boiler vs tankless HVAC

Clyde Edmonds

Currently I have a CXE 3 Crown boiler HVAC hot water system which has provided very good service over the last 17 years. I'm considering a replacement, either with  newer boiler or would like to consider some sort of instant tankless system. It is currently a single zone system and also includes a hot water storage tank. Thanks for any advice.

Ironman

No Tankless

A tankless is not designed, controlled or approved for space heating. Don't let some Internet peddler convince you otherwise - you'll regret it.



Navien, Bosch and some others make combi units that are wall hung, but they are boilers with an internal heat exchanger that heats the domestic. They work fine and that would be the way to go if you want a low end price tag.



One caution: the internal circ is only good for about 5gpm. That means you're only gonna get 50k btu's for space heating on a high temp (baseboard) system that's been designed for a 20* Delta T. Don't let the input rating of the boiler confuse you on this.

HDE_2

True

But, that would be directly connected, then many internal circulators are also limited to head factors besides flow.

If you use a external manifold or build a proper primary secondary, with an additional circulator then most those units will go over 100,000 +

No different than a Viessmann 100 boiler that is only 6 GPM heat exchanger flow but is over 100,000 DOE and IBR.

Clyde Edmonds

boiler vs tankless HVAC

Is there an operational cost benefit in going tankless? From your posts, I'm a leaning toward another boiler.

Should I be concerned with the age of my current system. I've had minimal trouble over the years but living in an extremely cold environment I can't afford breakdowns due to aging boiler issues.

SWEI

another boiler

is there a problem with the existing boiler?

CMadatMe

Temp Rise

Btu/hr delivery is also dependent on boiler delta or temp rise. GPM is just one number in the equation. A Vitodens 100 unlike other condensing boilers wants a 35 or 40 rise while all others pretty much are looking at 20 to 25 rise. The max flow rate on a WB1B10-26 is 5.5gpm on a 30 degree rise where as a WB1B10-35 max flow rate is 6.2gpm on a 35 degree rise.



Don't need pri/sec or a low loss header as long as I don't exceed these flow rates or the minimum flow rate of 1.7gpm as long as I can maintain my proper delta-t for btu/hr delivery. Boiler heads at these flow rates are 13' on the 26 and 16' on the 35. If my furthest zone is 100' that's an additional 6' of head. I would need to move 6.2 @ 22' of head on a WB1B10-35 to get the btu/hr rating out of it providing I'm maintaining my proper delta-t. It would call for a UPS26-99 on Speed 2.



I'm not predicating the none use of pri/sec or a LLH just saying it is not necessary as far as Viessmann goes.

HDE_2

chris I know

I bet you have a tough time explaining the BTUs using 35-40 DT when the unknowing are so stuck on 20 DT / 10,000 BTU per 1 GPM.



From what you write how easy is it to explain the boiler is more than a 55,000 BTU boiler to a contractor stuck on what he learned in IBR school 20 years ago?

Clyde Edmonds

boiler vs tankless HVAC

None with the boiler that I am aware. Can't seem to get rid of air in the system. I continually bleeding off air at the manifold every few days.  Just recently replaced a relay on the boiler power board.

CMadatMe

Sure Do

But the guys I deal with on a regular basis understand it. Most contractors only care about showing up on the job and when they are done the customer has heat and they collect the check. I generally don't deal with those types. Usually when I do it's to bail them out or give them a solution to a problem they cannot figure out.



The don't get it's hate when you start asking basic questions. They don't realize the solutions are based on them.

CMadatMe

Clyde

The first step is to have a room by room heat loss of the house calculated. Second step, would be to measure all the heating emitters and calculate the capable output are various water temps. Once you have those figures then you make the proper decision on the boiler that fits your application.. Suggest you contact some professionals.