Latest thoughts on combination boiler/water heater

BoilOver

I have an older boiler and traditional tanked water heater. Soon I will be looking to replace both systems and am considering combination units such as the navien ncb-240e. I would appreciate any thoughts or recommendations on these types of systems.

nicholas bonham-carter

One thing to do first would be to do a heat loss survey on your house, using the SlantFin app.

http://www.slantfin.com/professionals-page/heatloss.html

Next you should have a good idea of what your hot water requirements are, such as how many showers, dish-washing loads, clothes-washing loads, hot tub, etc
post those results here, for more advice.
You want to avoid over-sizing, or under-sizing--NBC.

njtommy

Navien combi is a good boiler as long as it's installed and set up currectly. Over sizing is very easy to do on this unit do to 18,000 btu minimum firing rate. You don't want to short cycle the boiler. Heat loss is a must. Do your design low temp for your area and then do it with a 50 degree day. That will give you your highs and lows. If you have small zones it's only going to make short cycling worse and a buffer tank would be needed.

jumper

If you have the room,why consider combination?

Rich_49

Perform the heat loss calc for the house as mentioned . Figure out how much hot water you really do use . Stay away from CHEAP combis that use immense amounts of energy to keep up with your hot water demand , combis that utilize a three way diverting valve to switch between DHW and space heating demands . Readily accessible parts for repair are not necessarily a good thing , there is a reason they are readily accessible , think about it .

After doing the heat loss and DHW survey decide what you really want to do . If you just have to have a combi look at these units and seriously consider them before and above anything else .

http://www.htproducts.com/versahydro.html

http://www.htproducts.com/versaflame.html

http://www.htproducts.com/EFT_Combination_Floor.html

Hard to oversize the first 2 since they utilize mass and can be fine tuned by programming . EFTC does not use a three way diverting valve but instead has a DHW circ and a space heating circ along with a generous buffer so it does not need to exert alot of energy to keep up and gets away from the cold water slugs others have .

BoilOver

jumper


Currently the boiler and tanked water heater are in our laundry room and we'd love to reclaim some space to use as a pantry. That being said, we would hate to buy a combination unit and have it fail prematurely. (Trying to get at least 15 years out of the next purchase)


Using degree day and actual gas usage our need is about 85k btu. (Assuming the old Weil McLain is as efficient as the plate says-- which I really doubt given how short the cycle times are when it is maintaining temp)

kcopp

How many showers?
If you have modest hot water usage I have had good luck w/ this unit....Meaning a Full 1 bath home
Dual coil design. 1 heat, 1 hot water.
Simple design, Very few moving parts means less to go wrong.

http://ibcboiler.com/ibc-products/dc-series/

Same Heat exchanger as this...

http://www.triangletube.com/TriangleTubeProduct.aspx?CatID=1&PID=31

nicholas bonham-carter

Of the 85k BTU, how much is heat, and how much hot water?--NBC

BoilOver

Based on a month where the water heater was the primary gas user, I estimate that about 95% of that is for heat

BoilOver

Thanks for the comments, still researching. I have 85k design day heat loss split over four zones. Does anyone have experience with the htp eftc and short cycling? It has a small internal tank, not sure if that is enough to prevent significant short cycling. Are there any zone control thermostats/systems that "work together" to prevent short cycling?