Combi choice

Bob_115 · February 8

I'm converting from oil to gas and need to decide which combi boiler to choose. The Burnham Alta and the Laars are under consideration. I was told that the Alta would need wide open taps to supply hot water as my supply line are 1/2 inch copper. The Laars has a small internal tank that would make this unnecessary. Any thoughts comments or advice would be appreciated.

hot_rod · February 8

Typically a combi starts the DHW mode based on water flow, .35 or .5 gpm flow. In some with low flow lav faucets you may need to flow the hot wide open to trigger the boiler.

Those are both good brands, Lochinvar is another.

You can run a combi "always hot" which reduces the boiler start lag. Or on demand which takes time for the boiler to rev up.

A small tank inside eliminates the lag, but maybe uses a bit more fuel to maintain the tank temperature.

Jamie Hall · February 8

Whatever — size it properly. The trick with a combi s in getting enough power for your hot water needs — 199,000 BTUh is none too much for a normal house, never mind a rain shower or somesuch — and at the same time enough turndown soo it can manage your heating load, which is usually a lot less.

Bob_115 · February 8

I've seen some comments about parts for the Laars are not readily available ,Has that been your experience?

I have 1 bathroom and i use a low flow shower head. We have learned to only use one fixture at a time.

hot_rod · February 8

for your dhw use a combi should provide plenty of water

A 120,000 would supply 2-2.5 gpm , depending on incoming water temperature. That is plenty for most showers, 1.5 gpm

If you want a bit more a 150,000 is an option.

I gad a Laars combi years ago, it was a Baxi I believe, it was 16 years old when I replaced it to sell the home

Bob_115 · February 10

I was told that to turn on the combi boiler I would have to turn the taps wide open . The pipes are all 1/2 inch copper. at what flow do these things tur on and off ? I have flow restrictors in the faucets and a low flow shower head.

hot_rod · February 10

No, you do not need to turn the taps wide open to trigger the DHW. They fire up as soon as a flow switch inside see water movement.

The spec sheet for the particular models you are considering should give you that info. Here is a Laars example. . 5 gpm seems to be a standard flow rate across the brands.

.5 or 1/2 gpm is a very low flow put a gallon container under your faucet if you want an idea of what a 1/2 gpm flow looks like

GGross · February 10

depends on the unit, I've seen some that start around 0.4GPM and up to 0.7GPM

Bob_115 · February 15

Thanks to all for responding.

Intplm. · February 15

Here is another brand you might want to consider "Rinnai" . Check um out.

EdTheHeaterMan · February 15

https://forum.heatinghelp.com/discussion/203780/combi-choice

My advice is ☑️ "None of the Above"

I am not a fan of combination heating and hot water boilers of any type. When one goes down you have two appliances that are not working. if the hot water system fails, you have no heat. If the heat system fails, you have no hot water.

Think seriously about getting a stand alone boiler that is as high of an efficiency as you can afford. If that boiler is very efficient you can take the hot water from that boiler and send it to a tank with a heat exchanger coil to heat that tank to make domestic hot water (DHW). That is my opinion on how to make hot water efficiently and effectively.

hot_rod · February 16

With a boiler and indirect, if the boiler fails, how is that different from a combi failing

No heat or DHW in either case.

EdTheHeaterMan · February 16

https://forum.heatinghelp.com/discussion/comment/1888188#Comment_1888188

Yes… but the tank still has stored heat for that last shower before the service man gets there to fix the burner. The combi-modcon is dead right away on both heat and DHW, and the tankless coil boiler has the same problem. I still believe the indirect is the way to go!

SuperTech · February 16

The best thing you can do is not buy a combi! Installing a combi is always a compromise for someone who doesn't have the space or the money to install a properly sized boiler and indirect water heater. Combi boilers are always ridiculously oversized because they need to make hot water on demand. This leads to a lot of short cycling, inefficient operation and wear and tear on the boiler. An indirect tank is a much better option. Even a stand alone electric or gas water heater is a better choice. I never recommend a combi.

hot_rod · February 16

I think all the combis now, even a 199,000 can be turned down, locked down for space heating mode

So a 199,000 turned down to 19,000 output should not be oversized for too many applications?

Fixed output boiler is oversized 80% or more or the heating season in most areas. Without modulation on zoned systems they cycle on off often taking efficiency down.

An electric wh or hpwh is an option if you are concerned about a boiler breakdown.

Or indirect with electric backup.

Intplm. · February 16

@EdTheHeaterMan I agree with your comment(s) above about combi's. But I have to remind myself that at times the combi will fit in a small place where there is little room. If the OP has enough room, by all means go with separates.

Bob_115 · February 22

I've opted to have a Burnham Alta boiler installed. Converting to gas should mean a 50% reduction in my fuel bill. Other advantages are reducing the noise of a boiler , stopping the smelly oil fumes and eliminating the occasional puff backs. I also like that the combustion air will come from outside the house.

Space is a concern also as the house is on a slab and the boiler is in the middle of the house.

the present boiler is about 80 years old and with its faltering tankless coil we are weary of military showers.

Bob_115 · February 22

I would just like to add my thanks to all for their informed advice!

Combi choice

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