Temperature equalisation throughout the house

Question

We have been living in our home for a year now, so have seen both summer and winter, and we are now looking to solve the heating and cooling problems we have.

Heating

The walls and roof of the house are well insulated, and upstairs only has Velux windows, so apart from a brief spell when the combi-boiler stopped working (blocked condensate pipe) upstairs never has a problem with heating.

The open plan downstairs however is laminate flooring on concrete with minimal insulation, so the floor is always cold, and it's always a struggle to get it to feel warm in winter. Even with the heating water turned up to 80°C (176°F), the downstairs radiators fully on, and the upstairs radiators cold, a huge temperature differential remains.

Cooling

So far we haven't had many problems with downstairs being too warm in summer, but upstairs can get uncomfortably hot, especially in our bedroom.

Neither of us sleep too well if too hot, so we are currently looking at options for air-conditioning. I am concerned about our environmental footprint however and would prefer a more sustainable solution if possible.

Some Notes

All radiators except the upstairs bathroom towel radiator (which acts as a bypass radiator) are thermostatically controlled. We will probably convert them to smart TRVs at some point, but this is unlikely to help with the problems described here.

Downstairs consists of a small toilet room (2m²/22ft²), plus a large open plan area consisting of living and dining areas, stair well and kitchen which is also open to the conservatory (39m²/416ft²). All external doors open into this area.

The central heating is relatively new, so the condensing gas combi-boiler is quite efficient. It has a heat output of 24.9kW (to heat 77m² / 826ft² of house) and a SEDBUK rating of 90%.

In the UK gas is much cheaper for heating than electricity, we currently pay 3p/kWh for gas (at 90% boiler efficiency) and 11p/kWh for electricity (that's 3 & 16 cents/kWh at current exchange rates) so we would prefer the bulk of the heating load to be carried by the gas central heating.

Down the line we would like under floor heating downstairs, but we can't justify that right now. We will also eventually get around to replacing the patio doors and the conservatory, which should help with insulation downstairs, but again those are longer term plans.

Question

How can we equalise the temperature between upstairs and downstairs?

I thought of just fitting an insulated duct and a fan which extracts air from upstairs and pipes it downstairs, but the only place I could fit such a duct would be in the stair well, and it feels like the air would just end up circulating straight back upstairs. Other than that we would need to take a duct outside, which feels like a lot of work for an indeterminate benefit.

We have sought out quotes for a standard split air conditioner unit to cool upstairs, but that won't help with heating downstairs and I'm not happy about the environmental impact.

I was hoping that there may be solutions which could pump heat from upstairs to downstairs, but I don't know if split air conditioner systems can be configured to take advantage of temperature differentials like this.

• Note, I'm not looking for product recommendations, or someone to do a complete analysis of our situation, the detail is more to illustrate an example of the more general problem. What I am looking for is what would be considered a sustainable solution to the more generic problem of equalising temperature throughout a house with differing levels of heating and insulation.

Answer 1

Enclosing the stairwell would be a big help with the heating if it can be done with your floorplan.

Answer 2

You seem to be having issues with convection taking warm air upstairs, especially if you have extractors or vents taking air from upstairs bathrooms to the outside world. I have similar issues resulting in upstairs being too warm at the same time as downstairs is cooler than ideal if the heating has been on for some time, again in a well-insulated house. Like you I've got to the point of considering building in a fan to take air from the landing to downstairs (which is a hall plus an open plan living area in my case), but I can't find a way to fit it nicely.

Thick carpets or rugs and closing downstairs curtains will help a little with the winter temperatures. Shutting the bedroom door in the evening with the TRV in there low or off can reduce the amount of warm air convected in there, especially if it has an en-suite. The conservatory will be costing you a lot of heat. If you can't close it off with doors, consider (thermal) curtains across the opening, or adding any sort of window insulation you can in there

In summer, shading south-facing windows and opening windows only when outside is cooler than inside goes quite a long way. UK weather of course isn't consistent enough to experiment thoroughly. Opening downstairs windows at night makes a huge difference to convection but also to security so I can't recommend it for you. I'm ~100  km west of the location in your profile so similar climate but wetter.

Answer 3

Issue 1: Cold floor downstairs:

Installing a few ceiling fans that kept the air near the floor moving would help a lot.

Place area rugs where people's feet park helps a lot too.

If the slab is insulated below, then removing the laminate floor, adding radiant heat tubing to the floor, and casting another inch of concrete may be the best, but more expensive solution.

Issue 2: Overheated upstairs.

My grandparents house had grates in the floor upstairs over the kitchen. This allowed warm kitchen air (wood stove) to circulate to the bedrooms. The downside was the decrease in noise isolation. Many secrets were discovered at these grates.

Siting these grates is a balancing act: If you can put them over the ceiling fans, the those fans can be used to augment the circulation.

You have the opposite problem it's too hot upstairs. With a return path through grates, putting a ceiling fan in the stairwell may be sufficient. Failing that, put a fan in each grate. Not sure if these fans would work better blowing up with air returning through the stairwell, or blowing down. You want some form of speed control on these fans otherwise they can be obnoxiously noisy.

If the grate is above a ceiling fan, the ceiling fan may provide sufficient air pressure to make air flow through the grate.

You can also tap into the power use by lights for an embedded fan -- think of a 14" box fan between the floor joists with a grill on the ceiling below, and the floor above. A smaller fan is noisier than a large fan, and uses more power per thousand cubic feet of air moved.