Old House Renovation, New Heating System

ScoutRider · January 2021

Hello! My wife and I are renovating an old (pre-1850) house in southern Vermont. Th building has been gutted, so we expect to insulate as close to current standards as possible. The house is 2 floors, 2600 square feet, 2.5 baths. There are just the 2 of us, although there will be occasional visitors. Using a calculator I estimated the heating load at 143,000 BTU's. The old system was oil fired hot water with mixed cast iron and finned copper baseboard. The boiler is located in a modern utility room attached to the house on the ground floor. If practical, I would like to salvage the cast iron baseboard, replace/add finned copper where needed and use radiant in the 2 full baths.

I would like to use a propane fired combi boiler, but this is new tech to me, and the internet doesn't provide much clarity on what manufacturer i can find the best value from. Any advice on whether a combi system sounds right in this application, what manufacturers are "best" and anything else relevant would be much appreciated!

KC_Jones · January 2021

What calculator did you use for the heat loss? That number would make sense if the building wasn't insulated and some windows were open.

Are you set on doing a combi boiler? My opinion is a mod/con boiler with indirect would be a better choice, combi's always have some kind of compromise in them. If sized for the heating load you don't get high hot water production, if sized for hot water production they are oversized for the heating load, typically. Opinions vary on this subject.

As far as selecting equipment, it's said on here all the time, it is mostly about the installation than the equipment. Many online reviews blame the equipment when it's really a poor installation causing the problems.

Jamie Hall · January 2021

I can see that heating load in southern Vermont. It can get a wee bit chilly...

I agree with @KC_Jones that a mod/con with an indirect is the better choice, although sometimes folks do get lucky and find that a combi will work.

That said, however... it's all about installation and service. If you are going to have it installed by a contractor, he or she is critical, and it is essential that he or she is familiar and comfortable with the equipment chosen and will be there to maintain it. The more complex and advanced the system is, the more important this becomes. Indeed the most advanced systems require detailed understanding of the controls -- and each brand is different. Not better or worse, just different.

If this is to be a do-it-yourself installation, however, I would definitely recommend a really good, sturdy, reliable boiler with a minimum of controls, for which parts are readily available in your area. Not that I don't think you couldn't install and learn how to operate and maintain a more complex system -- I have no idea or opinion on that -- but I would wonder if you want to, or if you simply want reliable, easily understood, reasonably efficient heat...

TAG · January 2021

Getting a proper heat load is the key (total and room by room) -- what are you doing with the windows? I did a 1810 and am doing a 1873 now -- how is the 1850 constructed ? Have you thought about spray foam ?

If gutted you may be able to use radiant throughout if you can get the building tight and the loads down -- with propane you have to think about cost of the fuel ... plus there are always comfort issue in an old house with the way they are constructed. Foam solves lots of problems IMO ....

My 1810 was partially gutted and I was able to add radiant throughout (all the ceilings came down). The areas where I did not take down the plaster walls there was a need for additional BTU's as there was little insulation. I used panels ... but CI baseboard was discussed ... did not want to harm the great trim. Placed a panel under each window.

Robert_25 · January 2021

I don't know anything about combi boilers except they hate hard water on the domestic side, and limit your options when it comes to sizing. I suggest an indirect water heater if you have room in the mechanical room.

As for the heating load, I am not sure what you used for your calculations - but the heat load on a fully renovated 2600 sq ft house should not be anywhere close to that figure. Take another crack at it using the Slant Fin heat loss calculator and a heating design temperature of 0F: https://www.slantfin.com/slantfin-heat-loss-calculator/

For comparison, I live a few hours North in a 110 year old house, and have a heating design temperature of -5F. The house used to be about 2300 sq ft, and had a mix of blown-in insulation and fiberglass...and lots of drafts. I think the biggest heat load I ever observed based on boiler run-time was 50k btus/hr, and that was when it was below zero and windy. We recently completed a 700 sq ft 2-story addition that is insulated with spray foam, and replaced some windows in the old house - so far it appears that the overall heat load is about the same as it was before the addition.

EBEBRATT-Ed · January 2021

I agree the heat load calc is too high even for Vermont which the design is -10 in some areas

ScoutRider · January 2021

Thank you all for the comments. I'll go back and try the Slant Fin calculator. More research to do on my part. I want to get this right!

Shahrdad · January 2021

My house in St. Louis (2 1/2 story, brick walls, over 5,000 sq feet) has stayed toasty even when it's been -10 degrees with a 196,000 BTU boiler.

Jamie Hall · January 2021

Amazing what a difference outside conditions makes, isn't it? But the last time it got that cold in St. Louis was in 1996...

Old House Renovation, New Heating System

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