Boiler replacement and tankless heater vs. combi boiler

davecsomething

So we got estimates from a local guy that comes highly reviewed in the area.

We want to a) replace the boiler (most important, since it's getting pretty old, and we've had some pressure issues lately) and b) switch to a tankless water heater (also important, but less pressing at this time).

He gave us estimates on

1) A Combination boiler/water heater
2) Just the boiler upgrade (research says it s a good, efficient unit)
3) Just a tankless upgrade.

The estimate on the combination boiler came out to around $ MORE than getting both replaced separately.

Other than space (which isn't really an issue for our basement), what benefits are there to getting a combination boiler over getting both units separately upgraded? Again, we can replace BOTH separately for cheaper than switching to a combi apparently.

HVACNUT

No option of a boiler with an indirect water heater?

What's being used for domestic hot water now?

Did the local guy do a heat loss calculation?

Jamie Hall

In a more direct answer to your question (though @HVACNUT 's questions need to be addressed!): there is no advantage other than space and, possibly, having only one device to worry about. It's rather rare that a combi can be correctly sized for both the domestic hot water demand and the structure heating load -- either you don't have enough hot water, or you have a boiler which is too big for the heating load.

Properly sized separate units or an indirect, if you have the space, will give better service -- at least in my opinion.

nibs

We installed a combi a couple of years ago, and think separate units would be better, we have a space problem, so felt a combi was the way to go.
This simply a personal judgement, but listening to the combi shift gears from DHW to boiler, and back, we hear valves operating, the pump going on and off, the burner going on and off etc, I think separate units would not have to work as hard.
So far the combi has worked flawlessly so have no complaints in that regard.

ArseniyM

Combis, in general, are a lousy fit for most homes. They're meant for a large home (lots of heat loss) and moderate DHW usage. Since you haven't really posted anything about he house, no one here can tell you much about which way to go.

hot_rod

I am a big fan of combis, you can get them down to a 110K with turn down they can be sized much smaller than typical non modulating boilers. A 110 should give you 3 gpm or more of DHW, which is adequate for most residential applications.

On feature that is key is being able to lock the turndown for the heating side, or ramp delay features. I have mine locked at 30% output for heating.

I've heard combis now make up about 40% of mod con boiler sales?

JUGHNE

What were the "pressure issues"?
If the boiler building pressure and opening the relief valve is the problem, then it is most likely the expansion tank getting water logged......something that can happen with any hot water system.

PS, also how much money have you have to pay for maint of the old system? Over how many years?
IMO, you will put more maint cost than that in any new combi, tankless or ModCon unit over the same number of years.

EBEBRATT-Ed

@davecsomething

You will get many opinions and we are always debating these issues on this forum. not a question of right or wrong.

Just my opinion.

and I am assuming you using gas for fuel if you taking about a combi.

Tankless heater and combi boiler are ok they are more expensive to purchase and install, somewhat more efficient and require more service and maintenance in most cases.

A standard boiler is less expensive, usually less service and parts are less $$ than a combi

Longevity is another debated issue

It's not one size fits all. What's best for you may not be the best choice for the guy down the street

Jamie Hall

I might add to @EBEBRATT-Ed 's comment -- the mark of a true heating professional (and @EBEBRATT-Ed us one, for sure) is that he or she will sell, install, and repair what is the best solution he or she has available for the customer's specific situation. Unfortunately, there are many who will sell a specific solution, or brand, or whatever, without analyzing the customer's situation.

Timco

Many or most combi units and wall hung boilers are imported and rebranded. Look for major name brand parts inside and not all generic knock off parts like pumps and gas valves and blowers. Proper sizing is everything. Routine maintenance like de-scaling is a must for proper operation. Be sure it’s installed to be serviced easily.

MikeL_2

A combi or modcon boiler may be worth the extra initial cost if your heat emitters are sized so the units will operate in their most efficient condensing mode.

motoguy128

Combi’s present challenges in that many have limited output, flow restrictions requiring a high delta T. I think they are good for high mass radiant floor heat where space and cost are a concern.

That being said, much much better off with an indirect and boiler if Space isn’t a concern. Nearly the same real work effeciency with a mod-con is setup right when you factor in short cycles. NO issues with low flow or short bursts from a faucet of washing machine fill cycle.

A small 40 gallon indirect can outperform a 50 or 60 gallon conventional or 75-100 gallon(s) electric setup. You can get continuous Flow for a single shower head with a 100k or larger boiler.

Alan (California Radiant) Forbes

"...he or she will sell, install, and repair what is the best solution he or she has available for the customer's specific situation."
A rarity these days, especially in the middle of winter.

Only one mention of a "conventional", atmospheric water heater? Inefficient as hell and here, you have to replace it every 15 years. But my smart customers soon realize (because I tell them) that if there's a rare power outage or if something goes wrong with their boiler, they still have DHW; a distinct advantage, no?

However, if you have a 500 gallon Japanese soaking tub, an on-demand solves that problem. Customers like my indirects because I tell them it will be the last water heater they buy and if they have a postage stamp-size mechanical area, a combi may be their only option.

Consider that DHW costs $25/month for the average family. Don't stress over the perfect solution or even most efficient. Consider projected cost of repairs and downtime as well.