Question for my own home combi boiler

Sorry not sure if this should be in general discussion or not, if it is I can repost it. Looking for a little help with my boiler. I have an original 1965 Burnham holiday Natural gas boiler, still runs but costs a fortune to run. Plan on installing a high efficiency combi Navien unit for my baseboard and hot water. Any suggestions on the combi units, good, bad ? Thanks for any help with this


Thanks Larry, I’ve read the majority of stuff I’ve been searching on Google. I was wondering if anyone had any personal experience or installed these things.

I can’t help you there, Drew…sorry.

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Its definitely time to switch out that old inefficient boiler.

Be aware of output from a combi unit. They’re great but don’t have the ability to support a large load for jetted tubs.

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Thanks Scott, no jetted tubs here, 1.5 bath house pretty standard amount of water use. Thanks for the heads up wasn’t aware of that

No worries, just throwing it out there to see what kind of feedback I get

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Make sure that you have the capacity to deliver enough gas to the unit to meet its max input BTU rating.

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I’ll have to double check. I believe my boiler has a 3/4" running to it but my gas service was updated 2 years ago and the majority of the piping is 1" and not a very long run maybe 25 feet from meter if that. They may need to update some of the pipe where it enters to my utility room now. Good thinking on that

Got it.

A combi unit might work great for you. Is the water heater portion of the boiler separate or completely integral?

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Yes making sure you have adequate gas line is important.
If you’re replacing one boiler with another of like BTU output and it is a combi unit, they typically don’t require resizing of the gas line like a new install of an on demand/tankless style water heater.

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Completely integral, I also just checked the navien model that I believe would work on my home and its max 150k btu that says it can be run on up to 24feet of 1/2" gas pipe

Lp or Nat gas?

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Drew, Scott Frakes is a great resource. He has many years of HVAC experience and is a straight shooter. He live about 2 hours from me, too. :smile:


Sorry Scott didnt see the replies. Natural Gas , I just got a quote yesterday on a navien NCB-210E but it’s a little more than I hoped for so waiting on my next quote on Monday. The quote for monday will be on a Bosch

No worries my friend.

180,000 BTU is a large boiler. Do you need that size?

Not trying to doubt anyone but have your installer do a heat loss if he hasn’t already.

Bosch makes a good boiler.


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I honestly thought I need the 150k btu model the I’m only 1500 sq ft. The estimator said nope you should go with the 210 because it has a higher flow rate of 4gpm compared to 3.4 gpm for hot water. He has to do a manual J since it’s a loan through my utility provider. Not really sure but the price was $10,850 which seems way to high for a single zone and in his own words a straight forward easy set up. So I’m going to see what the installer who uses Bosch equipment says. I originally thought this should be about 8k to install, maybe I’m wrong

The larger boiler will modulate down but the cost is indeed higher.

Yes, a Manual J is necessary and the best way to go for sizing.

One thing that may be driving the cost up is primary/secondary piping and pumps.

Other good brand names are Lochinvar Knight boiler and Weil-McLain Aqua Balance. Just some other names that have been out there for awhile.

Best of luck!

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I hope you took into consideration that your boiler is 55 years old… these new units will never last that long. Although advertised as less complex, they are not. They require heavier maintenance and easily lose their efficiency if not kept in topnotch condition. The efficiency advertised is what you get from a brand new unit in a lab, not in real world. If you have to replace 2s in 15-20 years, how much in energy savings do you need to recoup the cost of these fancy gadgets. They should be installed for convenience, not energy savings.

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Thanks simon. Yep I like my current boiler theres nothing mechanical to it which is probably why it has lasted as long as it has. The high heating costs are its biggest downside , Unfortunately I know that it will be a matter of time before I do need to replace it. My water heater has been having issues and will need replacement soon though. The new unit will also allow me to finally clear up all my floor space and finish the room how I want to and I will be able to remove my rusty b vent from my roof when I get that redone in a few months. (not really a big factor but it’s a plus) my wife and I do plan on moving in under the next 10 years or so, I’m also hoping that this may add a little value to my home. At the very least allow me to sell my home easier than having a 65 year old boiler when it goes on the market. I’ve been weighing out the pros and cons.