Oil to Gas Conversion

sgall

I converted my home 2 years ago with some great help from this site and couldn't be happier with my system and the savings .  I am now trying to help my brother who is interested in converting his 1400 sq. ft. house located in Mass.  His current oil system is a hot water system with baseboard radiators.   I encouraged him to get a heat loss calculation and his plumber said he would get him one if he supplied all the measurements.  The calculation came back at just over 27k.  His plumber then told him that he would like to install a 120k boiler that would also run at his heat loss number.  I am no expert but this sounds crazy to me - I am assuming the plumber is suggesting a mod-con that would modulate down to his heat loss figure.  Wouldn't this basically negate the benefit of doing  a heat loss?  Aside from the massive oversizing it is my understanding that a mod-con

isn't probably the best solution for baseboard radiator system. The other issue is that it seems all of the boilers offered by the gas company are much larger than he would require.  I was wondering if you guys had a recommendation for a boiler close to his size requirement that side vents to run with baseboard?  thanks.

SWEI

19.3 BTUs per square foot

sounds about right (for a relatively well-insulated house over 15 years old.)  Assuming that number is accurate, he needs a boiler with a minimum modulation rate that is 50% or less of that number, with a higher ratio being better.  Here's something I just posted in another thread:



Most currently available mod/con boilers have a minimum firing rate of 16-17k for their smallest model.  Here are some of the lowest minimum modulation rates [in square brackets) of which I am currently aware (followed by their maximum output capacity in parenthesis):



Viessmann 200-W B2HA 19   [11,580]    (64,655)

Lochinvar WHN055                [10,450]    (53,250)

Lochinvar Cadet CDN040        [8,545]     (37,600)

Daikin Altherma                        [5,000]    (28,760)



As far as domestic hot water, keep in mind that a typical gas tank heater puts out 24,000 - 28,000 BTU/hr and the typical electric only 15,400 BTU/hr.  An indirect water heater fired by any of the above heat sources will offer faster recovery.

Aaron_in_Maine

Way too big

That boiler would be way too big for your brothers house. He wants one of the smaller mod cons out there I personally would put in a NTI TFT 60. Which is still too big but it's as close as your going to get with a mod con.

sgall

Follow Up

Thanks,  my brother is going with the Lochinvar Cadet 40,000 you suggested.   Are these smaller modcons okay to run with an indirect?  In addition to the heat load he would like to provide his DHW with either a Superstor 30 or 45 gallon. 

SWEI

Indirect will work great

The ~37k output of the Cadet is more than a commodity 35-40k tank heater can produce, but not a lot more.  Price difference between a 30 and a 45 gallon should be minimal, so if they need the extra capacity I'd pick the larger one.

sgall

thanks for the quick response

and your input.  much appreciated.  SG