Downsize a furnace or Zoned system

J_Logan

I recently replaced the 50 year old furnace while also converting the basement to an apartment. My tenants are always complaining about it being too cold downstairs as I'm the one in control of the temperature from the upstairs T-Stat.

I have a Goodman Model #CAPF1824B6DB 70,000 Btu gas furnace.

There is a main truck line in the floor cavity that services upstairs and downstairs with return air running right next to it. The unit is in the basement and sits on an outside wall in it's own closet. The basement is 800 sqft. with a great room and a bedroom separated by a wall. Literally two rooms and bathroom.

Options I can think of to get control or more heat to the basement...
Downsize furnace and block off lower heat/cool vents and add some form of heating downstairs?
Dual Zone heating?
Add a gas fireplace downstairs to provide additional heat?

J. Logan

Jamie Hall

Are there any returns intakes in the basement? If not, simply adding them (they should be at or near floor level) may help a lot but if they aren't there, there isn't much you can do to push warm air in -- since the cold air can't get out.

J_Logan

I should probably ask this another way.

What's the best way to isolate the two areas so that I control the heat upstairs and the tenant can control the heat downstairs?
Doesn't have to be off the same system, but that's a starting point.

To answer your question. Yes, there is return air downstairs.

DeBow

Zoning ductwork with dampers requires a survey to determine the zones are balanced. If one zone is disproportionally too small the furnace will over heat and cycle on the fan/limit control. That smaller zone would require a by pass duct from the supply to the return. This needs to be completed by a person who understands static pressure, FPM and CFM.

unclejohn

Those oil filled electric heat radiators are pretty safe and sounds like 2 will do it.

pecmsg

Just install a mini split for the basement area alone

mattmia2

Or even a console or wall furnace or 2.

EdTheHeaterMan

Is there Air Conditioning (cooling) associates with the system?

This is a classic example of trying to heat 2 different spaces with one central system. If 70,000BTU is needed to keep the building warm on the coldest day of the year, then a smaller furnace with zones does not solve the problem. If both zones call at the same time, the smaller furnace will not satisfy the load.

Now adding zoning dampers to direct more flow to the basement may violate the design criteria of having a minimum of 30% or 35% airflow for the smallest zone.

A separate heating source with a separate thermostat is needed for the basement. (how is the hot water made?) Maybe a gas water heater could have a heat exchanger added to create a small hydronic loop in the basement. Or just add some electric baseboard (the oil-filled mentioned above by @unclejohn are a good choice if high-temperature elements are a concern)

Ed

J_Logan

There is AC.

Smaller furnace with two zones: I was thinking same furnace two zones. I have no idea how zoning works and am assuming an air flow calc would determine whether the current system could handle zoning.

Water heater is natural gas.

I considered baseboards but am tapped out on current electrical panel for additional breakers.

Looks to me like my options are the oil filled that @unclejohn mentioned or a mini-split @pecmsg suggested. With the minisplit, would I need to downsize the current furnace?

J.

unclejohn

No you would leave the furnace alone. The mini splits are $$$$$$$$$$$$$$$$$$ the heaters are $

pecmsg

J_Logan said:

There is AC. Smaller furnace with two zones: I was thinking same furnace two zones. I have no idea how zoning works and am assuming an air flow calc would determine whether the current system could handle zoning. Water heater is natural gas. I considered baseboards but am tapped out on current electrical panel for additional breakers. Looks to me like my options are the oil filled that @unclejohn mentioned or a mini-split @pecmsg suggested. With the minisplit, would I need to downsize the current furnace? J.

I said a mini for the basement!

basements require heat while the upstairs requires cooling. 

J_Logan

Yes @pecmsg, that's exactly how I took what you were saying, mini-split for basement only.

GW

If you need to stick a motorized dampers in every run out, you’re going to pay some big bucks for a Zoning job. Or, Can the basement ducts-zone be ran independently, and tag into the furnace by itself? That would make the zoning costs more civilized

EdTheHeaterMan

Here is a typical duct design from a textbook. There are several similar diagrams to help the HVAC apprentice learn how the stuff works.

You can see a single central return that brings air from the home into the bottom of the furnace/AC air handler. the Plenum on top of the furnace collects the heated or conditioned air and directs it to the main trunk duct. Rooms get the conditioned air from the Take-offs that connect the registers in the room thru rectangular, round or oval pipes. some rigid and sometimes flexible.

In this doctored picture, you can see that zoning the basement (orange circle) registers separately from the first and second floor (green and blue circle) registers would be difficult because you would need to provide a motor-operated shut off damper for all 10 duct take-offs

to heat the basement only the two dampers would need to be open while 8 would remain closed. Your actual system may have more openings.

Dampers costing over $150.00 per register, and a control panel to operate them plus thermostats and wiring and the labor to install them. This is not normally done in the trade. gets too expensive and to many things to fail over the years.

Your comment that there is no room in the electric panel for Electric Baseboard is valid for a mini-split and also oil filled rad.

all three options would require some room to be provided.

The oil-filled radiator is an electric baseboard that does not get as hot and a non-oil-filled radiator. Still needs electricity to power the thing. As does the Mini-Split. You need to have an electrician that is familiar with Mini-Splits give you an estimate.