CombiPLUS for Vitodens 100

gschallert

Anybody have any first hand experience with this kit? People happy with the water flow and temps? I'm a bit skeptical of it for a well water system with the colder temp and variable flow out of pressure tank. I think they advertise 3.5 gpm @ max 60 degree rise.

lchmb

I've installed a few of them. I've never heard a complaint on the HW side of things. In my house I opted for a tank. Just a preference thing...

kcopp

How many baths? How many people? I generally frown upon more than one full bath.

gschallert

2.5 baths 3 br with only two adults in residence now with occasional company 1-2x year. I don't think concurrent draw would be an issue as much as temp rise needed to get cold well water to taps in a reasonable flow rate. What happens when the well tank hits low pressure and the switch kicks the pump on. Don't combi units need steady pressure coming in like from a municipal supply? And I'm fuzzy on what happens with short frequent calls for HW without a tank. Like, coming home after hours of no HW calls and turning faucet on to wash hands before starting dinner. How does that work? Water in pipes is cool, the combi fires up but for how long? Two minutes or less and the faucet is off again. How do anything but long continuous draws make it efficient without some sort of tank. Seems like a lot more wear and tear on well pump for HW calls without the buffer of a tank. I just don't get it I guess.

njtommy

I've never work on a Viessmenn, but I've worked on some combi units and tankless units. With well you will get some pressure spikes and different temperature ranges. I have a combi boiler with a well in my own home and what I have noticed it's when the pressure drops a bit the water gets a bit hotter then drops back of when the pump kicks in. I would honestly say it's not a big temp swing I've never tested it. I would say no more then 5 degrees.

You could possibly eliminate this with a small electric hot water heater and a mixing valve. But honestly if they have the room I would just install a indirect tank.

With the combi it does take a few mins to get hot water especially in the off heating seasons when you have to heat up the water from ambient temp. Durning heating season it's not bad and is just a bit quicker.

gschallert

njtommy said:

I have a combi boiler with a well in my own home and what I have noticed it's when the pressure drops a bit the water gets a bit hotter then drops back of when the pump kicks in. I would honestly say it's not a big temp swing I've never tested it. I would say no more then 5 degrees.

Thanks for the feedback. It's my in-laws and I think the main factor for them is cost. They have the opportunity to convert to natural gas (from oil boiler & electric HW tank) but the cost of that on top of a new condensing boiler and indirect tank puts them over budget. The prices they are getting for combi boilers v. boiler + indirect are tempting. The Vitodens seems to be some sort of package deal, like cable I guess. The more you add on the better price you get on the components.

I've never had any kind of on demand HW system and neither of us know anyone who does. I said I'd ask here to try and get some real world opinions. The literature is nice but the specs are not necessarily based on practical application. Being raised on a well trains you to conserve water in general, in my experience at least, and I think they have low flow fixtures already. The specs say the combi can deliver at least 3 gpm with a cold water temp coming in at 40 F.

njtommy

3gpm @60 degree rise is a little on the lite side. Especially when dead of winter sets in with 40f well water. What would the temp rise be if the showers where 1.5-2gpms? If it goes up to 70-80f rise at lower flows you will probably be ok.

gschallert

They rate the combi boiler at 3.6 gpm @63 degree rise and just over 3 gpm @75 degree rise. The 40 F is the avg low temp of the well water in the dead of winter.

njtommy

You should be fine then.

gschallert

Thanks for the input. I'm going to keep looking for reviews online of the specific model they are being quoted. I don't think this manufacturer is very common 'cause I'm not finding much except a few short install videos on youtube. Seems to be more of a European technology and application. Would be useful if there was someplace online like here for homeowners to post their equipment and how it's worked out for them over the years.

bulldoglax

it's not a package deal like cable, the price for equipment is like anyone else.

There are many combi boilers out there and you need to go with the installer you are comfortable with. I have seen hundreds of Vitodens with combis on well and city water and and honestly I would be more concerned with water quality than pressure drops.

I am a big fan of Viessmann for the following reasons.

Limited Lifetime on heat exchanger - best in industry
5 year parts
100 years in business
US hq is pretty local to me in CT they are in RI
Easy equipment to work on and service.

So if the guy installing is good with them I would ask for references to your similar situation. If he's not I would find someone who was.

With the current situation being 2 people in the house combi is more than sufficient and if they ever sell the house the capacity would be more than enough to add a 30-45 gal indirect in the future.

gschallert

bulldoglax said:

it's not a package deal like cable, the price for equipment is like anyone else.

What I meant was I think the HVAC company was giving them a price break if they went with the component based system over sep boiler, sep water tank, chimney liner etc. I got the impression they were pushing the more modern, easier to install system and were discounting to make it competitive with the "cheaper" option of standard boiler and water tank.

bulldoglax said:

I have seen hundreds of Vitodens with combis on well and city water and and honestly I would be more concerned with water quality than pressure drops.

I'm pretty sure they have a water softening system and maybe sediment filter after the pressure tank. Is hard water the issue and would the softener take care of that?

bulldoglax said:

With the current situation being 2 people in the house combi is more than sufficient and if they ever sell the house the capacity would be more than enough to add a 30-45 gal indirect in the future.

That is definitely a factor. They are getting up there in years and could potentially sell and move south in a few years. They don't want to do anything that would neg affect resale value. The combi kit could be replaced with a tank at a later date if necessary then? Can it be re-used in a tank scenario at all or would the kit end up as wasted capital?

Thanks for the info.

bulldoglax

The newer mod con systems are not easier or harder to install than traditional systems. They are piped differently and must be done right. Again I can't stress enough to check references and make sure you are comfortable with company doing the install

In terms of water quality the flat plate heat exchangers have very small passages where heat is transferred and over time lime scale can build up and reduce efficiency. This could create pressure drops and also the reason there is an entire industry built upon descaler solutions and heat exchanger cleaning.


The combi system would add value to any two and a half bedroom house. You couldn't use it in conjunction with an indirect style tank maybe you could dump it into an electric tank but I don't think there would be any reason to do this.

gschallert

I couldn't find any friends or co-workers who have actual first hand experience with this combi boiler configuration and when they asked the company that quoted it they admitted they've installed several of the boilers but none with the combiPLUS kit. It's a tough decision when you have one option that seems better in the short term and a different option that would probably be better in the long run for resale value. The two of them living there now would probably be fine with the tankless kit but what happens to the home's market appeal if they sell and a family of 4 or 5 comes looking (it's a 3 bedroom 2.5 bath) and there's not enough DHW to support that size family/use. As a homeowner do you size capital infrastructure to the current occupancy or to the size of the house? I did what research I could for them, being an older couple in their 70's, the internet is not something they do, lol. Just glad it's not my decision. Thanks for all the feedback, I learn a great deal from the discussions here.

njtommy

Honestly I would just do an indirect tank. You would never run out of hot water.

gschallert

Just as a follow up they went with the mod-con & tankless hot water kit and are very pleased so far.

gschallert

Got to experience this setup first hand this past weekend and I was seriously impressed. That boiler is ridiculously small and quiet. We took 4 back to back showers and the hot water just kept flowing. The combi unit is more than enough hot water for the two of them. While I was there we played with some settings and I ended up turning on the combi comfort mode and lowered the outdoor reset curve being used and found the house was being kept nice and warm with the lower SWT (130 ish)

It's condensing like crazy and doesn't seem to get off low fire except for DHW calls when it goes up to two bars. I think they're going to save a ton in fuel costs this season.

njtommy

That's good news. The lower you can keep the supply and return water temps the better off that boiler will be.