Should there be a buffer tank on this type of job?

bob eck

Home owner is building an new house. Wants to install an Navien 240 combi boiler. The home owner wants one zone radiant and the rest of the house copper baseboard.
In the kitchen they want radiant as one zone by itself. Then three other rooms on the first floor as another zone.
Second floor master bedroom one zone by itself. Then two bedrooms and master bathroom and other full bathroom as another zone.
Only kitchen getting radiant with the other three zones copper baseboard.
Heating contractor wants me to price regular copper baseboard and I will but I will also be quoting him on the heating Edge HE3 copper baseboard so they can use as low of water temp to heat the house and try to get the boiler to actually condense most of the heating season.
With these small zones should this type of job have an 30 or 50 gallon buffet tank? I would say yes.
If installing an buffer tank would it make sense to have a coil in the buffer tank so during the heating season and that tank is up to temp run their domestic cold water through that coil picking up some heat and then running it into the Navien combi boiler where that will make all the domestic hot water?
If this was my house I would be installing the buffer tank no questions asked adding a coil to the buffer tank would be up for discussion.

NY_Rob

Seems like a good solution, especially since the MBR is it's own zone and will probably cycle a lot especially if it got a vaulted or high ceiling.

DZoro

Buffer tank yes, small zones. I would size the emitters for 140* or less. Coil pick up, probably not worth the time and expense.

Zman

MY guess is that the homeowner wants the Navien because the homeowner is cheap.
It is also worth noting that the domestic side is going to do nothing but short cycle. That's just the nature of instantaneous hot water.
If you are stuck with the Navien, your buffer tank is a good idea on the heating side. My guess is that you will get not traction on the buffer tank or any other efficiency suggestions. They just want their inexpensive combi boiler.

Ironman

Yes on the buffer tank, no on the Navien combi, and no on pre-heating the domestic to the combi. It won't like that.

Ironman

Why not a good mod/con + an indirect + a 30 buffer? If you're dealing with a tightwad, you can use an electric water heater for a buffer tank, but the HTP 30 gal buffer tank is very reasonably priced.

Zman

If you use a properly sized mod/con and an indirect, you might not need the buffer.
The Navien turns down to 18k and will short cycle on the DHW side no matter what.
Many of the new mod/cons will turn down to 8k, problem solved?
I think this just comes down to the owner. If they are cheapskates and just want an inexpensive combi, let them have it. 5 years from now when the short cycling wears out the boiler, they can do it right.
If they are receptive to it, give them the mod/con + indirect option.
I like to start that conversation with "how long are you planning to live here?".

bob eck

Vaughn has very inexpensive buffer tanks from 10 gallon to 119 gallon models.

Solid_Fuel_Man

I've done the 40 gallon electric water heater buffer with great results. The elements are 1" pipe thread. Big box sells cheap 40 gallon for peanuts. And you can feel.good about getting the cheap one as it will be in a closed loops system and will not rot out!

EzzyT

Depending on the required water temp required for the heat edmitters one can go with HTP UFT (which would be my choice) and use a Turbomax reverse indirect tank as both buffer and indirect tank which would be piped in a two pipe buffer tank configuration. I would definitely stay away from a wall hung combi unit. If there stead fast on going with a combi unit then go with the HTP Versa-Hydro just as long as the supply water temp required for the heat edmitters isn’t above 160 and not over a heat loss of 100,000 btus.
That’s my two cent.

hot_rod

Anyone try the Argosy buffer shown on the ad to the left?

My one question is why the connections are so far up and far down the from tank ends. Seems like you would not get full use of the tank?

When you look at piping options, the 3 pipe connection method seems to best leverage the tank and provide the lowest possible return to the boiler, heat pump, whatever. That drives the best efficiency of the heat source.

Although 3 port tanks, not so common, need a 4 port and plug one connection.

bob eck

Vaughn 30 buffer tank not much more than an 40 gallon electric water heater from the DIY stores.
Buffer tank very easy to pipe.
Vaughn buffer tank pricing is very competitive vs Boiler Buddy or Lochinvar.
I have not priced the Flexcon buffer tank that is advertised on this website.
Vaughn has a Featherweight indirect water heater that is plastic and I think they should come out with an plastic buffer tank if it will cost less than this stonelined buffer tank.
The weight difference alone will help the contractors back out.

Solid_Fuel_Man

I dont think I'd go for a plastic tank of any kind. No oxygen barrier, exposure to boiler water temperatures etc. Cheap metal electric water heater is less expensive, and 10 gallons more.

Plus: you get a couple of new heating elements, and thermostats from it for service on another job.

hot_rod

Solid_Fuel_Man said:

I dont think I'd go for a plastic tank of any kind. No oxygen barrier, exposure to boiler water temperatures etc. Cheap metal electric water heater is less expensive, and 10 gallons more.



