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heating options for winterized back "porch"

We have a 1916 rowhouse in D.C. with a two-story sleeping porch that we're planning to have insulated and converted into fully functioning rooms. On the bottom floor, we'll be knocking out of part of the back wall to expand the kitchen in this space.

I'm wondering what kind of heating system to have installed. The contractors who have looked at the project have all suggested electric baseboard heat because it would be quickest and cheapest.

I think I would prefer to extend the radiators, but I'm worried this could be difficult. One contractor said that it could be challenging to insultate the floor under the former porch well enough to prevent freezing in the winter. Another contractor said that radiators frequently don't work well when the system is expanded into this kind of space.

I really don't have a lot of money to spend on this project, so I'm sort of inclined to go with the baseboards. But we will be spending a lot of "living time" in the newly expanded kitchen, and I'd like to make sure we're doing this right.

Any pearls of wisdom?

Re: heating options for winterized back "porch"

Heating with electric would cost you a fortune.

You will have to do some calculations before you can determine if you have enough extra heating capacity in your boiler to extend out to the porches.

Examine the boiler to see if it has the BTU/HOUR HEATING CAPACITY listed on its front; if not, get the model # & make & contact the mfgr for this info.

You are looking for the boiler I=B=R OUTPUT RATING or the DOE OUTPUT RATING, and it should say something like "70,000 btu/hour net output".

You can use the sites below to calculate the HEAT LOSS CALCULATIONS for the original house AND the new additons to see if you have enough extra heat capacity on the boiler to heat the additions, as well as the original house.

If you have an oil-fired or gas-fired hot water boiler, you can usually easily upgrade to a slightly higher capacity using the same boiler (by using a larger nozzle, for example, on an oil-fired boiler).

New additions are usually put on a separate ZONE VALVE or ZONE CIRCULATOR, and the additions are given their own wall thermostat so the temp of the additions can be more precisely controlled.

Plastic PEX tubing is widely used these days to route a zone from the boiler room to the additions due to the high cost of copper, and the ease with which PEX can be snaked thru the walls & wall cavities to the new baseboard.

Consult the Yellow Pages under "Heating Contractors" to find someone who is experienced in installing and modifying hydronic (hot water) heating equipment; check the display ads for this.

Also consult the YP under "Heating Supplies-Equipment & Parts" and call the parts house counterman to get several referrals to experienced hydronic installers.

Install as much insulation as you possibly can into the new additons, in the exterior walls & in the floor.

A very rough way of calculating heating needs of a room or building, (assuming 8' ceilings) is to multiply the square footage of the room in question, or the house, and multiply by 40.

Thus a house 45' X 44.5' =2000 sq.ft. (rounded) X 40 = 80,000 btu/hr needed to heat this house.

(There are many factors that go into this HLC calculation, such as your location, the amount of glass you have, amt of insulation, etc.).

A room 15 X 15 = 225 sq.ft. X 40 = 9000 btu/hr to heat.

Baseboard puts out ~600 btu/hr; so 80,000 btu/hr divided by 600 = 134' of baseboard to heat the house.

Or for the room: 9000/600 = 15' of baseboard to heat the room.

The HLC's below are much more precise, especially the Slant Fin site, but it takes a long time to load.

Also Google "heat loss calculation" for additonal sites.

Please post back with basic info as to the type of boiler (gas/oil); its btu/hr capacity, sq. footage of house & additions.


Re: heating options for winterized back "porch"

Re: your back porch , winterized . Consider spray foam or
rigid insulation under the floor . these products do a lot
better job than batt insulation for this particular
situation . The density of the product offers air sealing
as well as higher r-value . No matter which way you go
with the heating , if the insulation does not
work properly & effectivley then you will not enjoy your
new rooms .


Re: heating options for winterized back "porch"

If your boiler is big enough you may want to consider radiant floor heat and the foam insulation.

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