Heating the Attic


Old 08-22-16, 11:30 AM
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Heating the Attic

Hi all. I'm rehabbing a 100 year old 2 1/2 story house in St Paul MN and the attic never had any services, however it is a very livable space with proper stair access and end windows. The main parts of the house are heated with cast iron radiators getting hot water via a circulating pump on the boiler, IMHO the best method. My plan is to supply water to the attic and add maybe 2 radiators with gate valve shutoffs. I'm thinking this way the heat given off can be adjusted when winter comes around because I'd expect the attic to have the potential to be the warmest place in the house. Along with heating, both windows will be replaced with modern double glazed double hung windows and the attic will be fully insulated per current code using a combination of batt, rigid and/or possibly blown-in insulation, depending on finances. So far the lingering question is radiators; how many and how big. The area is about 30'x8'x12' with knee walls. Thinking ahead, we may add a partition wall someday splitting the area into two approximately square areas so the plan thus far is for two radiators, but we don't know how big they should be. I welcome any advise regarding radiators or any other aspects of this plan. Thanks in advance.
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Old 08-22-16, 12:53 PM
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The best way is to perform a heat-loss calculation for attic as you propose to modify it with insulation, windows, etc. There are sticky links at the top of this forum for Taco and Slant/Fin heat-loss programs. When you go to buy radiators, the manufacturer data will tell you the heat rating, per ft, as a function of water temp, say 180 deg, or whatever yours runs at.

You will want to use cast-iron radiators, possibly baseboard types - but the newer fin-tube convectors aren't compatible with your existing cast-iron rads. You will want to put the two new radiators on a separate zone or loop with its own thermostat in the attic. This is going to entail some new piping up from your boiler to the attic.

Gate valve shutoffs are passe -- use ball valves.

This is going to be a big job for a do-it-yourselfer. Be realistic about your experience and skills, or else hire a contractor.

A simpler way is to install electric baseboards or a mini-split unit - the latter would also provide air conditioning of the attic. Either of those alternatives will require a new 240-V electrical circuit.
Old 08-22-16, 01:16 PM
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A simpler way is to install electric baseboards or a mini-split unit - the latter would also provide air conditioning of the attic.
Is there AC up there now? I would be more concerned about that in an attic than heat.
Old 08-24-16, 06:36 PM
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I don't think think is beyond my skills as I've done similar improvements to a previous house as well as gained experience in all relevant trades, apprentice style. That said I have no issues with knowing my limits and get help where needed (I still have all my fingers).There is no AC and the cost of installation was just too much and around here, a decent window unit has always done the job for the hottest days. There is already 3/4 supply up to the attic that was done during the gut and rebuild of the lower floors. The wife can't stand the splits but there will be a little more discussion before that option is put to bed. I'll have a look at the links you mentioned. Thanks for the responses.
Old 08-25-16, 05:42 AM
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Get your design done and get it approved by your local code officials along with all needed permits.

MN has two climate zones, cold and colder and achieving the minimum insulation levels will be a challenge. Link below is for 2009 energy codes but some locations have moved on to 2012 or 2015 codes which may require more than the r-49 shown.

Below are other helpful links.

Creating a Conditioned Attic | GreenBuildingAdvisor.com

How to Build an Insulated Cathedral Ceiling | GreenBuildingAdvisor.com

Two Ways to Insulate Attic Kneewalls

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