” together (and glycol’d), but now I’m probably looking at a significantly larger snowmelt boiler? Perhaps I could give priority to the basement/garage over the snowmelt? I was not going to run glycol through the basement or garage slabs, due to the fact that they are both heated via forced air all season. I do realize that could be dangerous, especially for the garage, so maybe putting it over with the snowmelt would be a great way to protect it (with glycol), without adding a flat plate and everything else involved with that to the radiant (house) boiler. To answer your other questions, Yes, the Garage is maintained always during the heating season. There is a woodworking shop out there and I need to prevent condensing tools. According to Radiantworks, the loads are as follows, but keep in mind they don't factor in the forced air:

    Garage – 12,524 BTU/h - Heating
    Basement – 10,255 BTU/h - Heating
    House (Staple –Up) – 21,757 BTU/h - Floor Warming

    Total Flow: 6.8 GPM
    System Head: 3.9’
    Boiler Load: 68,162
    System Volume: 43 Gallons
    Total Heated Area: 3078 ft2

    I do like Lochinvar products, I’ll take a look at the model you mentioned. A neighbor has a heated driveway using a KBN-400. His driveway is approx. 3,300 sq ft, so 400,000/3300 = 121 BTU/h FT2. His system works flawlessly, even during some of our notorious lake effect snow bands. Seeing that my driveway is half the size of his, I’m thinking 200,000 for the snowmelt should be ok?

  • Gordy
    Gordy Member Posts: 9,514
    Looking at your break downs I would still go seperate only the snowmelt though. Where is the 68k? I come up with less than 45k for the staple up, garage, and basement.

    Many ways to skin the cat. I always look at cost.

  • Paul Pollets
    Paul Pollets Member Posts: 3,509
    I'd read Dan Foley's excellent article on designing and installing snowmelt systems:

    Better to have a dedicated boiler for the snowmelt that's sized correctly and a separate boiler for the home.
  • CDecker
    CDecker Member Posts: 17
    @Gordy Looking back at the RadiantWorks reports, they are spec'ing "Radiant Capacity", "Required Heat", "Back and Edge Loss" and coming up with a "Total Radiant Panel Load". The sum of all of the "Radiant Panel Loads" is 68,000, I was providing the "Required Heat" numbers. Perhaps there is better software out there I should be using...

    @Paul Pollets Great article! I've read it before, and just read it again. I will without question be insulating the entire slab, both underneath and around with 2" foam. I am planning 12 loops at 200' using 5/8" pex. I agree that putting the snowmelt on its own boiler and system is probably the best way to go. Choosing the power plant is another issue. Your a Viessmann guy, am I right in thinking the 100 is ideal, but to small for this application, and a properly sized 200 (with all of its bells and whistles) is overkill for this application? What am I left with? (2) 100's? A different manufacturer? Recommendations?

    I've read and spoke to people on this forum doing this exact setup with 200,000 BTU Tagaki Tankless Units for 1/4 the cost of a properly sized 200. I realize a mod con boiler is the right way, but how do I justify that?
  • Gordy
    Gordy Member Posts: 9,514
    So you do cheap, and possibly do it again down the road. Might get lucky. Your wallet in the end plays the hand. I would not sacrifice the home heating to the snowmelt.
  • hot_rod
    hot_rod Member Posts: 16,344
    Nothing wrong with a copper tube boiler for snowmelt if you are looking to save $$. Not sure how often it will operate to realize the $$ difference between 87% copper tube boiler and 90-92% mod con.

    To keep a dedicated snow melt boiler exercised some installers put the indirect on that boiler also, plenty of HP to quickly recover DHW, even with snowmelt operating, prioritize DHW.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 1,567
    I think Gordy is right. Separate the SIM from the house. What I have done in the past is use a flat plate heat exchanger between the boiler and the SIM system. The Sim system has an Radiant Extrol 30, a Honeywell supervent, a Taco I-Series set point mixing valve, a Caleffi Y strainer, a grundfos pump, a Webstone bibb, and a tridicator. I guess you can use a sensor with a Taco I-Series with an outdoor reset. This is so I can have anti-freeze in the SIM system and not in the house system. I fill the Extrol 30 with 10 psi on the bladder and pump the system to 15psi. I get all the air out when I pump the system.

    I use the setup to add fluid to the SIM system that "HotRod" made up with an Extrol 30 tank and a Caleffi fill valve and connect it to the system's Webstone bibb and leave it for a week or two to fill the system after I purge the air out. I pressurize the bladder to 30-39 psi and pump it up to 65 psi so a lot of fluid is in the tank. This Extrol 30 is a different one than the one on the SIM system. It's worked for me.
  • HomerJSmith
    HomerJSmith Member Posts: 1,567
    Fill "HotRod's" tank with an anti-freeze solution if you are connecting to a anti-freeze system. Fill it with conditioned water if connecting to a conditioned water system.
  • CDecker
    CDecker Member Posts: 17
    @hot rod Putting the indirect on the Snowmelt Boiler w/ Priority is a great idea. One of my concerns going with the smallest Vito 200 (12k-68k) for the house, was that it may be a little lacking BTU wise for the indirect. This would solve that problem. Would the glycol be an issue for the indirect tank?