Plus: you get a couple of new heating elements, and thermostats from it for service on another job.

Or leave the element in for a dual fuel source. I switched the 120V element to a 5500W fof 18,755 BTU/ hr backup heat source.

Gordy

Interesting input about oxygen diffusion in a plastic buffer tank. Especially where that will see higher storage temps.......

Solid_Fuel_Man

I'm leery of anything plastic or non metal in a heating system. We all know about piping materials, so of course hePEX etc has a proven track record.

I dont even like some boilers which have a plastic manifold system on those old Gionanni HX.

Even Victaulic piping with the rubber has proven to not work out so well in a closed loop heating system.

hot_rod

I think composites are okay in hydronics. Some of the combi boilers have composite pump volutes now. With the HX, air vent and shuttle valve all built into the one piece block.

Gordy

Those are small parts, and portions of the whole system. Throw in a sizable buffer tank there is a lot of surface area for O2 to infiltrate. Bright side if done correctly most of the O2 can be eliminated in same vessel. Which could be the engineering thought process.

Brewbeer

Ironman said:

Why not a good mod/con + an indirect + a 30 buffer? If you're dealing with a tightwad, you can use an electric water heater for a buffer tank, but the HTP 30 gal buffer tank is very reasonably priced.

Agree.

Brewbeer

The heating edge baseboard is quite pricey, more than 2x the cost per foot than the higher output versions of the more standard baseboard manufacturer offerings.

I looked at the heating edge baseboard when I designed my system (see link in sig), but the higher output did not make up the higher cost vs. using longer runs of more traditional baseboard (not including labor costs for installation) .

NY_Rob

I made this comparison chart when planning my HE2 emitter upgrade. In some rooms there was just no way to add additional std fin-tube to make up for the btu output loss going from 170F AWT to 130F AWT so I had to go with the $$$ HE2 baseboard.

Brewbeer

The Slant Fin 30 is pretty underwhelming in output. I used Sterling's Heat Trim Plus line, the output is 20% less than the HE2 per foot, but costs 60% less per foot (again, not including installation costs).

NY_Rob

^ nice, HE works well... but is is big $$.

Problem is nowadays that nobody wants to see radiator- push something is front of it!

bob eck

Vaughn buffer tank is lower cost than the HTP Boiler buddy.

Brewbeer

I'm not sure where to put this, but here is what I think is some interesting data I've been collecting from the Loch WHN055 modcon with buffer tank installed in my house in 2015.

NY_Rob

^ great numbers.... wish I could go so low!

Say it's 40F outdoors- you have 99F SWT... do you get any heat out of your baseboard fintube with 89F AWT?

Brewbeer

At a 99F system (top output of buffer tank) temp, the dT of the baseboard supply and return is about 2-3F (99 out of buffer to baseboards, 96-97 back to buffer). At that temp the boiler is about 102 out and 98 return. The boiler pump (15-58 on speed 1, 60 watts) moves much, much more water than the system pump (Viridian 2218 on speed 1, 8 watts).

Even when the system is running at it's highest capacity with temps down around zero, the baseboards run a delta of less than 10 degrees.

When it is in the 40 and 50s outside, the baseboard runs a delta of less than 1 degree.

NY_Rob

^ big advantage to having a buffer tank!

That's where fin-tube baseboard sucks... get low temp SWT and the DT is down to nothing real quick. That's one area where cast iron baseboard shines... it take a long time to get up to temp... but it stays there for a long time too so it prevents boiler cycling like a buffer tank does.

Solid_Fuel_Man

Yes, cast iron (all types) drives huge deltas with near room temp return water. With 1CPH thermostat settings, bu the time its warmed up and the return temps rise the zone is satisfied.

Gordy

Brewbeer said:

At a 99F system (top output of buffer tank) temp, the dT of the baseboard supply and return is about 2-3F (99 out of buffer to baseboards, 96-97 back to buffer). At that temp the boiler is about 102 out and 98 return. The boiler pump (15-58 on speed 1, 60 watts) moves much, much more water than the system pump (Viridian 2218 on speed 1, 8 watts).

Even when the system is running at it's highest capacity with temps down around zero, the baseboards run a delta of less than 10 degrees.

When it is in the 40 and 50s outside, the baseboard runs a delta of less than 1 degree.

You should try the nimbus controller with the 0-10v variable speed pumping in the boiler loop.

Remember system side should be greater than boiler side flow. think about the efficiency gain.

Brewbeer

RE: cast iron baseboards, If I had been thinking about it when I designed the emitter array, I would have installed cast iron baseboards on two of the levels in the house where I had the access. There would have been enough cast iron water volume to equal the volume of water in the buffer tank, and the radiators would be the buffer. The money spent on the buffer, could have gone to cast iron radiators. But I'm probably glad I didn't go that route, since I installed the radiators myself, and I'm not as young as I once was.

