Replace hydrotherm with Gas boiler or High efficiency boiler

jack604

I have a hydrotherm hc-135 boiler providing hot water to my radiant heating ( 7 zones, 2 zones in basement connected to poly b inslab, 5 zones connected to based board fin tubes). The boiler is working but my heating bills seem to be increasing during the winters. House insurance would like me to replace the boiler. Does it make financial sense to goto  a 95%+ efficiency boiler (navien, viessmen) or goto a gas-boiler 82% (raypak h135).

Hot_water_fan

How many therms do you use per year?

jack604

Just added my bills, past year was about 2607 therms, this includes hydrotherm boiler, 40g hot water tank, BBQ and stove tops

Hot_water_fan

Oh wow! That's a quite a bit. A high efficiency boiler works by using lower temperatures, which allows the gas exhaust to condense, thereby transferring more energy for the same input. Baseboard isn't the best for it, so there will be a portion of the winter when the baseboard portion won't be condensing. It depends on the heat loss to linear feet ratio: you might be condensing 99% of the year or much less. There are some other benefits to modcons - they're usually well fitted to the heat loss size compared to older boilers so there's less idle loss. The newer cast iron boilers can thermally purge, but their size is working against them still.

There's no real "right" answer, both have pros and cons. However, you have a pretty favorable situation here due to your high gas usage.

Steamhead

@jack604 , first thing I'd do is get someone qualified to look at your present boiler and system. Something may be wrong with it that can be easily fixed. Where are you located?

hot_rod

7 zones certainly favors a modulating boiler
A heatload calculation would be a good start to determine the actual load.
Could be the current boilers is oversized in addition to being low or mid efficiency. Does it run on an outdoor reset control? That too would help increase efficiency, on either type of boiler.

Mad Dog_2

As long as you are prepared to Do (or have a guy to do)  the annual maintenance on the Mod Con (a few hundred bucks a pop) that they ALL require,AND purchase a spare parts kit, (Great idea), The mod con WILL cut your gas bills.  Just make sure you don't have any gas leaks on the piping.  Many buildings small ones that  waste ALOT of gas, but you're not going to smell them.  Gave it checked also.  Mad Dog 🐕 

jack604

Thanks you for all your responses.
@steamhead I'm located in Vancouver Canada. Everyone that looks at it says that's old...they don't make it anymore. You've gotten your money's worth nad not much you can do if it's working.

@hot_rod haven't done a heatload calculation, it was the one that came with the house when it was built. No outdoor reset that I'm aware of.

@Mad Dog_2 what's annual maintenance of a mod con consist of? I annually bleed my system, change the thermocouple when needed and vaccum inside the burners, anything else a new mod con would need that a 35 yr old cast doesn't need.

Also if I get a new boiler installed I'm considering replacing my dhw with either an indirect tank or go with instant dhw via a combi. Below is picture of my current set-up.

hot_rod

Those two combustion air ducts would go away with a mod on. Or combi upgrade. I suspect some heat goes out and cold air come in those vents, even when it required by the boiler or WH.

walterk55

I seem to be using 600 therms per year. Most come from heating with my old HydroTherm 125B furnace. Even if I replaced that with a new more efficient furnace that is say 20% more efficient, the resulting saving of 120 therms per year might not justify the cost of the replacement furnace