    I could also leave the domestic on a tankless (how it is now), but I was planning on going back to an indirect when we bought a boiler.

    You also read my mind regarding the snowmelt. I don't mind spending more on the house system, and I don't mind saving more on the snowmelt system. Even though I am in Buffalo, it still really only snows 4 months out of the year. Some of those snowfalls can be intense, but I'm not expecting 1,000,000 BTU performance. If it keeps the slabs relatively snow and ice free without salt, chiseling & scraping, I'm happy, even if it takes a little longer to do it. Now if it doesn't work at all, that's just a waste of time, resources, and money. That's what I'm trying to avoid.

    @HomerJSmith Great ideas! Do you have any pictures of this setup? If I used a completely separate boiler for the snowmelt, the glycol wouldn't be an issue. Is there a benefit to using outdoor reset on a Snowmelt system? I would think as long as I'm above freezing, I'm melting. Maybe I'm misunderstanding your setup...
  • Gordy
    Gordy Member Posts: 9,514
    What are your dhw needs as far as recovery? A 40 gal indirect will out perform a 40 gal gas tank style which has about a 36 k burner. Store at 140-150 mix down and have extended usage on the 40 indirect.
  • HomerJSmith
    HomerJSmith Member Posts: 1,567
    No pictures. If you plan for a manual system where you expect a storm and you can turn on you SIM system, you can get the driveway up to sno melt conditions before the storm hit. But, if it is an automatic system you are going to need a sensor in the driveway or separately mounted sensor and the SIM system will turn on when the temperature is close to freezing and there is moisture present. There will be a lag time for the driveway between when it comes on and when the heat emitter is brought up to temperature. The driveway is the heat emitter.

    You have to decide which class of system you want. Class I is effective about 90% of the time as there will be times during a storm when it is overwhelmed. I was always told to sell a SIM system as a 'sno removal augmentation system'. There will be times it just doesn't happen and you fall back to the time honored sno removal system--a shovel.

    With the lake effect, Buffalo is a challenging situation.

    As to outdoor reset, it's debatable. Sno usually falls between 15 deg and 35 deg. You just don't want to shock a concrete slab with too high a temperature and ODR would boost the temperature, the colder it got. You want just the temperature to melt the sno and not so much that you heat half of Buffalo.

    I assume the PEX is in the driveway and spaced so you don't get banding and the tube length for each circuit is not too long and there is insulation under it all so you don't get back loss.

    If you are old, SIM sure beats a shovel and heart attack.
  • Gordy
    Gordy Member Posts: 9,514
    Personally I would prefer manual. Saves operating costs. Anything is better than manual snow removal. However some would prefer an app for that........ It depends on occupancy life style.
  • hot_rod
    hot_rod Member Posts: 16,344
    The higher class systems are intended to keep up with an ongoing snowfall and are often idled. A hospital helipad for example.
    I think you can get weather responsive controls now that monitor weather stations and could fire up based on a storm prediction. If you trust the weather people :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • wyradiantguy
    wyradiantguy Member Posts: 5
    We install radiant and snowmelt in Wyoming. We always keep the two systems separate as most of the time you don't need glycol in the house system. We run about 40% mixture in our snowmelt here and it does very well, costs a bit less to pump and replace as well. There is a picture of one of our snowmelt systems in operation during the winter on our website. www.iwantradiant.com
  • CDecker
    CDecker Member Posts: 17
    @HomerJSmith Thanks for the response. The PEX is not in the driveway yet, but I have it drawn out. Pour will be this summer if all goes well. Looking at 5/8" tubing, 12-loops, 200' long. Most of the driveway will be 6" on-center, with some less-important areas at 9". 2" rigid foam under and around everything. Approx 1,600 sq ft area.

    @Gordy @hot rod I'm also leaning towards manual control, and I have no intention of idling the slab. I would be curious the cost difference between idling it and letting it cool between each snowfall though, but that will be and experiment for when its in.

    I will most likely install the Tekmar 091 Socket and conduit when we pour, just in case I decide to add automatic controls later. When it comes to Buffalo weather, I never trust the weather people. :) Wi-fi switches are so easy to come by these days, and it wouldn't be hard to rig something up if I wanted remote access via smartphone.

    @wyradiantguy Thanks for the response. I visited your site, nice work! I've pretty much decided on separating the systems at this point, but the question still remains regarding heat source(s). What manufacturer do you prefer?

    I talked to another local plumber here yesterday that recommended (2) Viessmann 100's (one for the house, one for the snowmelt). He thought a 200 for my house was overkill, considering the small load. This was just a quick recommendation based on my description. Unfortunatley I don't believe a B1HA has the balls to melt a 1,600 sq ft slab, so unless I reduce the amount of driveway I'm melting, or start doubling up 100's ($$$) for the snowmelt, I believe that options out.

    Perhaps I should've labeled this thread "What is the best heat source for radiant" and "What is a good heat source for snowmelt". Do I need a $3,000 boiler to melt snow when a $800 tankless will do? I guess thats really what I'm trying to figure out...