Gordy said:

You should try the nimbus controller with the 0-10v variable speed pumping in the boiler loop.

Remember system side should be greater than boiler side flow. think about the efficiency gain.

I do think about it. Granted it's down in the "barely measurable" range, but one of the goals of my system design and install was "how efficient can it be". I'm guessing the boiler side loop is flowing ~8-10 gpm, and the system side loop is flowing ~2-3 gpm.

My WHN has a 0-10v output for controlling boiler pump speed, but I don't believe the variable speed boiler pump was available when it was put in. Are small, variable speed pumps now available for my unit?

NY_Rob

Brewbeer said:

RE: cast iron baseboards, If I had been thinking about it when I designed the emitter array, I would have installed cast iron baseboards on two of the levels in the house where I had the access. There would have been enough cast iron water volume to equal the volume of water in the buffer tank, and the radiators would be the buffer. The money spent on the buffer, could have gone to cast iron radiators. But I'm probably glad I didn't go that route, since I installed the radiators myself, and I'm not as young as I once was.

I installed a 10' and 9' section of the Gov-Board/Baseray in the addition area of our house two summers ago. It was lots of fun getting them into position and connected to each other by myself. In the end, it was well worth the extra effort because that 19' of cast iron not only completely solved the small zone short/frequent cycling problem but because of the high mass slow to heat/slow to cool (and the radiant heat) properties of the cast iron rads it made that room into the most comfortable area in the house.

We have some land in cold, cold upstate NY, we hope to eventually build on it and retire there. I am already set on using cast iron baseboard throughout for excellent comfort and to get top efficiency from a mod-con boiler.

bob eck

When sizing the copper baseboard for this type of job what temp BTU should I use?
I do not want to use 180 degrees at design temp should I use 160 degrees so the coldest hours of the heating season max temp to get proper heat would be 160 degrees.
Would this help the boiler to condense sending water temp out at 150 - 140 degrees or lower so return temp would be under 130 degrees to make the boiler condense.
If this was my house I would make sure there is plenty of copper baseboard to only go up to 140 degrees on the coldest days of the year so most of the heating season outgoing temp would be 120 and lower making the boiler condense as much as possible.

NY_Rob

If you can size radiators for 130F SWT (120F AWT) on DD you'd be in pretty good shape the rest of the year. Once the CH water has been circulating for a while the DT will be 10deg or less on fin-tube. I would imagine that on a new, tight home with decent insulation and good windows/doors a SWT of 130F on DD won't be a problem especially using HE2.

What was the heatloss figure on DD?

Solid_Fuel_Man

I would look at another type of emitter if I were designing new. Copper fin tube BB ends up being the entire perimeter of the house, and by that time there is still only a few gallons in the entire system.

bob eck

Person who is building this house wants copper baseboard with a Navien combi boiler. They have a friend who is a plumber and he told them that is what they should use. When using copper baseboard and having four zones that is why I am recommending and 30 or 50 gallon buffer tank to give the system some water volume. It’s not my house and I would not do it this way but the Plumbing and Heating contractor told me this is what the home owner wants.
Since the home is going to have an boiler I asked if the home owner would consider putting radiant in the garage and basement before the concrete floors are poured. He told me no way does the home owner want radiant in the garage and basement. I told him just get the pex tubing installed in the concrete the home owner can hook the radiant zones up to the combi boiler at an later date. Man you just can’t talk to some people.

Solid_Fuel_Man

My father in law is like that! Minimal baseboard "because hot water is better that hot air" and a Viessmann set to the highest setting....

A lot of people associate hot water heat with copper fin tube only. It's like there is no other emitter.....

Brewbeer

I designed my system around a 130 F SWT at the design day (0 F).

NY_Rob

^ is your design based on HE2 or conventional fin-tube?

Curious as to the heatloss/sqFt of a new build modern home?

My 1960's 2x4 construction home comes in between 15-20 BTU/SqFt.

bob eck

If it was my new construction house I would put in best insulation, windows and doors to keep heat loss down.
Design system with condensing gas boiler and use 30 or 50 gallon buffer tank with HE 2 copper baseboard in some zones and other zones would be radiant. Max water temp going out when at design temp would be 130F trying to get biggest delta T with low return water temp. With today’s building materials and insulation you can tighten up a house for low BTU loads.
You could even use cast iron radiators (they would be no where as big as the ones in older homes built in the late 1800’s and early 1900’s) or aluminum wall panel radiators. Like you said it does not need to be copper baseboard.

hot_rod

panel rads are a nice in between choice between fin tube and cast iron BB. still quick responding but a bit more water volume, easy to add TRVs..